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插入式密度计7826说明书


Technical Manual
78265004 September 2006

Solartron? 7826

7826 Insertion Liquid Densitometer
This manual covers the Frequency Output and Transmitter versions of the 7826

www.mobrey.com

Contents

7826 Insertion Densitometer - Technical Manual

Copyright ? 2006 Mobrey Ltd. All Rights Reserved Mobrey Measurement pursues a policy of continuous development and product improvement. The specification in this document may therefore be changed without notice. To the best of our knowledge, the information contained in this document is accurate and Mobrey Measurement cannot be held responsible for any errors, omissions or other misinformation contained herein. No part of this document may be photocopied or reproduced without the prior written consent of Mobrey Measurement.

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VERY IMPORTANT
HANDLE THE 7826 WITH CARE

DO NOT DO NOT

drop the 7826. use liquids incompatible with materials of construction. operate the 7826 above its rated pressure. pressure test beyond the specified test pressure. all explosion proof requirements are applied transmitter and associated pipework are pressure tested to 1? times the maximum operating pressure after installation. store and transport the 7826 in its original packaging.

DO NOT DO NOT ENSURE ENSURE

ALWAYS

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7826 Insertion Densitometer - Technical Manual

Contents
SECTION 1 - INTRODUCTION
1.1 ABOUT THE 7826 INSERTION LIQUID DENSITOMETER ................ 1-1
1.1.1 1.1.2 1.1.3 1.1.4 1.1.5 1.1.6 What is it?.......................................................................................... 1-1 What is it used for?............................................................................ 1-1 Measurements and calculations ....................................................... 1-2 Outputs from the frequency output version....................................... 1-2 Outputs from the transmitter version................................................. 1-2 Typical 7826 transmitter application ................................................. 1-3

1.2

EARLIER VERSIONS OF 7826 ........................................................... 1-5

SECTION 2 - MECHANICAL INSTALLATION
2.1 2.2 INTRODUCTION .................................................................................. 2-1 BOUNDARY AND VISCOSITY EFFECTS........................................... 2-2
2.2.1 2.2.2 Boundary effects ............................................................................... 2-2 Viscosity effects................................................................................. 2-4

2.3

STANDARD INSTALLATIONS............................................................ 2-5
2.3.1 2.3.2 2.3.3 2.3.4 2.3.5 2.3.6 7826 orientation................................................................................. 2-6 Free stream installation – flanged fitting .......................................... 2-7 Free stream installation – weldolet .................................................. 2-8 T-piece installation ........................................................................... 2-9 T-piece weldolet installation ........................................................... 2-10 Flow-through chamber installation ................................................. 2-11

2.4

INSTALLATION IN THE PIPELINE OR SYSTEM ............................. 2-12
2.4.1 2.4.2 2.4.3 2.4.4 2.4.5 2.4.6 Fluid at the sensor .......................................................................... 2-12 Thermal effects ............................................................................... 2-12 Flow rate ......................................................................................... 2-13 Entrained gas ................................................................................. 2-13 Solids contamination ...................................................................... 2-13 Example installation ....................................................................... 2-13

2.5

COMMISIONING ................................................................................ 2-14

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SECTION 3 - ELECTRICAL INSTALLATION
3.1 ELECTRICAL INSTALLATION – FREQUENCY OUTPUT VERSION ...3-1
3.1.2 3.1.3 3.1.4 General connections ......................................................................... 3-1 Installation considerations................................................................. 3-2 Post-installation checks .................................................................... 3-8

3.2

ELECTRICAL INSTALLATION – TRANSMITTER VERSION................3-9
3.2.1 3.2.2 3.2.3 3.2.4 3.2.5 3.2.6 3.2.7 3.2.8 Introduction ....................................................................................... 3-9 Installation considerations............................................................... 3-10 Wiring the 7826 transmitter ............................................................. 3-12 Power supply................................................................................... 3-12 Modbus (RS-485)............................................................................ 3-13 4-20mA Outputs .............................................................................. 3-14 Wiring procedure............................................................................. 3-15 Further information on RS-485 ....................................................... 3-17

SECTION 4 - USING ADVIEW (TRANSMITTER ONLY)
4.1 4.2 4.3 WHAT IS ADVIEW? .............................................................................4-1 INSTALLING ADVIEW .........................................................................4-1 STARTING ADVIEW ............................................................................4-2
4.3.1 Setting up serial communications ..................................................... 4-2

4.4

USING ADVIEW ...................................................................................4-5
4.4.1 4.4.2 4.4.3 4.4.4 4.4.5 4.4.6 4.4.7 ADView facilities................................................................................ 4-5 Menu bar ........................................................................................... 4-6 Configuring a slave address ............................................................. 4-6 Board configuration ........................................................................... 4-6 Data logging ...................................................................................... 4-9 Register Dump/load ........................................................................ 4-10 Register Read/write......................................................................... 4-11

SECTION 5 - CALIBRATION CHECK
5.1 CALIBRATION .....................................................................................5-1
5.1.1 5.1.2 5.1.3 5.1.4 Factory calibration............................................................................. 5-1 Calibration of Transfer Standards ..................................................... 5-1 Instrument calibration........................................................................ 5-1 General density equation .................................................................. 5-2

5.2

SAMPLE CALIBRATION CERTIFICATE.............................................5-3

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5.3

USER CALIBRATION CHECKS.......................................................... 5-5
5.3.1 5.3.2 Ambient air calibration check ............................................................ 5-5 On-line calibration adjustment........................................................... 5-5

SECTION 6 - MAINTENANCE
6.1 6.2 GENERAL ............................................................................................ 6-1 GENERAL MAINTENANCE................................................................. 6-2
6.2.1 6.2.2 6.2.3 Physical checks................................................................................. 6-2 Electrical checks ............................................................................... 6-2 Calibration check............................................................................... 6-3

6.3 6.4

MECHANICAL SERVICING................................................................. 6-3 FAULT ANALYSIS AND REMEDIAL ACTION ................................... 6-4
6.4.1 Time Period Trap............................................................................... 6-4

APPENDIX A - SPECIFICATION
A.1 7826 SPECIFICATION (FREQUENCY OUTPUT VERSION) ............. A-1
A.1.1 Specification ......................................................................................A-1

A.2

7826 SPECIFICATION (TRANSMITTER VERSION).......................... A-3
A.2.1 A.2.2 A.2.3 General..............................................................................................A-3 Specification ......................................................................................A-3 Factory default configuration.............................................................A-5

APPENDIX B - CALCULATED PARAMETERS (TRANSMITTER ONLY)
B.1 B.2 INTRODUCTION ................................................................................. B-1 BASE DENSITY REFERRAL ............................................................. B-2
B.2.1 B.2.2 Matrix density referral........................................................................B-2 API density referral............................................................................B-3

B.3

CALCULATED PARAMETERS .......................................................... B-5
B.3.1 B.3.2 B.3.3 B.3.4 B.3.5 B.3.6 B.3.7 Specific Gravity .................................................................................B-5 Degrees Baumé ................................................................................B-5 Degrees Brix......................................................................................B-5 Quadratic Equation ...........................................................................B-5 % Mass..............................................................................................B-5 % Volume ..........................................................................................B-5 API degrees.......................................................................................B-6

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APPENDIX C - SAFETY CERTIFICATION APPENDIX D - MODBUS COMMUNICATIONS (TRANSMITTER ONLY)
D.1 D.2

C-1

INTRODUCTION ................................................................................. D-1 ACCESSING MODBUS REGISTERS ................................................. D-2
D.2.1 Establishing Modbus Communications .............................................D-2

D.3

MODBUS IMPLEMENTATION............................................................ D-3
D.3.1 Register size and content .................................................................D-3

D.4 D.5

MODBUS REGISTER ASSIGNMENTS .............................................. D-4 INDEX CODES .................................................................................... D-7
D.5.1 D.5.2 D.5.3 D.5.4 D.5.5 D.5.6 D.5.7 D.5.8 D.5.9 D.5.10 D.5.11 D.5.12 D.5.13 D.5.14 D.5.15 API product type................................................................................D-7 Pressure, temperature, density and other units................................D-7 Special function.................................................................................D-8 Special function quadratic equation name........................................D-8 Special function quadratic equation units .........................................D-9 Output averaging time.......................................................................D-9 Analog output selection.....................................................................D-9 Referral temperature .........................................................................D-9 Alarm coverage ...............................................................................D-10 Alarm hysteresis..............................................................................D-10 Software version .............................................................................D-10 Hardware type.................................................................................D-10 User selected alarm variable ..........................................................D-10 Unit type ..........................................................................................D-11 Status Register flags .......................................................................D-11

D.6 D.7

ESTABLISHING MODBUS COMMUNICATIONS............................. D-12 EXAMPLE OF DIRECT MODBUS ACCESS .................................... D-14
D.7.1 D.7.2 Example 1: Reading line density (16-bit register size) ...................D-14 Example 2: Reading line density (32-bit register size) ...................D-14

APPENDIX E - REFERENCE DATA
E.1 CONVERSION TABLES ..................................................................... E-1
E.1.1 E.1.2 E.1.3 E.1.4 E.1.5 E.1.6 E.1.7
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Length units.......................................................................................E-1 Mass units .........................................................................................E-1 Mass flow units..................................................................................E-1 Volume flow units ..............................................................................E-2 Volume/capacity units .......................................................................E-2 Temperature units .............................................................................E-2 Pressure units ...................................................................................E-2

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E.1.8 E.1.9 E.1.10

Density units......................................................................................E-3 Dynamic viscosity units .....................................................................E-3 Kinematic viscosity units ...................................................................E-3

E.2

PRODUCT DATA.................................................................................E-4
E.2.1 E.2.2 E.2.3 E.2.4 Density/temperature relationship of hydrocarbon products ..............E-4 Platinum resistance law (to DIN 43 760)...........................................E-5 Density of ambient air (in kg/m3) .......................................................E-6 Density of water (in kg/m3 to ITS-90 temperature scale) ..................E-6

APPENDIX F - ELECTRICAL INSTALLATION OF OLDER EQUIPMENT
F.1 F.2 F.3 INTRODUCTION .................................................................................. F-1 CONNECTIONS TO OLDER SOLARTRON? EQUIPMENT............... F-2 7826 12-TERMINAL CONNECTIONS TO CUSTOMERS EQUIPMENT ........................................................................................ F-4

APPENDIX G - 4-20MA DIRECT DENSITY OUTPUT VERSION
G.1 G.2 INTRODUCTION ................................................................................. G-1 DENSITY RANGE SETTING .............................................................. G-1
G.2.1 G.2.2 50kg/m3 offset switch ....................................................................... G-2 Out-of-range behaviour .................................................................... G-2

G.3

ELECTRICAL INSTALLATION .......................................................... G-3
G.3.1 G.3.2 Non-EMC installation ....................................................................... G-3 EMC installation ............................................................................... G-4

G.4

CALIBRATION.................................................................................... G-8
G.4.1 G.4.2 In-line calibration .............................................................................. G-8 Out-of-range calibration ................................................................... G-9

G.5

7826 4-20MA OUTPUT VERSION SPECIFICATION ....................... G-10
G.5.1 G.5.2 G.5.3 Performance specification.............................................................. G-10 Power supplies ............................................................................... G-10 Environment ................................................................................... G-10

APPENDIX H - RETURNS FORMS

H-1

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1
Introduction
1.1
1.1.1

ABOUT THE 7826 INSERTION LIQUID DENSITOMETER
What is it?
The 7826 Insertion Liquid Densitometer is based on the proven Solartron? tuning fork technology. It is an all-welded sensor that is designed for insertion into a pipeline, open tank, or closed tank. Fluid density is determined directly from the resonant frequency of the tuning fork immersed in the fluid. A temperature sensor (PRT) is also fitted within the transmitter to indicate the operating temperature. The 7826 is available in two versions: a frequency output version, and a transmitter version. The frequency output version outputs the density measurement as a square wave signal, and features a PRT to output the operating temperature measurement. It is typically used with a signal converter, such as the Mobrey? 795x Series, and offers a powerful tool in critical density applications. The transmitter version incorporates much of the 795x signal converter functionality, such that online density calculations are performed locally within the electronics housing of the 7826. It features two 4-20mA outputs and RS485 Modbus communications, providing simple accessibility to all calculated values.

1.1.2

What is it used for?
The 7826 is ideally suited to applications where continuous, real-time measurement of density is required. For example, it can be used in process control where density is the primary control parameter for the end product, or is an indicator of some other quality control parameter such as % solids, or % concentration. Some examples are: Blending. Mixing. Evaporator control. End point detection in batch reactions. Interface detection in continuous separators. Interface detection in multi-product pipelines. Typical industries include: Oil and petrochemical. Brewing. Food. Pharmaceutical. Minerals processing (clays, carbonates, silicates, etc.)

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7826 Insertion Densitometer Technical Manual

1.1.3

Measurements and calculations
The transmitter version contains integral processing electronics to provide full in-situ configuration, enabling it to perform a variety of calculations. The 7826 continuously measures the following fluid properties: Line density (measured in kg/m3, g/cc, lb/gal, or lb/ft3). Operating temperature (measured in °C or °F). From these properties, the following are calculated: API base density at 15°C, 1.013bar; or at 60°F, 14.5psi. Base density (by using the matrix referral method.) °API. Specific gravity (S.G.) Special function calculations such as °Brix, °Baume, °Twaddle, % solids, etc.

1.1.4

Outputs from frequency output version
Outputs from the frequency output version of the 7826 include: Line density in g/cc – as a frequency (periodic time) signal. Line (operating) temperature in °C – as a PT100 signal. These outputs can be taken directly in by a Mobrey? 795x signal converter (or flow computer), which can then calculate live density-related parameters*: Base/referred density (using API tables or a matrix referral). Specific gravity. °API. °Brix % Solids. % Mass. % Volume. % Concentration. * Features vary between versions and issues of 795x liquid software. For information on electrical connections between the 7826 and a Mobrey? 795x unit, see Section 3.

1.1.5

Outputs from the transmitter version
No signal converter is required, which simplifies wiring and enables the 7826 transmitter to be connected directly to plant monitoring and control systems and/or a local indicator. Two forms of output are available: 1. Two 4-20mA analog outputs, factory set but individually configurable span, bias, limits, and filter options. The standard factory settings for these outputs are Line density on Analog Output 1, and Line temperature on Analog Output 2. Alternatively, the analog outputs may be controlled by one of the following: Line density.

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Introduction

Line temperature. °API. S.G. Base density (API).
? Base density (Solartron matrix referral method).

Special calculation result. 2. An RS485 (Modbus) interface, giving access to other measurement results, system information and configuration parameters. The 7826 transmitter is factory set to perform either API or Matrix referrals. Re-configuration of the 7826’s default settings (see Appendix A) is achieved by linking a PC to the Modbus (RS485) connection and running Mobrey Measurement's ADView software. After the 7826 is configured, the PC can be removed.

1.1.6

Typical 7826 transmitter application
Net Mass flow rate calculation Figure 1.1 shows and outline of a typical wet process mineral application where the 7826 transmitter provides a 4-20mA signal of the %solids determination from the slurry stream. From this signal and the measured volumetric flow rate, net mass flow rate is determined. The output signal could also be used for %solids control, or for net mass flow rate ratio blend control. The optional RS485 (Modbus) connection to a PC running Mobrey’s ADView software can be used for configuration and access to other measured values.

Net Mass calc.

Volume Flow Rate Magnetic Flow Meter

% Solids

7826 Transmitter

RS485

Mobrey’s ADView (WindowsTM Tool)

Figure 1.1: Typical 7826 transmitter application

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7826 Insertion Densitometer Technical Manual

PART NUMBER IDENTIFICATION
Code 7826 Product 7826 Insertion Densitometer Code Material A 316 Stainless steel with standard finish C 316 Stainless Steel, electro-polished F 316 Stainless steel, PTFE laminated tines V 304 Stainless steel, standard finish T Titanium, standard finish ? U Hastelloy B2, standard finish ? E Hastelloy C22, standard finish ? D Hastelloy C22, electro-polished ? G Hastelloy C22, PTFE laminated tines ? H Monel 400, standard finish ? J Monel 400, electro-polished ? L Monel 400, PTFE laminated tines Code Amplifier System A Frequency output, ATEX EEX d IIC T4 < 200°C B Frequency output, CSA Class 1 Division 1 Group C and D, < 200°C C Advanced: 4-20mA outputs, ATEX EEX d IIC T4, < 200°C D Advanced: 4-20mA outputs, CSA Class 1 Division 1 Group C and D, < 200°C Code Amplifier Housing A Aluminium alloy, T4 (-40°C < Ta < +110°C) Code Process Connections A 2” ANSI 150 RF B 2” ANSI 300 RF C 2” ANSI 600 RF D 2” ANSI 900 RF G 50 mm DIN 2527 DN 50/PN 40 H 50 mm DIN 2527 RF DN 50/PN 100 R 50 mm DIN 2527 DN 50/PN 16 K 3” Ladish Triclamp (Hygienic) M 3” IDF (Hygienic) N 1.5” Cone Seat Compression Fitting Code Stem Length A 0 mm (no stem extension and with standard spigot) Code Default Configuration (Amplifier Outputs) A API Degrees (Americas) B Base density to API tables (metric configuration) C Line Density only D General Process including Matrix (user data required) T No software configuration needed. Code Calibration Type L Density at 20 C Code Calibration Boundary A Free Stream B 2” schedule 40 boundary D 2” schedule 80 boundary E 3” schedule 80 boundary G 3” Hygienic Code Factory Set B Factory set option Code Traceability None A Material Certs X A C A A A B L B B A
(Typical Code)

7826

Note: Code “Z” (if used) denotes a non-standard option.

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1.2

EARLIER VERIONS OF THE 7826
Table 1.1 Part Number Identification (Earlier 7826)
7826XXX Flange Type: A = ASA 2 inch 150lb B = ASA 2 inch 600lb C = ASA 2 inch 1500lb E = 2 inch Ladish Tri-clamp F = 2 inch IDF Hygienic Flange J = 50mm DIN 2527 RF DN50/PN40 K = 50mmDIN 2527 RF DN50/PN100 N = Compression fitting cone seat 40mm (for weldolet and flow-through chambers) Output: C = Frequency Output D = 4-20mA Output * E = Frequency Output F = 4-20mA Output Material: A= E= F= G= H=

} }

Cat. IIC BASEEFA rated to EEx d IIC T4 CSA Approval to Class 1, Div 1, Group C Spigot ST STL 316L Hastelloy C22 ST STL 316L Hastelloy C22 Monel 400 Flange ST STL 316L Hastelloy C22 ST STL 316L Hastelloy C22 Monel 400

Vibrating Element ST STL 316L Hastelloy C22 ST STL PTFE Coated Hastelloy PTFE Coated Monel 400

* For CE conformance, this version must be used with a 7826 2A Electronic Filter (see Appendix B)

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2
Mechanical Installation
2.1 INTRODUCTION
There are a variety of external factors which affect the ability of the 7826 to operate successfully. In order to ensure that your system works correctly, the effects of these factors must be taken into consideration when designing your installation. There are two main aspects to consider: 1. The accuracy and repeatability of the measurements; 2. The relevance of the measurements to the overall purpose of the system. Factors which may adversely affect accuracy and repeatability include: The presence of gas or bubbles within the fluid being measured. Non-uniformity of the fluid. The presence of solids as contaminants. Fouling of the transducer. Temperature gradients. Cavitations and swirls caused by valves or discontinuities in the pipework. Operating at temperatures below the wax point of crude oils. The measured fluid being unrepresentative of the main flow. In some applications, absolute accuracy is less important than repeatability. For example, in a system where the control parameters are initially adjusted for optimum performance, and thereafter only checked periodically. The term achievable accuracy can be used to describe a measure of the product quality that can be realistically obtained from a process system. It is a function of measurement accuracy, stability and system response. High accuracy alone is no guarantee of good product quality if the response time of the system is measured in tens of minutes, or if the measurement bears little relevance to the operation of the system. Similarly, systems which require constant calibration and maintenance cannot achieve good achievable accuracy. Factors which may adversely affect the relevance of the measurements could include: Measurement used for control purposes being made too far away from the point of control, so that the system cannot respond properly to changes. Measurements made on fluid which is unrepresentative of the main flow. This chapter has the following sections: Section 2.2 - The importance of boundary and viscosity effects. Section 2.3 - Mechanical details for mounting and installing 7826. Section 2.4 - Optimising measurement accuracy and repeatability. Section 2.5 - Commissioning the system.
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2.2

BOUNDARY AND VISCOSITY EFFECTS
Unlike Mobrey Measurement’s tube density sensors, the tines of the 7826 are not totally enclosed. The walls of the pipe or tank, in which the transducer is installed, will introduce boundaries to the fluid flow, and this will have an effect on the calibration of the sensor. To overcome this, Mobrey Measurement calibrates the 7826 under a variety of pre-defined conditions, which correspond to the installation and pipe schedule. A calibration boundary is selected when ordering the 7826, so that, by calibrating the sensor under the same boundary conditions as the installation, the need for additional on site calibration is eliminated.

2.2.1

Boundary effects Any insertion device or transducer can only measure the properties of the fluid within the region of fluid to which it is sensitive. For practical reasons it is helpful to consider the sensitive or effective region for the transducer as an three-dimensional ellipse centred on the tips of the tines with its long axis aligned with the direction in which the tines vibrate, as shown in Figure 2.1. The 7826 is insensitive to the properties of the fluid outside this region.
long axis

short axis

Figure 2.1 Effective region of transducer If part of this volume is taken up by the pipework or fittings there is said to be a boundary effect; i.e. the intrusion of the pipe walls will alter the calibration. Figure 2.2 illustrates the 7826 installed in a pocket on the side of a 4” (100mm) horizontal pipe line (viewed from above). The effective region is completely enclosed within the pipe line, and thus is completely fluid.

2”Schedule 40 Pocket or “T”

4” horizontal pipe

Top or Plan view

Figure 2.2 Installation in a pocket (with horizontal pipe)

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Mechanical Installation

This next view shows other pipe outlines superimposed:

4” (100mm) vertical pipe

6”(150mm) vertical pipe

2”Schedule 40 Pocket or “T”

Top or Plan view

Figure 2.3 Installation in a pocket (with vertical pipe)

The smaller circle represents a 4” vertical pipe, which intersects the effective region. The 6” (150mm) pipe is the smallest pipe diameter to completely enclose the effective region when the pipe is vertical. Thus smaller pipe diameters can lead to a variety of different geometries which would each require a separate calibration. An alternative condition is shown in Figure 2.4, where the side pocket is extended until it passes completely through the effective region producing a “core”.

2”Schedule 40 Pocket or “T”

Top or Plan view

Figure 2.4 Installation in extended pocket

From this, it would appear that almost every installation requires a separate in-situ calibration - a very undesirable situation. The problem is resolved by providing standard calibration geometries which can be used in all pipe work configurations, and thereby allow the factory calibration conditions to be reproduced in the process. These standard geometries are described in section 2.3.

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2.2.2

Viscosity effects The 7826 can be affected by the viscosity of the fluid surrounding it. This is manifested in two ways: 1. An error in the density measurement, that is due to the effect of viscosity on the vibration of the fork tines. 2. In T-piece installations, where the 7826 is retracted into a pocket but away from the main fluid flow, high viscosity impedes the flushing of fluid near the tines. This may mean that, if a step change in density occurs, the fluid being measured will not representative of the fluid in the main flow, and the density response time may be extended significantly. A summary of these effects and the action to be taken to minimise them is given in Table 2.1: Table 2.1 Viscosity range T-piece installations only: Less than 100cP: Greater than 100cP: None required. Density measurements may be unpredictable; use flowthrough chamber or free stream installation. (Where the main flow is greater than 1.5m/s and there is no waxing present, the T-piece installation can be used for viscosities not exceeding 250cP.) All other installations: Up to 500cP Above 500cP None required. Density measurements may be unpredictable. Remedy

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2.3

STANDARD INSTALLATIONS
To overcome the need for in-situ calibration for every installation, three 'standard' installations are proposed. If an installation conforms to one of these standards, the factory calibration of the 7826 is valid, and in-situ calibration is unnecessary. The three installations are summarised below. Table 2.2 Standard installation Free stream T-piece (2” or 3” diameter, pipe or weldolet) 7826 tines are contained in a side pocket off the main flow, recessed by 25.4mm (1 inch). 0.5 to 3 m/s (1.6 to 9.8 ft/s) at main pipe wall. Up to 100cP (250cP in some cases). -50 to 200°C (-58 to 392°F). 50mm (2") or larger. Flow-through chamber

Description

7826 tines project directly into the main fluid flow.

7826 tines are contained in a flow-through chamber in which fluid is circulated from the main flow. 10 to 30 l./min (2.6 to 8 US gal./min)

Flow rate

0.3 to 0.5 m/s (0.98 to 1.6 ft/s) at the 7826. Up to 500cP.

Viscosity limits

Up to 500cP.

Temperature

-50 to 200°C (-58 to 392°F). 100mm (4") horizontal 150mm (6") vertical, or larger. Simple installation in large bore pipes. Ideal for clean fluids and non-waxing oils.

-50 to 200°C (-58 to 392°F). Any.

Main flow pipe size

Advantages

Simple installation in large bore pipes. Ideal for clean fluids and non-waxing oils.

Adaptable installation to any diameter main pipe and for tank applications. Ideal for flow and temperature conditioning. Fast response.

Drawbacks

Not suitable: For low or unstable flow rates. For small bore pipes.

Not suitable: For dirty fluids or slurries. For low or unstable flow rates. Where step changes in viscosity can occur. For small bore pipes. Where temperature effects are significant.

Careful system design required to ensure representative measurement. Frequently requires the use of a pump.

Note: For tank installations, always consult Mobrey Measurement.
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2.3.1

7826 orientation For Free-stream and T-piece installations, it is essential that the 7826 is always orientated with the transducer horizontal and the slot between the tines vertical. This is irrespective of the pipe line orientation, and helps to prevent the trapping of bubbles or solids on the transducer.

For ALL pipe and flow directions
. .

Bubbles rise!

the slot the slot must be must be

Solids sink!

vertical vertical

the 7826 the 7826 must be must be

horizontal horizontal

Note: It is important that the gap between the tines is vertical, as shown.

Figure 2.5 Orientation of the 7826

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2.3.2

Free stream installation - flanged fitting CAUTION: All drawings and dimensions given here are derived from detailed dimensional CAD drawings. They are given here for planning purposes only. Before commencing fabrication, reference should always be made to the current issue of the appropriate drawings. Contact Mobrey Measurement for details.

Conditions: Flow: Viscosity limit: Temperature: 0.3 to 0.5m/s (at the transducer) Up to 500cP -50 C to 200 C

Note that the thermal mass of the flanges may affect the response time of the transducer to temperature changes. The view shown below is schematic to show the dimensions of the side pocket, which is fabricated by the end user.

Figure 2.6 Flanged fitting of 7826

The pocket can be fabricated with 2” schedule 40 or 80 tube without affecting the calibration. Counter bore the pocket to a minimum depth of 13mm and diameter 52.6 ±0.1mm to locate the 7826 centrally. Weld neck or slip-on flanges may be used, according to the flange rating selected. However, for higher rated flanges, only slip-on flanges may give the necessary clearances.

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2.3.3

Free stream installation - weldolet CAUTION: All drawings and dimensions given here are derived from detailed dimensional CAD drawings. They are given here for planning purposes only. Before commencing fabrication, reference should always be made to the current issue of the appropriate drawings. Contact Mobrey Measurement for details.

This is the preferred option where temperature variations are a critical factor. The reduced thermal mass of the weldolet's taper-lock fitting renders it more able to track rapid changes in temperature. Conditions: Flow: Viscosity limit: Temperature: 0.3 to 0.5m/s (at the transducer) Up to 500cP -50 C to 200 C

The weldolet has a 1.5" taper lock fitting, and is supplied to be welded on 4", 6", 8" or 10" pipelines. Use of the weldolet ensures that the tines of the 7826 are orientated correctly and are fully inserted into the fluid stream. Before fitting the weldolet, the pipeline must be bored through at 52.5mm diameter to accept the viscometer. The weldolet must be welded to the pipeline concentrically with the pre-bored hole. The view shown below is schematic to show the relevant dimensions.

Horizontal: 4” or larger Vertical: 6” or larger

Weld Free stream weldolet to suit pipe diameter (4, 6, 8 or 10” N.B.)
111mm

52.5mm min

254mm

Free stream: 1.5” Swagelok fitting
Figure 2.7 Weldolet 1.5” Swagelok fitting of 7826

The installation will conform generally to Schedule 40 pressure ratings. The weldolet fabrication is rated to 100 Bar at ambient temperature. Note: Correct installation and pressure testing of the fitting is the responsibility of the user.

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2.3.4

T-piece installation Conditions: Flow: Viscosity limit: Temperature: 0.5 to 3.0m/s (at the main pipe wall) Up to 100cP, or 250cP under some conditions (See section 2.2.2) -50 C to 200 C

The thermal mass of the flanges may affect the response time of the transducer to temperature changes. Flow velocity at the pipe wall and fluid viscosity must be within the limits shown to ensure that the fluid within the pocket is constantly refreshed. This installation will not respond as rapidly as the free-stream installation to step changes in viscosity. The view shown is schematic to show the dimensions of the side pocket, which is fabricated by the end user.

4” or larger; horizontal or vertical

D

175mm +/-2mm

197mm

52.3mm wall thickness at least 3.912mm

2” Schedule 40

“T” piece Flanged

counter bore depth at least 13mm; diameter 52.6mm +/-0.1mm

Figure 2.8 T-piece (pocket) flanged fitting of 7826

The pocket geometry must be consistent with 2” schedule 40 tube in both internal diameter and minimum wall thickness, i.e.: Internal diameter: Minimum wall thickness: 52.5mm 3.192mm

Alternatively, schedule 80 tube may be used, but this affects the calibration, and must therefore be specified when ordering the sensor. Counter bore the pocket to a minimum depth of 13mm and diameter 52.6 ±0.1mm to locate the 7826 centrally. Weld neck or slip-on flanges may be used, according to the flange rating selected. However, for higher rated flanges, only slip-on flanges may give the necessary clearances.
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For normal flow conditions (up to 3m/s at the pipewall), the tines should be retracted 25mm from the main pipe wall. For higher flow rates, increase this by 10mm for every 1m/s increase in main flow rate. For hygienic applications, normal 2” hygienic tube is too thin for this application; (it can vibrate in sympathy with the fork, causing measurement errors). Use 3” hygienic tube and fittings instead, or fabricate hygienic fittings with the same wall thickness and internal diameter as those shown in the diagram above. 2.3.5 T-piece weldolet installation This is the preferred option where temperature variations are a critical factor. The reduced thermal mass of the weldolet's taper-lock fitting renders it more able to track rapid changes in temperature. Conditions: Flow: Viscosity limit: Temperature: 0.5 to 3.0m/s at the main pipe wall. (Operation is possible with higher flow rates, if dimension X is increased (see diagram below). Up to 100cP, or 250cP under some conditions (See section 2.2.2) -50 C to 200 C

The weldolet has a 1.5" taper lock fitting, and is supplied to be welded on 4", 6", 8" or 10" pipelines. Use of the weldolet ensures that the tines of the 7826 are orientated correctly and are fully inserted into the fluid stream. The length of the weldolet is determined by the flow rate in the main pipeline (refer to the table in Figure 2.9), and is chosen to ensure that the tines of the 7826 are sufficiently retracted from the main pipe wall. Dimension X should be the smallest possible, consistent with the maximum expected flow rate. Before fitting the weldolet, the pipeline must be bored through at 52.5mm diameter to accept the viscometer. The weldolet must be welded to the pipeline concentrically with the pre-bored hole. The view shown below is schematic to show the relevant dimensions. Flow velocity at the pipe wall and fluid viscosity must be within the limits shown to ensure that the fluid within the pocket is constantly refreshed. This installation will not respond as rapidly as the free-stream installation to step changes in viscosity.
264mm Carbon Steel Stainless Steel Y

DimY = Dim X - DimD + 43
Max flowrate 3 m/s 4 m/s 5 m/s 6 m/s Dim X mm 25.4 35.4 45.4 55.4

D X

Figure 2.9 The installation must conform to Schedule 40 pressure ratings. Alternatively, schedule 80 tube may be used, but this will affect the calibration, and must be specified when ordered the sensor. The weldolet fabrication is rated to 100 Bar at ambient temperature. Note: Correct installation and pressure testing of the fitting is the responsibility of the user.

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2.3.6

Flow-through chamber installation This chamber is fabricated by Mobrey Measurement, and is available with either weld prepared ends or with flange or compression fittings for connection into the process pipe lines. It is available with 1” or 2” inlet and outlet pipes. Note: The length of the inlet and outlet pipes must not be altered; otherwise, the temperature response and stability of the fitting may be adversely affected. Conditions: Flow: Viscosity limit: Temperature: Pressure: Constant, between 10 and 30 litres/minute. Up to 500cP. -50 to +200 C. 70 bar at 204°C, subject to process connections.

The PT100 is a direct insertion type, without a thermowell, and uses a ?" Swagelok connection. The diagram below shows the dimensions of this type of standard installation.
Note: Datum lines must be preserved when fitting flanges to weld-prepared tubes.
Dims in mm.

Flow out

1” Flange 1” Compr. 1” Weld 2” Flange 2” Compr. 2” Weld

A 480±3 477±2 416±3 483±2 522±2 409±2

B 335±3 332±2 271±2 345±2 384±2 271±2

Swagelok fittings

B

?” Flow in

1?”

Drain: ?” A

238mm (1” tubes) or 246mm (2” tubes)

Figure 2.10 The 1" Flow-through chamber For optimum results, the fluid flowing through the chamber should be homogeneous (plug flow). This can be achieved by installing a static mixer immediately before the chamber. Contact Mobrey Measurement for advice about using flow-through chambers in hygienic applications.

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2.4

INSTALLATION IN THE PIPELINE OR SYSTEM
Density is a sensitive indicator of change in a fluid, a key reason why density measurement is increasingly being chosen as a process measurement. This means that measurements can be sensitive to extraneous effects and therefore great care must be taken to consider all the factors which may affect measurement when assessing the installation requirements. Like many other transducers, the optimum performance of the density transducer depends upon certain conditions of the fluid and configuration of the process pipe-work. By introducing appropriate flow conditioning, the optimum performance of the 7826 can be achieved at any chosen location in the process system. You must first select a location which serves the application objective; e.g. installed close to the point of control. Then consideration can be given to fluid conditioning at that point. Where the application requirements allow a degree of tolerance in the point chosen for installation, the installation may be able take advantage of natural flow conditioning. The choice of mechanical installation (free stream, “T” piece or flow-through chamber) will be dictated partly by application needs and partly by the fluid conditions, such as: Condition of fluid at the sensor. Thermal effects. Flow rate. Entrained gas. Solids contamination.

2.4.1

Fluid at the sensor The fluid in the effective zone of the 7826 must be of uniform composition and at uniform temperature. It must be representative of the fluid flow as a whole. This is achieved either by mixing of the fluid either using a static inline mixer or taking advantage of any natural pipe condition that tends to cause mixing, such as pump discharge, partially open valves etc. The density transducer should be installed downstream.

2.4.2

Thermal effects For high viscosity fluids, temperature gradients in the fluid and in the pipe work and fittings immediately upstream and downstream of the transducer should be minimised in order to reduce the effect of viscosity changes. Always insulate the transducer and surrounding pipework thoroughly. Insulation must be at least 1”(25mm) of Rockwool, preferably 2” (50mm) and enclosed in a sealed protective casing to prevent moisture ingress, air circulation, and crushing of the insulation. Special insulation jackets are available from Mobrey for the flow-through chambers, which, because of the low volumetric flow rates and hence low heat flow, are more vulnerable to temperature effects. Avoid direct heating or cooling of the transducer and associated pipework upstream and downstream that is likely to create temperature gradients. If it is necessary to provide protection against cooling due to loss of flow, electrical trace heating may be applied, provided it is thermostatically controlled and the thermostat is set to operate below the minimum operating temperature of the system.

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In cases where it is necessary to heat or cool the fluid - to bring it within the temperature range of the transducer, for example - heat exchangers can be installed in the fluid flow. Mobrey Measurement can provide more details on this, or provide a complete system, if required. 2.4.3 Flow rate Flow rates and velocities should be maintained relatively constant within the limits given. The fluid flow provides a steady heat flow into the transducer, and the flow rate influences the self-cleaning of the sensor and the dissipation of bubbles and solid contaminants. Where it is necessary to install the transducer in a by-pass (either using the free stream installation in a 4” diameter horizontal by-pass, or a flow-through chamber), flow may be maintained using pressure drop, pitot scoop, or by a sample pump. Where a pump is used, the pump should be upstream of the transducer. 2.4.4 Entrained gas Gas pockets can disrupt the measurement. A brief disruption in the signal caused by transient gas pockets can be negated in the internal signal conditioning software, but more frequent disruptions or serious gas entrainment must be avoided. This can be achieved by observing the following conditions: Keep pipe lines fully flooded at all times. Vent any gas prior to the density transducer. Avoid sudden pressure drops or temperature changes which may cause dissolved gases to break out of the fluid. Maintain a back pressure on the system sufficient to prevent gas breakout (e.g. back pressure equivalent to twice the head-loss plus twice vapour pressure). Maintain flow velocity at the sensor within the specified limits. 2.4.5 Solids contamination Avoid sudden changes of velocity that may cause sedimentation. Install the transducer far enough downstream from any pipework configuration which may cause centrifuging of solids (e.g. bends). Maintain flow velocity at the sensor within the specified limits. Use filtration if necessary. Specify the 7826 transducer with a non-stick PTFE protective layer. 2.4.6 Example installation The diagram below illustrates some of the principles outlined in this section. It shows a free-stream density transducer installation with an additional sample take off. The position of both is such that the static mixing (which could be caused by pump discharge or partially closed valve), has negated the adverse effects of bends and established laminar flow, and has ensured that the fluid is thoroughly mixed and thus of uniform composition and temperature. The ideal place for a free stream or “T” piece installation, or for the by-pass take off point, is where the flow has just begun to be laminar. Note that the insulation extends upstream and downstream far enough to prevent conduction losses in the pipe walls from degrading the temperature conditioning of the fluid at the sensor.

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Centre

Heat Loss

Temperature

Density Heat Loss Swirl

Mixing produces a fluid which has uniform composition, and temperature and hence uniform density

Wall

Static mixing (or natural turbulence)

Turbulent flow

Onset of laminar flow

Onset of heat loss effects

Critical Insulation

Fork Densitometers or sample take off for by-pass installed sensors

Lower temperature Higher density Higher temperature Lower density

Figure 2.11

2.5

COMMISSIONING
1. Once the pipework installation has been prepared, and before installing the 7826, fit a blanking flange or compression nut to the 7826 mounting, and pressurise and flush the system. 2. Isolate the system, depressurise and remove the blanking flange or compression nut. 3. Install the 7826. 4. Slowly pressurise the system and check for leaks, particularly if the normal operating temperature is high, or the sensor has been fitted cold; tighten as necessary. 5. Once the system has stabilised and is leak free, fit the insulation material, remembering also to insulate any flanges.

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Electrical Installation
Note: If the 7826 Insertion Densitometer is to be operated in a hazardous area, the electrical installation must strictly adhere to the relevant safety information given in ATEX safety instructions booklet 78265061/SI, which will have accompanied this manual. If you have the frequency output version of the 7826…follow Section 3.1. If you have the transmitter version of the 7826…follow Section 3.2.

3.1
3.1.1

ELECTRICAL INSTALLATION – FREQUENCY OUTPUT VERSION
General connections
WARNING: Electricity is dangerous and can kill. Disconnect the power (from signal processing equipment) before making any connections.

The frequency output version of the 7826 receives its nominal 24Vdc power supply from signal processing equipment, such as the Mobrey? 795x Series of signal converters (or flow computers). The density signal negative terminal is connected to the 0Vdc power return line, and a four-wire PRT temperature signal completes the general installation wiring. The electrical cable enters the amplifier housing through a cable gland assembly. The terminal layout is shown in Figure 3.1.

Figure 3.1 Main terminal board connections on the 7826 (Frequency Output) Note: An earlier frequency output version of 7826 electronics used 12 terminals, not 8, and connection details for this are given in Appendix E.

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The amplifier housing has two chambers. One chamber contains the terminals for the 7826 / signal processing instrument interconnections, which is nearest to the cable gland axis. The other chamber contains the amplifier unit, its PCB encapsulated in a circular plastic container with the complete module secured in place by one keyway and one centrally positioned clamping screw. Connections from the sensor to the amplifier housing are via: Flying Leads: Plug/Socket: The temperature signal from the PRT embodied in the tine base. Coaxial cables carry the piezo drive and the sensor currents. The drive and sensor plug/sockets are displaced at right angles on the amplifier PCB perimeter.

Note:

The two-wire connection from the PRT probe terminates in the main output terminal block, where it is transformed into its four-wire configuration.

3.1.2
3.1.2.1

Installation considerations
Power supply Unless using the 24Vdc supply connections from a signal converter or flow computer e.g. Mobrey 795x Series, the power supply to 7826 must have the following specification: Voltage: Nominally 24Vdc, but in the range 23 to 25Vdc. Current: 42mA.
?

3.1.2.2

EMC To meet the EC Directive for EMC (Electromagnetic Compatibility), it is recommended that the 7826 be connected using a suitable instrumentation cable containing an overall screen. This should be earthed at both ends of the cable. At the 7826 end, the screen can be earthed to the 7826 body (and therefore to the pipework) using a conductive cable gland.

3.1.2.3

Ground connections It is not necessary to earth the 7826 through a separate connection; this is usually achieved directly through the metalwork of the installation.

3.1.2.4

Cabling Although it is possible to connect separate cables to the 7826 for power and the signal outputs, it is recommended that all connections are made through one instrumentation grade cable. The cables should conform to BS2538. In the USA, use Belden 9402 (two-pair) or Beldon 85220 (single-pair). Other cables that are suitable are those that meet BS5308 Multi-pair Instrumentation Types 1 and 2, Belden Types 9500, 9873, 9874, 9773, 9774, etc. The typical maximum recommended cable length for the above cable types is 1000m (3200ft.), but care must be taken to ensure that the power supply at the transducer is at least 23Vdc. Thus, for 24Vdc power supply, the overall resistance for the power supply connections (both wires in series) must be less than 100 .

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In order to complete the wiring, you will need the following parts: ?” NPT to M20 gland adapter. ?” NPT blanking plug. M20 x 1 cable gland (not supplied). The gland adapter and blanking plug are supplied with the 7826 – these two parts are EExd rated. However, you will need to get a suitably rated cable gland: For non-hazardous area installations, use an IP68 or higher rated cable gland. For hazardous area installations, use an EExd-rated cable gland. In hazardous areas, all parts must be explosion-proof. Alternative parts may be required in order to meet local electrical installation regulations. 3.1.2.5 Surge protection Careful consideration should be given to the likelihood of power supply surges or lightning strikes. The power supply connections of the 7826 have a surge arrestor fitted that gives protection against power supply transients. If there is a possibility of lightning strikes, external surge protection devices - one for each pair of signals and the power supply - should be installed as close to the 7826 as possible. Another method of surge protection is to connect an MOV (Metal Oxide Varistor) (breakdown voltage >30V) with an NE-2 neon bulb in parallel across each wire and ground. These can be mounted in a junction box close to the 7826. 3.1.2.6 Installation in explosive areas The 7826 is an explosion-proof and flameproof device. Therefore, the connections shown in the wiring diagrams (Section 3.1.3) are applicable. However, it is essential to observe the rules of compliance with current standards concerning flameproof equipment: 1. Electronics housing caps should be tightened securely and locked in position by their locking screws. 2. The electrical cable or conduit should have an appropriate explosion-proof cable gland fitted. 3. If any electrical conduit entry port is not used, it should be blanked off using the appropriate explosion-proof blanking plug, with the plug entered to a depth of at least five threads. 4. The spigot must be locked in place. In addition, refer to the safety information given in safety instruction booklet 78265061/SI, which will have accompanied this manual.

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3.1.3

Connections to signal processing equipment
WARNING: Electricity is dangerous and can kill. Disconnect the power (from signal processing equipment) before making any connections.

The frequency output version of the 7826 can be operated in two general environments, either in SAFE AREAS or in HAZARDOUS AREAS. When the 7826 is installed in hazardous areas: Refer to safety instruction booklet 78265061/SI for compliance with the ATEX standard, and other safety matters. Safety barriers and galvanic isolators are not required. However, Mobrey? 795x Series of signal converters and flow computers are not intrinsically safe, and MUST only be operated in a safe area. 3.1.3.1 System Connections (Mobrey? Equipment) CAUTION: Incorrect connection can damage the instruments.

System connections in non-hazardous areas are illustrated in the following diagrams: Figures 3.2 Figures 3.3 Figures 3.4 Typical 7826-7950 Signal Converter/Flow Computer interconnections Typical 7826-7951 Signal Converter/Flow Computer interconnections Typical 7826-7955 Flow Computer interconnections

Notes:

1. The terminal layout is shown in Figure 3.1 on page 3-1. 2. The main 24V dc power supply must supply between 23 and 25V dc at 25 - 42mA. 3. The ‘SIGNAL (-)’ and ‘SUPPLY (-)’ terminals on the frequency output version of the 7826 are internally connected. 4. System connections for the older 12-terminal versions of the 7826 and older signal converters/flow computers are given in Appendix F.

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3.1.3.2

Connections to a Mobrey? 7950 Flow computer/Signal converter
Frequency Output 7826 +
Supply 1 2 3 4 5 6 PRT 7 8

7950 Flow Computer/Signal Converter
Ch.1 PL9/1 PL9/2 PL9/4 PL9/3 PL12/1 PL12/2 PL12/3 PL12/4 Ch.2 PL9/5 PL9/6 PL9/8 PL9/7 PL12/5 PL12/6 PL12/7 PL12/8 Density power + Density input + Density power Density input PRT power + PRT signal + PRT signal PRT power -

+
Signal

-

PL9/9 PL12/9

PL9/10 PL12/10

Ground Ground

Figure 3.2 Typical 7950 connection to 7826 (NON-HAZARDOUS AREA)

3.1.3.3

Connections to a Mobrey? 7951 Flow computer/Signal converter
Frequency Output 7826 +
Supply 1 2 3 4 5 6 PRT 7 8

7951 Signal Converter/Flow Computer
Ch.1 PL5/9 (SK6/22) PL5/1 (SK6/14) PL5/10 (SK6/24) PL5/2 (SK6/15) PL7/1 (SK7/14) PL7/2 (SK7/15) PL7/3 (SK7/16) PL7/4 (SK7/17) Ch.2 PL5/9 (SK6/22) PL5/3 (SK6/16) PL5/10 (SK6/24) PL5/4 (SK6/17) PL7/5 (SK7/18) PL7/6 (SK7/19) PL7/7 (SK7/20) PL7/8 (SK7/21) 24V pwr + (+24V dc) Den ip + (Den +) 24V pwr (0V dc) Den ip (Den -) PRT pwr + PRT sig + PRT sig PRT pwr -

+
Signal

-

PL9/9 (SK6/25)

PL9/10 (SK6/25)

Ground (0Vdc) Ground (0Vdc)

PL5/10 (SK6/25) PL12/10 (SK6/25)

Figure 3.3 Typical 7951 connection to 7826 (NON-HAZARDOUS AREA)
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3.1.3.4

Connections to Mobrey? 7955 Flow computer/Signal converter
Frequency Output 7826 +
Supply 1 2 3 4 5 6 PRT 7 8

7955 Flow Computer
Ch.1 SK3/35 SK1/31 SK3/19 SK1/32 SK3/49 SK3/50 SK3/33 SK3/17 Ch.2 SK3/35 SK1/48 SK3/19 SK1/49 SK3/16 SK3/32 SK3/15 SK3/48

+24V Density Density Sig + 0V Density Density Sig PRT Power + PRT Signal + PRT Signal PRT Power -

+
Signal

-

SK3/19

SK3/19

0V Density

Figure 3.4 Typical 7955 connection to 7826 (NON-HAZARDOUS AREA)

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3.1.3.5

System connections (customer’s own equipment) CAUTION: Incorrect connection can damage the instruments.

The power supply requirements from the customer’s own equipment are as follows: For Density Transducer: For Transducer PRT: 21.6V to 26.4V dc, 25mA minimum 5mA dc maximum

The frequency at which the transducer is operating can be detected using a timer counter connected between the density output line and the negative power line. The electrical connections to be made are shown in Figure 3.5.

Frequency Output 7826 +
Supply 1 2 3 4 5 6 PRT 7 8 Power + Signal + Power Signal PRT Supply + 6V pk to pk

+
Signal

-

} PRT Signal
PRT Supply -

Figure 3.5 Electrical connections for use with customer’s own equipment (NON-HAZARDOUS AREA)

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3.1.4

Post-installation checks (electrical)
After installation, the following procedure will indicate to a high degree of confidence that the transducer is operating correctly: 1. Measure the current consumption and the supply voltage at the transducer amplifier. This should be: 23V to 25V dc 25mA to 42mA 2. With the 7826 in air, clean and dry, measure the periodic time of the output signal and check that it is as specified on the transducer calibration certificate (air check), making allowances for different ambient conditions.

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3.2
Note:

ELECTRICAL INSTALLATION – TRANSMITTER VERSION
If the transmitter version of the 7826 is to be used in hazardous areas, the electrical installation must strictly adhere to the relevant safety information given in ATEX safety instructions booklet 78265061/SI, which will have accompanied this manual.

3.2.1

Introduction
The transmitter version of the 7826 has two types of output: Two 4-20mA analog outputs that give an output proportional to a user-specified range. The parameters that can be output on each analog output are as follows:

Analog Output 1 Line density. * Base or referred density. Line temperature. Special Function parameter.

Analog Output 2 Line density. Base or referred density. Line temperature. * Special Function parameter.

* Factory default selection. A RS485 (Modbus) interface, giving access to other measurement results, system information and configuration parameters. The Modbus interface is also used to configure the 7826, using a PC running ADView software (see Chapter 4). It is recommended that both outputs types are installed, requiring a total of eight wires (two for each output, and two for power). Although you may not immediately require the Modbus connection, it may be required for in-situ calibration adjustment and future system enhancements, and the cost of the additional wires is trivial compared to the expense of installing them retrospectively. A number of factors must be taken into account when planning the electrical installation. These include: Use in hazardous areas Power supply EMC Ground connections Cables Surge protection Modbus connections Analog connections (ATEX safety instructions booklet 78265061/SI) (Section 3.2.2.1 and Section 3.2.4) (Section 3.2.2.2) (Section 3.2.2.3) (Section 3.2.2.4) (Section 3.2.2.5) (Section 3.2.5 and Section 3.2.8) (Section 3.2.6)

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3.2.2

Installation considerations
WARNING: Electricity is dangerous and can kill. Disconnect the power (from signal processing equipment) before making any connections.

3.2.2.1

Power supply The power supply to 7826 transmitter must have the following specification: Voltage: Current: Nominally 24V dc, but in the range 20 to 28V dc. >50mA.

If several 7826 transmitters are to be used within a local area, one power supply can be used to power them all; where the 7826 transmitters are distributed over a wide area and cabling costs are high, it may be more cost effective to use several smaller, local power supplies. Upon leaving the factory, the two 4-20mA analog outputs are non-isolated as they are powered through internal links to the power supply input. However, if split-pads “LNK A” (Analog Output 1) and “LNK B” (Analog Output 2) by the terminal block are ‘broken’, they become isolated and require a separate 20-28V dc power supply. (See section 3.2.6 for more details). If an RS232-to-RS485 converter is to be used (for example to connect to a serial port on a PC), this may also require a power supply. The power supply to the 7826 can be used to power the converter, or it may be more convenient to use a separate power supply. Care should be taken where there is the possibility of significant common-mode voltages between different parts of the system. For example, this can occur if the 7826 transmitter is local powered from a power supply which is at a different potential to the RS485 ground connection (if used). 3.2.2.2 EMC To meet the EC Directive for EMC (Electromagnetic Compatibility) it is recommended that the 7826 transmitter be connected using a suitable instrumentation cable containing an overall screen. This should be earthed at both ends of the cable. At the 7826, the screen can be earthed to the transmitter body (and therefore to the pipework), using a conductive cable gland. 3.2.2.3 Ground connections It is not necessary to earth the 7826 transmitter through a separate connection; this is usually achieved directly through the metalwork of the installation. The electronics and communications connections (RS485/Modbus and Analog 4-20mA) of the 7826 are not connected to the body of the 7826. This means that the negative terminal of the power supply can be at a different potential to the earthed bodywork. In the majority of applications, it is not necessary to utilise the RS485 ground connection. In areas where there is a significant amount of electrical noise, higher communications integrity may be obtained by connecting the negative power terminal (pin 2) of the 7826 to the communications ground. If this is done, it is important to ensure that the possibility of a ground loop, caused by differences in earth potential, is eliminated.

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3.2.2.4

Cabling Although it is possible to connect separate cables to the 7826 transmitter for power, RS485, and the analog outputs, it is recommended that all connections are made through one instrumentation-grade cable. Connections for the analog and Modbus signals should be individually screened twisted-pairs, with an overall screen, foil, or braid for the cable. Where permissible, the screen should be connected to earth at both ends. (At the 7826, this is best done using a conductive cable gland.) Cables should conform to BS2538. In the USA, use Belden 9402 (two-pair) or Beldon 85220 (single-pair). Other cables that are suitable are those that meet BS5308 Multi-pair Instrumentation Types 1 and 2, Belden Types 9500, 9873, 9874, 9773, 9774 etc. Maximum recommended cable length is 1000m (3200ft.), but care must be taken to ensure that the power supply at the transmitter is at least 20V. Thus, for 24V power supply, the overall resistance for the power supply connections (both wires in series) must be less than 100 ohms. In addition to the cable, to complete the wiring you will need: ?” NPT to M20 gland adaptor. M20 x 1 cable gland. ?” NPT blanking plug (not supplied). The gland adapter and blanking plug are supplied with the 7826 – these two parts are EExd rated. However, you will need to get a suitably rated cable gland: For non-hazardous area installations, use an IP68 or higher rated cable gland. For hazardous area installations, use an EExd-rated cable gland. In hazardous areas, all parts must be explosion-proof. Alternative parts may be required in order to meet local electrical installation regulations.

3.2.2.5

Surge protection Careful consideration should be given to the likelihood of power supply surges or lightning strikes. The power supply connections within the 7826 transmitter have a surge arrestor fitted to offer protection against power supply transients and, to some extent, indirect lightning strikes. If there is a possibility of lightning strikes, external surge protection devices - one for each pair of signals and the power supply - should be installed as close to the 7826 as possible. Another method is to connect an MOV (Metal Oxide Varistor) (breakdown voltage >30V) with an NE-2 neon bulb in parallel across each wire and ground. These can be mounted in a junction box close to the 7826. Further protection may be offered by the use of an independently powered, fully isolated RS485 to RS232 converter, which is essential whenever the Modbus output is permanently connected to a PC (See section 3.2.8).

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3.2.3

Wiring the 7826 transmitter
CAUTION: Incorrect connection can damage the instruments. Figure 3.6 shows the terminal board of the 7826 transmitter. To reveal the terminal board, it is necessary to unscrew the housing cap; the procedure is described in Section 3.2.7.

Note:

If the 7826 transmitter is to be used in hazardous areas, the electrical installation must strictly adhere to the safety information given in ATEX safety instruction booklet 78265061/SI, which will have accompanied this manual. The connections to the 7826 transmitter are: Power. Modbus (RS-485) communications. Analog outputs (4-20mA). It is recommended that you install all connections (eight cores) at installation, to avoid the possibility 2 of expensive alterations to the cabling at a later date. Typically, four pairs of shielded 19/0.30mm 2 (#16 AWG) to 19/0.15mm (#22 AWG) wires are used.

Figure 3.6: View of the terminal board of 7826 transmitter

3.2.4

Power Supply
Terminals 1 and 2 are for connecting an external 24V dc power supply, as guided in Figure 3.7. Ensure that the loop resistance of the cable(s) is such that the voltage at the 7826 transmitter terminals is greater than 20 volts. (The maximum voltage at the 7826 transmitter terminals is 28V dc.)

Figure 3.7: Power supply connections

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3.2.5

Modbus (RS-485)
Terminals 3 and 4 are for RS485/Modbus connections to a PC, as shown in Figure 3.4. For cable distances above 100 metres, see the ‘permanent installation’ details in Section 3.8.2. Note: The PC and converter are always located in a non-hazardous (safe) area. The RS485/232 converter and PC are not normally installed permanently. However it is strongly recommended that the wiring to the 7826 transmitter is made at the time of installation. For detailed information on RS485, see Section 3.2.8.

Note:

If you encounter communication difficulties with RS485, swap over the ‘A’ and ‘B’ signal connections at one end of the network.

TERMINAL BLOCK VERSION:

OR
9-PIN DIN CONNECTOR VERSION:

Figure 3.8: Modbus connections over < 100 metres

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3.2.6

4-20mA OUTPUTS
Terminals 5, 6, 7 and 8 are for connecting the two 4-20mA analog outputs to external devices, such as a signal converter. Upon leaving the factory, the two 4-20mA analog outputs are non-isolated as they are powered through internal links to the Power Supply Input. USING MAIN POWER SUPPLY:

However, if split-pads “LNK A” (Analog Output 1) and “LNK B” (Analog Output 2) by the terminal block are ‘broken’, they become isolated and require direct connections to another external 20-28V dc power supply. A second or third external 20-28V dc supply can be used.

USING A THIRD POWER SUPPLY:

Figure 3.9: 4-20mA Outputs

Note:

The external devices must be located in a non-hazardous (safe) area unless they are explosion proof and suitably certified.
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Fault conditions within the 7826 transmitter are indicated by a 2mA output. If this is detected, the Modbus link can be used to interrogate the transmitter to establish the likely cause of the problem.

3.2.7

Wiring procedure
1. Open the Terminal Board side of the 7826’s electronics housing by undoing the 2.5mm AF grub screw and unscrewing the lid anticlockwise.

VIEW FROM TOP OF 7826:
UNDO THIS CAP

GRUB SCREW

2.

With the 7826 mounted horizontally to ensure that the slot in the tines is vertical, the ?” NPT holes will be in a vertical plane. The cable entry should be at the lowest point, to help minimise water ingress. Fit the M20 gland adaptor into the lowest ?” NPT hole. Then, fit the M20 x 1 cable gland to the adapter. Fit a ?” NPT blanking plug to the unused hole.

(1) ?” NPT Blanking Plug. (2) ?” NPT to M20 adaptor. (3) M20 cable gland.

3.

Insert the cable through the cable gland and adaptor so that the multi-core cable is gripped leaving 200mm of free, unscreened wire to connect to the terminal blocks.

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4.

Wire up the cable cores as shown:

6.

When you have screwed the wires into the correct terminals, carefully tuck the wires around the electronics, and tighten the cable gland

7.

Finally, screw the housing cap on fully and tighten the locking grub screw using the 2.5mm AF hex drive.

VIEW FROM UNDERNEATH THE ELECTRONICS HOUSIN

TIGHTEN CAP

TIGHTEN HEX GRUB SCREW

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3.2.8
3.2.8.1

Further information on RS485
RS485 The 7826’s Modbus communications uses the RS485 electrical standard. This uses the difference between the two signal cores to transmit and detect logic levels, and is therefore able to tolerate significantly higher levels of common mode noise than RS232, which uses the voltage between the signal core and a common earth. A brief summary of some typical characteristics of the two standards is given below. RS485 Signal detection Receiver threshold Transmitter output swing Differential 200mV 0 to +5V (no load) +2 to +3V (120 ohm load) A converter is required for communication between the two standards. Further details are given in the next section. Only two signal connections are required for RS485, usually called A and B, sometimes ‘+’ and ‘-‘. RS232 Single-ended +1.5V ± 8V

Note:

Unfortunately, different manufacturers have interpreted the standard in different ways. Some have a ‘logic 1’ represented by signal A being more positive than signal B, others have made the opposite interpretation. If you encounter communication difficulties with RS485, the first remedy is to swap over the ‘A’ and ‘B’ signal connections at one end of the network.

For areas which may experience high common mode signals, a third conductor can be used as a ground reference for the communications signals. If used, this should be connected to Terminal 2 (Power supply negative) on the 7826. 3.2.8.2 RS485 to RS232 Converters are available from a number of sources, and can range from simple in-line devices that simply plug into a PC’s RS232 port, to programmable devices with full isolation between the two networks. Note: The 7826 transmitter uses a half-duplex implementation of RS485, such that the A and B signals are used for data transmission in both directions. This requires that the RTS line is toggled to indicate the transmission direction. This can be done by the host computer, or automatically by an RS485/232 converter which has the facility to do so. If you are using Microsoft Windows NT, 2000 or XP on your PC, you should use a converter which automatically changes RTS (as detailed below) otherwise the link may not work correctly. For simple installations, where the following conditions are valid, a simple in-line converter will be satisfactory: The Modbus network is less than about 50m (150ft). The number of devices on the bus is low. No common mode problems. Mobrey recommends the K2-ADE (Terminal Block type or DIN connector type) converter, manufactured by KK Systems Ltd and obtainable from Mobrey (part number 550003520); that will work with Microsoft Windows 98, NT, 2000 and XP.

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Mobrey’s optional ADView software kit includes: ADView software. K2-ADE RS485/RS232 converter (Terminal Block Version). The K2-ADE converter derives its power from the PC’s RS232 port RTS or DTR line, which must be held permanently in the high state. This is normally adequate for short distances where there are only a few devices on the network. However, the ability of the port to supply sufficient power is not guaranteed, especially for laptop PCs, and it may be necessary to connect an external power supply. This may also be necessary if using Microsoft Windows NT, 2000 or XP. To check the voltage levels, measure the voltages on the RTS input (pin 7) and the DTR input (pin 4) while the converter is connected to the PC (or other RS232 device). This procedure needs a breakout box (not supplied). Whichever input is powering the converter must have at least +6V during communications. Where the power is found to be insufficient, a 9V dc supply can be connected between Pin 9 (+) and Pin 5 (GND) of the RS232 connector. Connections are shown in Figure 3.10. See also the manufacturer’s technical information for details.

Figure 3.10: Powering the converter with an external 9V dc supply For permanent installations, and where the network length is more than 100 metres or so, Mobrey can supply the following DIN-rail mounted device from KK Systems Ltd. KD485-ADE (Mobrey part number 550003500) The KD485-ADE is three-way isolated, providing isolation between the two ports and the power supply. It requires a +7 to +35V power supply and typically takes 1 to 2W; (power consumption is largely independent of supply voltage). It is capable of working with Windows 98, NT, 2000 and XP. For a PC running Microsoft Windows NT/2000/XP, the RTS connection can be omitted.

Figure 3.11: Modbus connections > 100 metres

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The default configuration of the KD485-ADE has Port 2 configured for 9600 baud. This is the correct baud rate for the 7826 transmitter. (See Section 3.2.8.4 for details).

KD485-ADE
RS232 to RS485 Interface Converter/Isolator

1 2 3

Tx

Port 1 GND

6 5

Rx

RxB RxA

4 3 2 1

Port 1 RS232

4 5 6 RTS In Port 1 GND Switch 7 8 + Power Input -

Port 2 RS485

TxB TxA

The switch on the KD485-ADE should be set with SW1 On (to enable half-duplex operation on Port 2), with the other three switches (SW2, SW3, SW4) set to Off. Note: In most systems, the ground (GND) connection on pin 6 of port 2 will be unnecessary. When two or more devices are connected on the same RS485 network, this is known as a multi-drop configuration (see next section). Each device must be configured with its unique slave address before being installed on the network. 3.2.8.3 RS485 Multi-drop When several devices are connected in parallel on an RS485 network, this is known as a multi-drop network. Although it is theoretically possible to have up to 256 devices, in practice this is limited to around 32 or less, depending largely on the driving power of the Master. Each device has a unique slave address. For the 7826, this address must be individually programmed using the ADView software, before being connected to the multi-drop network (see section 4.4.3 for details).
Port 2 RS485
1 2 3 4 5 6 7 8

KD485-ADE
Tx Rx RTS In Port 1 GND + Power Input Port 2 GND RxB RxA TxB TxA

6 5 4 3 2 1

GND B A
GND A B 2 3 4

7826
A B

GND

2 3 4

7826

Wiring is quite straightforward: simply connect ‘B’ terminal to ‘A’ terminal, A to B. On some devices, the RS485 signals may be marked + and -. The + signal generally corresponds to the A signal, and the - signal to B. If you encounter communication difficulties with RS485, the first remedy is to swap over the ‘A’ and ‘B’ connections at one end of the network.

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3.2.8.4

Transmission mode The 7826 transmitter’s RS485 interface uses the following parameter settings, which are not selectable: Baud rate: Bits: Parity: Stop bits: 9600 8 None 2.

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Using ADView (Transmitter Only)
4.1 WHAT IS ADVIEW?
ADView is a software package provided by Mobrey Measurement to enable you to:
? Configure transmitter versions of Solartron densitometers and viscometers.

View and save data from them. Check that they are functioning correctly. ADView is installed on a PC and interacts with the transmitter version of a densitometer/viscometer through one of the PC’s standard serial (RS-232) ports. ADView requires Microsoft’s Windows operating system: Microsoft Windows 3.1, 95, 98, NT, 2000 or XP. Note: To connect to an RS-485/Modbus device, such as the 7826 transmitter, you will need an adapter between the PC and the 7826 transmitter (see Chapter 3). ADView provides many useful facilities, such as: Setting up serial link to communicate with the 7826. Configuring the transmitter version of a densitometer/viscometer. Displaying data in real time, or as a graph. Logging data to a file. Verifying correct operation of the system, and diagnosing faults. Loading or storing Modbus register values. Read/write to individual Modbus registers.

4.2

INSTALLING ADVIEW
Adview software is available for the PC on a variety of media (e.g. CD-ROM) and is freely available to download from the Mobrey Measurement web site (see back page). Procedure: 1. Identify the media containing the installation files for ADView. 2. Insert the media into an appropriate drive on your PC. 3. If the installation program does not begin automatically, run the set-up ‘.exe’ file that is on the media. (Note: This does vary between different PC operating systems. In general, open the File Manager or Windows Explorer, browse the drive containing the media and double-click on the set-up ‘.exe’.) 4. When the installation program starts, you will be asked to supply your name and organisation name for registration purposes, and supply a directory path into which ADView’s files can be loaded (a default directory path will be suggested).

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5. Follow the installation instructions until installation is complete. It will normally only take a few minutes. You can abandon the installation if you need to do so.

4.3

STARTING ADVIEW
Start the Adview software by navigating through the Start Menu to the program entry of Adview 6. Left-click on it once and the window shown below will then appear.

Note: Developments in ADView may mean that the screen shots differ slightly from the ones you will see on your PC screen.

Each of the six icons gives you access to the various facilities of ADView. You can choose to connect a Modbus device to one of the PC’s serial ports, or you can use ADView’s built-in simulation of the 7826. To run the simulation, choose Options -> Simulate board response from the menu bar and choose the ‘7825’ or ‘7826’ option. Then, click on the OK buttons, as necessary, to return to the main Adview screen. When simulation is chosen, ADView ignores the serial port and supplies simulated data. However, you do still need to click on the Communications Setup button followed by the Connect button. Then, click on the OK buttons, as necessary, to return to the main Adview screen.

4.3.1

Setting up Serial Communications
To operate with a real Modbus device, you will need to connect it to a suitable power supply (see the technical manual for the device) and need a connection to a serial port on the PC. Full details for connecting to the Modbus (RS-485) link on the 7826 transmitter are in Chapter 3. ADView automatically configures the selected port with the correct settings for the device. For the 7826 transmitter, this is 9k6 baud, 8 data bits, no parity, 1 stop bit, and Xon/Xoff (software) flow control. Note for Windows NT users An interesting feature of Windows NT is that it does not allow the RTS line to be toggled directly; any attempt to do so will result in a crash or other problem. Unfortunately, some RS485/232 converters require RTS to be toggled. To overcome this difficulty, ADView reads the OS environment variable to determine whether the operating system is Windows NT. If it is, ADView does not toggle RTS, and you will need to use an RS232/485 adapter which automatically switches the data direction without using RTS.

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To set the OS variable, click on the Start button, then choose Settings - Control Panel. Click on the System icon, and select the Environment tab. A list of environment variables and their values is shown. If OS does not appear in the list, type ‘OS’ (no speech marks) in the Variable text box, and ‘Windows_NT’ (no speech marks or spaces) in the Value box. To check whether the link is working, you can use ADView’s auto-detect facility. Select the correct PC port, and then click on the Connect button in the Communications dialogue box. ADView will set the port communications parameters, and then attempt to establish contact with any Modbus devices connected to the serial link, within the address limits set in the dialogue box.

When it finds a device, the message box below appears:

If no active device is found, a warning message is given:

In this case, check that the device is powered up correctly, that the cables and adapter are pushed fully home, and that the communications settings on the device and selected serial port are the same.
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4.4
4.4.1

USING ADVIEW
ADView facilities
The main ADView window gives access to the various facilities available. A brief description of each is listed below. Using the facilities is largely intuitive so that you can quickly learn the system.

Communications Setup (see section 4.3.1.) Sets up and checks RS-232/RS-485 communications.

Board Configuration (See section 4.4.4.) Enables you to select the measured parameter and range for the analogue output, and to configure density referral by entering matrix values or K factors, as well as special calculations, line pressure and averaging time. Displays instantaneous values of a selectable output parameter and the analogue output. Data logging (See section 4.4.5.) Provides tabular data from transmitters of line and base density, temperature and special function. One parameter can be displayed as a graph. Data can also be logged to a file in either Excel (tab delimited) or Notepad (space delimited) formats. The frequency at which results are logged can be set, and logging can be started and stopped.

Diagnostics Enables you to view: - live sensor readings - the status of the meter - values of working coefficients You can also verify calculations.

Transducer details Shows a list of details such as type, serial number, calibration dates, software version, etc.

Register dump/load With this facility you can dump the contents of all (or selected) Modbus registers from the device, or alternatively transmit values to them. File format is selectable (Excel/tab delimited, or Notepad/Space delimited).

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4.4.2

Menu bar
File Tools Exit Health Check Register Read/Write Exit ADView program. Determines whether the system is functioning correctly. A facility for reading or writing to any of the Modbus registers (see section 4.4.7) Enables you to specify exactly what will be transmitted on the Serial link (see Appendix D). Only used by Mobrey Measurement service engineers. Allows you to select between these two options

Direct Comms.

Engineer Status Options Simulate board response/ Actual Board Enable / disable screensaver

Allows you to select between these two options. When enabled, the screensaver operates as configured by the Windows system settings. Provides a means of opening or selecting ADView’s facilities.

Window

Help

About ADView

Displays software version number.

4.4.3

Configuring a slave address
The 7826 factory configuration sets the slave address to 1. However, in many applications it will be necessary to allocate another address. In a multi-drop application, where several Modbus devices are connected on the same network, it is essential to configure unique slave addresses for each device. To do this, you will need to run ADView and use the Register Read/Write facility, detailed in section 4.4.7. Check the value in Register 30 (Modbus Slave Address). If it is not the required value, enter the desired value and click on the write button. The 7826 will now be configured with the new slave address.

4.4.4

Board configuration
The 7826 configuration controls the way in which the transmitter will process and present data, user settings, calibration constants and other factors. This data is stored in non-volatile memory known as registers; a full list of the registers used in the 7826 is given in Appendix D. To configure the 7826, it is necessary to write data into the configuration registers using the RS485/Modbus link. ADView provides a convenient and graphical way of doing this without you needing to know about register addresses and data formats. Certain parameters are not available for configuration by ADView, including the Density Offset value which may be required to fine tune the calibration of the 7826 transmitter (see Chapter 5). However, ADView does have tools for reading and writing to individual Modbus registers (using the Tools -> Register Read/Write facility), and for direct communication on the Modbus (using Tools -> Direct Comms). More details and examples are given in Appendix D, but for the significant majority of applications these tools will not be required.

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The factory-installed default configuration is listed in Appendix A (Specification).

WARNING: There is no facility within ADView or the 7826 to ‘reset’ the transmitter to a default configuration. Therefore, before attempting any alterations to the configuration, you are strongly advised to use the Register Dump/Load facility in ADView to store the existing configuration (see section 4.4.5). Then, if any mishap occurs, you will be able to restore the configuration from the saved file.

ADView’s Board Configuration window is shown below: Shows which unit is being configured.

Enter values of variable to give 4mA and 20mA analogue outputs Select variable to control 4-20mA output. The calculated parameters (special functions) available depend on whether Matrix or API referral is selected. Select referral type (see text below for more details). Click on ‘Configure...’ to select and configure Special Function (calculated parameter). See text below for more details.

Select units for variable controlling analogue output.

Select from 1s to 100s, or no averaging.

Enter line pressure value here.

To exit from any of the configuration windows without making any changes, press the Escape key on your computer. Density Referral (Configure… button) To configure the density referral calculation, you will need to enter the relevant information. For matrix referral, this is a set of four values of density for each of up to five different temperatures; Appendix B gives more details on this. For API referral, you can select the product type, which automatically adjusts the coefficients of the General Density Equation (see Section 5), or enter your own values. Special Function (Configure… button) The range of special functions (calculated parameters) that are available depends on the referral type selected.

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Special Function Specific Gravity API° % mass % volume ° Baumé ° Brix User defined quadratic None

API referral

Matrix referral

When you select the Special Function you require, the configuration window will alter to allow you to input the relevant parameters, if applicable. Note that you can only select one Special Function to be available at any one time. When you are satisfied with the configuration, you should save it to a file, using the Register Dump/Load facility, as a safeguard against subsequent loss or alteration.

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4.4.5

Data logging
ADView’s Data Logging function is a useful tool for checking setups and performing experimental data capture. The diagram below explains some of the features. Graphical representation of analogue output.

For selecting the parameter to be logged.

Select analogue output of another densitometer.

Tabular display of instantaneous output of transmitter.

Use this button to start logging. Use this button to stop logging

For multi-drop configurations (see section 3.4.4), the output of up to three transmitters can be displayed simultaneously.

This button - which is activated when logging has been stopped enables you to configure the frequency of logging, where the logged data will be filed, and the format of the data. Use this button to select the transmitter and parameter to be displayed on the graph

Use this button to close Data Logging window Use this button to configure and display graph

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4.4.6

Register DUMP/LOAD
This facility is essential for saving the configuration of your 7826. You should use it to save the current configuration before you start to alter it, in order to restore it if things go wrong for any reason. Also, if you send the transmitter away for servicing or re-calibration, you should save the current configuration. Details are given below.

Address of unit being accessed

Enter desired filename for Dump, or required filename for Load.

Choose data delimiter (Dump only)

Choose which sets of registers to save to file, or simply save all of them. You can also specify individual registers.

Restore a previously saved set of register data from file.

Store the selected register data to a file.

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4.4.7

Register Read/write
In a few cases, it may be useful to write directly to a single Modbus register. Two likely occasions for using this feature are to set the Slave Address of the unit and to configure a density offset. Appendix D has a complete list of the 7826’s registers.

Warning: Before making any changes to individual registers, you should save the current configuration to a file (section 4.4.5) to safeguard your configuration if anything goes wrong.

From ADView’s menu bar, select Tools -> Register Read/Write. Click here to see complete list of Modbus register numbers and descriptors. Choose the one you want to access. For non-numerical values, click here to see complete list of possible entries and select one to write into the register. Enter numerical values directly.

The current register number appears here.

This button causes the current value of the chosen register to be displayed.

This button causes the current value to be written to the selected register.

You can read and write to any number of registers. When you have done all you want to, click this button.

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5
Calibration Check
5.1
5.1.1

CALIBRATION
Factory calibration
The 7826 Insertion Densitometer is calibrated within a standard physical boundary (typically 52.5mm diameter) against Transfer Standard instruments traceable to National Standards, prior to leaving the factory. Three fluids ranging in density from 1 to 1000 kg/m3 are used to establish the general density equation constants. The temperature coefficients are derived from the air point and material properties. The calibration procedure relies on units being immersed in fluids whose density is defined by Transfer Standards. Great attention is paid to producing temperature equilibrium between the fluid, the unit under test and the Transfer Standard. In this way, accurate calibration coefficients covering the required density range can be produced. All instruments are over-checked on water to verify the calibration. This check is monitored by the Mobrey Measurement Quality Assurance Department.

5.1.2

Calibration of Transfer Standards
The Transfer Standard instruments used in the calibration are selected instruments which are calibrated by the British Calibration Service Calibration Laboratory and are certified. Transfer Standard calibration uses a number of density-certified liquids, one of which is water. The densities of these reference liquids are obtained using the Primary Measurement System whereby glass sinkers of defined volume are weighed in samples of the liquids. Calibration of the Transfer Standard instruments is performed under closely controlled laboratory conditions and a calibration certificate is issued. Calibrations are repeated, typically every six months, producing a well documented density standard.

5.1.3

Instrument calibration
Each 7826 is issued with its own calibration which is programmed in to the instrument electronics before it leaves the factory. The calibration data is shown on a calibration certificate supplied with the instrument, an example of which is shown overleaf. The calibration contains four important pieces of data: (a) The instrument serial number. (b) The output signal/density relationship; this is based on three calibration points across the sensor’s operating density range. (c) Temperature coefficient data; this defines the correction which should be applied to achieve the best accuracy if the instrument is operating at product temperatures other than 20°C. (d) One instrument air data point for check calibration purposes.

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5.1.4

General density equation
The General Density Equation, used to calibrate the 7826 and shown in the Calibration certificate is: = K0 + K1. + K2. Where:
2

= calculated density. = time period (in s) of the tuning fork. K0, K1 and K2 are density coefficients.

When the 7826 is calibrated in a known environment, K0, K1 and K2 are selected to optimise the density measurement across the calibrated density range. As you can also see in the sample calibration certificate (in section 5.2), temperature effects are also compensated for using a second equation: ’ = Where: t (1 + K18(t - 20)) + K19(t - 20)

’ = the new (temperature compensated) density value. = the measurement temperature. K18 and K19 are temperature correction coefficients.

For the transmitter version of the 7826, values for all the K coefficients, shown on the calibration certificate, are programmed into the 7826’s registers, and should not be altered. If the 7826 is used in an application dissimilar to the one for which it was originally calibrated, it may be necessary to re-calculate the K coefficients. Contact Mobrey Measurement for further details.

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5.2
Note:

SAMPLE CALIBRATION CERTIFICATE
Figure 5.1 and Figure 5.2 are examples only. They are NOT the calibration certificate for your 7826.

CALIBRATION CERTIFICATE
7826F LIQUID DENSITY TRANSDUCER Serial No : XXXXXX Cal. Date : 09MAY06 Pressure Test : 230 BARS

DENSITY CALIBRATION AT 20 DEG. C AND AT 1 BAR DENSITY [KG/M3] 0 1.2 300 500 700 800 900 1000 1100 1600 PERIODIC TIME [uS] 1073.992 (1073.613)air check 1190.859 1262.255 1329.508 1361.790 1393.266 1423.993 1454.022 1595.144 DENSITY = K0 = K1 = K2 = K0 = K1 = K2 = K0 + K1.T + K2.T**2

-1.17560E+03 \ -2.31824E-01 } 300 - 1100 Kg/m3 1.23558E-03 / -1.16536E+03 \ -2.51436E-01 } 0 1.24443E-03 /

- 3000 Kg/m3

TEMPERATURE COEFFICIENT DATA Dt=D(1+K18(t-68))+K19(t-68) K18 = K19 = -2.1110E-05 +1.4825E-04

-------------| FINAL TEST & | | INSPECTION | | | | | | | | | -------------Ref No:- XX7826/Vx.x/XX/X DATE : 10MAY06

Figure 5.1: Example Calibration Certificate (Metric Units)

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7826 Insertion Densitometer - Technical Manual

CALIBRATION CERTIFICATE
7826F LIQUID DENSITY TRANSDUCER Serial No : xxxxxx Cal. Date : 09MAY06 Pressure Test : 3.34 kpsig

DENSITY CALIBRATION AT 68 DEG. F AND 0 PSIG DENSITY [ g/cc] 0 air 0.30 0.50 0.70 0.80 0.90 1.00 1.10 1.60 PERIODIC TIME [us] 1073.992 (1073.613) check 1190.859 1262.255 1329.508 1361.790 1393.266 1423.993 1454.022 1595.144 DENSITY = K0 = K1 = K2 = K0 = K1 = K2 = K0 + K1.T + K2.T

-1.17560E+00 \ -2.31824E-04 } 0.3 - 1.1 g/cc +1.23558E-06 / -1.16536E+00 \ -2.51436E-04 } 0.0 +1.24443E-06 /

- 3.0 g/cc

TEMPERATURE COEFFICIENT DATA Dt=D(1+K18(t-68))+K19(t-68) K18 = K19 = -1.173E-05 8.236E-08

-------------| FINAL TEST & | | INSPECTION | | | | | | | | | -------------Ref No:- XX7826/Vx.x/XX/X DATE : 10MAY06

Figure 5.2: Example Calibration Certificate (US Units)

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Calibration check

5.3
5.3.1

USER CALIBRATION CHECKS
Ambient Air Calibration Check
An ‘air check’ is a simple and convenient method to see if any long term drift, or corrosion and deposition on the tines, has occurred.

5.3.1.1

Ambient ‘air check’ procedure: 1. Isolate and, if necessary, disconnect the transducer from the pipeline. 2. Clean and dry the wetted parts of the transducer and leave them open to the ambient air. 3. Apply power to the instrument and check that the time period of the instrument agrees with the figure shown on the calibration certificate to within ±250ns. If the 7826 is not at 20°C, compensate for this by adding an offset of +250ns for every °C above 20°C, or by subtracting an offset of +250ns/°C below 20°C. 4. Refit the transducer to the pipeline if serviceable or remove for further servicing.

5.3.2

On-line calibration adjustment
An on-line calibration adjustment may be required if: (a) The physical boundary surrounding the tines is different from the physical boundary used for the factory calibration. (b) The viscosity of the fluid is greater than 500cP. (c) If the velocity of sound of the fluid is significantly different from the fluid used for the factory calibration. In practice this affects the density measurement by less than ±1 kg/m3. (d) If the unit has suffered long term drift or corrosion of the tines. The 7826 is a very accurate and stable instrument, and will normally provide good measurements. If it is suspected of giving incorrect results, you should confirm this by carefully checking the integrity of the fluid temperature measurement, and compare this with the temperature measurement given by 7826. You should also verify the integrity of the density check measurement. It is only after you have eliminated all other possible causes of error that you should attempt to make adjustments to the calibration of 7826. Normally the calibration adjustment is made by configuring a simple density offset into the instrument. If a more detailed calibration adjustment is required, such as a 2 or 3 fluid calibration adjustment for offset and scale, then refer to Mobrey Measurement.

5.3.2.1

Calibration adjustment procedure (for stable liquids) – frequency output 7826 1. On the signal processing equipment, set the line density offset to 0, and the line density scaling factor to 1. 2. Ensure that the system has reached its stable operating temperature. 3. With the 7826 operating at typical process conditions, draw off a sample of the liquid into a suitable container, and note the 7826 density reading and the operating temperature. 4. Measure the density of the sample under defined laboratory conditions using a hydrometer or other suitable equipment. Refer this to the operating conditions at the transducer. 5. Calculate the density offset required to make the 7826 measurement the same as the measured density of the sample. 6. On the signal processing equipment, enter the calculated line density offset.

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5.3.2.2

Calibration adjustment procedure (unstable/high-vapour-pressure liquids) – frequency o/p 7826 A pressure pyknometer and its associated pipework can be coupled to the pipeline so that a sample of the product flows through it. 1. On the signal processing equipment, set the line density offset to 0, and the line density scaling factor to 1. 2. Ensure that the system has reached its stable operating temperature. 3. When equilibrium conditions of product flow are reached, note the 7826 density reading and temperature, and simultaneously isolate the pyknometer from the sample flow. 4. Remove the pyknometer for weighing to establish the product density. 5. Compare the pyknometer reading with the 7826 reading and calculate the density offset required. 6. On the signal processing equipment, enter the calculated line density offset.

5.3.2.3

Calibration adjustment procedure (for stable liquids) – 7826 transmitter 1. Using ADView (see chapter 4), reset the line density offset (register 173) to 0, and the line density scaling factor (register 174) to 1. 2. Ensure that the system has reached its stable operating temperature. 3. With the 7826 operating at typical process conditions, draw off a sample of the liquid into a suitable container, and note the 7826 density reading and the operating temperature. 4. Measure the density of the sample under defined laboratory conditions using a hydrometer or other suitable equipment. Refer this to the operating conditions at the transducer. 5. Calculate the density offset required to make the 7826 measurement the same as the measured density of the sample. 6. Using ADView’s Register Read/Write tool (see section 4.4.7), configure the 7826 with the calculated line density offset (Register 173).

5.3.2.4

Calibration adjustment (for unstable or high vapour pressure liquids) – 7826 transmitter A pressure pyknometer and its associated pipework can be coupled to the pipeline so that a sample of the product flows through it. 1. Using ADView (see chapter 4), reset the line density offset (register 173) to 0, and the line density scaling factor (register 174) to 1. 2. Ensure that the system has reached its stable operating temperature. 3. When equilibrium conditions of product flow are reached, note the 7826 density reading and temperature and simultaneously isolate the pyknometer from the sample flow. 4. Remove the pyknometer for weighing to establish the product density. 5. Compare the pyknometer reading with the 7826 reading and compute the density offset required. 6. Using ADView’s Register Read/Write tool (see section 4.4.7), configure the 7826 with the calculated line density offset (Register 173).

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Calibration check

For further details on these procedures, reference should be made to: Institute of Petroleum: Petroleum Measurement Manual Part VII Section 1 – Method IP 160 Petroleum Measurement Manual Part VII Section 2 – Continuous Density Measurement Manual of Petroleum Measurement Standards Chapter 14 - Natural Gas Fluids - Section 6: Installing and proving density meters used to measure hydrocarbon liquid with densities between 0.3 and 0.7gm/cc at 15.56°C (60°F) and saturation vapour pressure, Sept 1979.

Institute of Petroleum:

American Petroleum Institute:

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Maintenance

6
Maintenance
WARNING: If the transmitter being serviced is to be used in a hazardous area, the rules of compliance with current standards concerning flameproof equipment must be strictly adhered to.

6.1

GENERAL
The 7826 Insertion Densitometer has no moving parts, and maintenance is limited to simple visual checks for leaks and physical damage. The Data Logging facility of Mobrey’s ADView software tool can be used whenever necessary to verify that the transmitter version of the 7826 is functioning correctly. Check calibrations should be carried out at specified intervals in order to identify a malfunction or deterioration in 7826 performance. If a fault or a drop in performance is detected, further tests are required to identify the cause of the fault. Remedial action is limited to cleaning the wet-side i.e. the tines, making good any poor connections, and replacing the internal electronics. In the extreme cases, the complete 7826 may need to be replaced.

Note:

The electronics within the 7826 transmitter contain calibration information relevant to that particular 7826 only. The circuit boards operate as a pair, and therefore both boards must be changed together. Contact Mobrey Measurement for more details if you need to change the boards.

CAUTION: Care is essential in handling of the transducer during its removal from and fitment to the pipeline/tank and during transportation. Wherever possible, retain and use the original packaging.

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6.2

GENERAL MAINTENANCE
This procedure is recommended for periodic maintenance and can also be used when fault finding.

6.2.1

Physical checks
(a) Examine the 7826, its electronics housing, and cables for any signs of damage and corrosion. (b) Make sure that the spigot connection is tight. (c) Check the 7826 for sign of leakage. (d) Check that there is no ingress of water/fluid into the electronics housing. (e) Ensure that the threads on the covers are well greased (graphite grease) and that the ‘O’ rings are in good condition.

WARNING: The covers MUST be completely screwed down and, in the case of an explosionproof enclosure application, DO NOT FAIL to tighten the locking screws.

6.2.2
6.2.2.1

Electrical checks
Electrical check for frequency output version of 7826 1. Carry out power supply and current consumption test at the transducer terminals T1 and T2 (or T3 and T4 as on older models with 12 terminals - see Appendix F). These should give: 25mA to 42mA at 22.8Vdc to 25.2Vdc If the current consumption is too high, replace the transducer amplifier module. 2. For a 7826 with a frequency output, and with the power supply still connected, ensure that the periodic time signal is present at terminals T3 and T4 (or T12 and T4 as on older models). This should give a signal amplitude of: Approximately 12V peak-to-peak (in air) For older versions of a 7826 with 4-20mA analog output (Appendix G): connect an ammeter in the analog output line, and check that the current is less than 20mA. 3. For a 7826 with a frequency output: check the 100 PRT (Platinum Resistor Thermometer) element by disconnecting the wiring to terminals T5 to T8 (T7 to T10) inclusive and measuring the resistance between terminals T6 and T7 (T8 and T9 for older versions). The value of resistance is temperature dependent and can be found in the Appendix E of this manual. 4. Carry out an insulation test on the transducer electrics as follows: (a) Disconnect all external leads from the terminal board. (b) Now short-circuit all the terminals together. Carry out an insulation test between the terminals and the transducer body, using the 500V dc insulation tester. The resistance must be greater than 2 M (current limited to 5mA). (c) Remove all short-circuits and reconnect the leads if required.

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Maintenance

6.2.2.2

Electrical check for transmitter version of 7826 Check the power supply and current consumption at the transmitter terminals, pins 1 and 2. These should give: 35mA to 42mA at 22.8V to 25.2V If the current consumption is outside this range, contact Mobrey Measurement’s Customer Service Team. (Contact details are on the back page).

6.2.3

Calibration check
(a) Carry out a check calibration as detailed in Chapter 5. (b) Compare the results obtained with the previous calibration figures to identify any substantial deterioration in transducer performance or any malfunction. Notes: 1. A drop in transducer performance is likely due to a build up of deposition on the tines which can be removed by the application of a suitable solvent. See section 6.3 below. 2. Malfunctions generally could be the result of electrical/electronic faults in either the transducer or the readout equipment. Always check the readout equipment first before attention is directed to the transducer.

6.3

MECHANICAL SERVICING
This mainly comprises the cleaning of any deposition or corrosion from the tines. Deposition is removed by the use of a suitable solvent. For corrosion, solvent and the careful use of a fine abrasive will usually be sufficient. However where extensive corrosion has been treated, it is highly recommended that a full calibration is carried out to check the transmitter characteristics. CAUTION: Care is essential in handling of the transducer during its removal from and fitment to the pipeline/tank and during transportation.

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Maintenance

7826 Insertion Densitometer - Technical Manual

6.4

FAULT ANALYSIS / REMEDIAL ACTION (7826 TRANSMITTER)
A fault may be categorised as either an erratic reading or a reading that is outside limits. Electrical faults can also cause symptoms that appear to affect the readings and it is recommended that the electrical system be checked first, before removing the transmitter for servicing.

6.4.1

Fault analysis and remedial action table

Fault Readings fluctuate slightly, i.e., are noisy.

Possible cause Analog output averaging time not long enough.

Remedy Increase the averaging time using ADView’s Board Configuration facility (see section 4).

Erratic readings.

Gas bubbles around tines. Cavitations. Severe vibration. Severe electrical interference. Large amount of contaminants.

Remove primary cause; e.g.: - install air release units to release gas. - apply back pressure to discourage formation of bubbles. - remove cause of vibration. Alternatively, it may be necessary to adjust the Time Period Trap (see section 6.4.2).

Readings outside limits.

Deposition and/or corrosion on the tines.

Clean tines (see section 6.3)

Analog output = 0mA.

No power to analog output. Analog output circuit failure.

If voltage across pins 5 and 6 is not 15 to 28V, replace power supply. Use ADView’s facility to set the analog output to 4, 12 or 20mA (in Board Configuration) to check whether the output is functioning. If not, replace circuit boards.

Analog output is 2mA

Alarm condition caused by lack of power to 7826 transmitter. Alarm condition caused by other internal failure.

If voltage across pins 1 and 2 is not 20 to 28V, check and replace main power supply. Use ADView Diagnostics to check that phase locked loop is in lock.

Temperature readings incorrect

If other readings from the 7826 transmitter are correct (i.e. analog output and Modbus appear to be functioning correctly), the temperature sensor has probably failed.

Return the 7826 transmitter to Mobrey Measurement for servicing. (See Appendix H for Returns Forms)

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Maintenance

Fault 7826 transmitter does not communicate with ADView

Possible cause Power failure to 7826 transmitter. Power supply to RS485/232 converter failed. A and B Modbus connections reversed. RS485/232 converter failed, wired incorrectly, or connected the wrong way round. ADView incorrectly installed on PC. Incorrect Slave address chosen for 7826 transmitter. RS232 port on PC failed.

Remedy Check power supply to 7826 transmitter and RS485/232 converter; replace if necessary. Check wiring. Try another RS485/232 converter.

Re-install ADView.

Check slave address.

Connect to another free RS232 port on the PC, if available. Alternatively connect a known working RS232 device to the PC to check that the port is working.

6.4.2

Time Period trap
Disturbances in the fluid caused by bubbles, cavitations or contaminants can cause sudden changes in the measured output, which may, under some circumstances, give rise to instability (i.e. hunting) in a control system relying on the measurement. The 7826 can maintain the analog output during such perturbations by ignoring the aberrant measurement, and maintaining the output at the last good measured value. This facility is known as the Time Period Trap (TPT). Under all normal circumstances, the factory settings for the TPT should be used. However, in extreme cases it may be necessary to alter the settings to meet the demands of a particular system. This should only be done after monitoring the behaviour of the system for some time, to establish the normal running conditions. Great care must be taken not to reduce the sensitivity of the transmitter so that normal response to fluctuations in the fluid is impaired. The time period trap facility works as follows: After each measurement of the time period (of the 7826’s vibrating tines) the new value is compared with the previous value. If the difference between them is smaller than the allowable tolerance, the output is updated to correspond to the new measured value, and the TPT remains inoperative; i.e., operation is normal. If the difference exceeds the allowable tolerance, the output remains at the its previous level, and does not follow the apparent sudden change in value.

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Maintenance

7826 Insertion Densitometer - Technical Manual

This process is repeated until either: (a) The latest measured value falls back to the level of the original value, indicating that the transient has passed; or (b) The TPT count is reached. At this point it is assumed that the change in value is not due to a random disturbance, and the output adopts the value of the latest reading. Two Modbus Registers control the operation of the Time Period Trap facility. These can be changed, if necessary, using ADView’s Register Read/Write facility (see section 4). Modbus Register 138: contains the maximum allowable change in the time period between readings, specified in s. The preset value is 10. Modbus Register 137: contains the Time period count, which is the maximum number of measurements to be rejected before resuming normal operation; the preset value is 2. If the value is set to 0, TPT is disabled, and the output will always follow the time period measurement. If you want to program another value, it should be determined experimentally, and be equal to the length of the longest undesirable transients which are likely to arise. If the value is set too high, the 7826 will be slow to respond to genuine changes in the fluid properties.

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A
7826 Specification
A.1
A.1.1
A.1.1.1

7826 SPECIFICATION (FREQUENCY OUTPUT VERSION)
Specification
Sensor performance Density measurement: Measurement technology Operating range Calibrated range Accuracy Repeatability Temperature coefficient 3 Uncorrected at 1000kg/m Corrected Fluid viscosity range Pressure effect Response time Temperature measurement: Temperature Technology Integral PRT Temperature Range Integral PRT Temperature Accuracy PT100 platinum resistance thermometer in tuning fork -50°C to +200 C (-58°F to +392°F) BS1904 Class B , DIN 43760 Class B Tuning Fork driven/sensed by piezoelectric crystals 0 to 3g/cc (0 to 3000kg/m3) (0 to 187.4 lb/ft3)
3 3 0.6 to 1.25g/cc (600 to 1250kg/m ) (38.5 to 80.25lb/ft )

0.001g/cc ( 1.0kg/m3) ( 0.06lb/ft3) 0.0001g/cc ( 0.1kg/m3) ( 0.006lb/ft3) -1.5kg/m3/ C 3 0.1kg/m / C 0 to 500cP Negligible 1 second nominal

A.1.1.2

Environmental Operating temperature range Process Ambient Maximum operating pressure Enclosure Type Protection Maximum weight Maximum vibration Vibration effect

-50 C to +200 C (-58°F to +392°F) -40 C to +85 C (-40°F to +185°F) 207bar (3000psi) Sand cast low copper alloy Polyurethane paint finish IP66 6.7 kg 0.5g continuous Negligible (acceleration 0.5g up to 200Hz)

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Specification

7826 Insertion Densitometer - Technical Manual

A.1.1.3

Transducer power requirements Minimum Input Voltage Maximum Input Voltage Current Consumption 23V dc 25V dc 25 - 42mA

A.1.1.4

Output Signals Frequency output (density): 875Hz 10 at 0kg/m3

720Hz 10 at 1000kg/m3 6V dc peak-to-peak nominal

PT100 output (temperature):

Four wires 100ohm 5mA PRT

A.1.1.5

Approvals EMC Approvals EN61326 ATEX II 2G EEx d IIC T4 CSA Class 1, Division 1, Group C & D T4

A.1.1.6

Electrical protection Reverse polarity protection. Power supply surge protection. EMI RFI protection to EN 61326.

A.1.1.7

Mechanical Materials: Dimensions: See Section 1 and safety instruction booklet 78265061/SI. See Section 2.

A-2

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Specification

A.2
A.2.1

7826 SPECIFICATION (TRANSMITTER VERSION)
General
The 7826 Insertion Densitometer comprises a vibrating fork density sensor, with processing electronics within the housing which provide full on node configuration; all signal processing, calculations, and calibration adjustments are made without the need for external electronics. Two off 4-20mA analog outputs are available: Analog Output 1 is factory set to output Line density, but can be controlled by other selectable parameters e.g. Base density from matrix referral. The zero and span are configurable. Analog Output 2 is factory set to output Line temperature, but can be controlled by other selectable parameters e.g. Base density from API calculation. The zero and span are configurable. An RS485 serial communications link is also available, which utilises the Modbus protocol to provide a means of configuring the device, retrieving data measurements, and performing diagnostics. ADView, a PC software application running under Microsoft Windows 3.1, 95, 98 or NT, is available for data logging, configuration and diagnostics purposes.

A.2.2
A.2.2.1

Specification
Sensor performance Density measurement: Measurement technology Operating range Calibrated range Accuracy Repeatability Temperature coefficient: 3 Uncorrected at 1000 kg/m : Corrected: Fluid viscosity range Pressure effect Tuning Fork driven/sensed by piezoelectric crystals 0 to 3 g/cc (0 to 3000kg/m3) 0.6-1.25g/cc (600 to 1250kg/m3) 1 kg/m3 0.1 kg/m3 -1.2 kg/m3/ C (typical) 3 0.1 kg/m / C 0 to 500cP Negligible

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Specification

7826 Insertion Densitometer - Technical Manual

Temperature measurement: Temperature Technology Integral PRT Temperature Range Integral PRT Temperature Accuracy A.2.2.2 Environmental Operating temperature range Max. operating pressure Enclosure Type Protection Max. weight Max. vibration -50 to +200 C (-58° to 392°F) 207 bar (3000psi) Die cast low copper alloy Polyurethane paint finish IP66 6.7 kg 0.5g continuous PT100 platinum resistance thermometer in tuning fork -50° to +200 C BS1904 Class B , DIN 43760 Class B

A.2.2.3

Transmitter power supply Minimum Input Voltage Maximum Input Voltage Current Consumption 20V 28V 35 to 45mA

A.2.2.4

Analog outputs Number of channels Range Alarm Condition Nominal Power Supply Maximum Terminal voltage Minimum Terminal voltage Isolation to Main Power Supply Accuracy @20 C Repeatability (-40 C to +85 C) 2 3.9mA to 20.8mA 2mA 24V 28V 15V 75Vdc rated 0.1% reading 0.05% FS 0.05% FS

A.2.2.5

RS485 Interface Connections Communications protocol Isolation Baud rate Termination A and B signals (screw terminals) Modbus RTU None - RS485 in same circuit as main power supply 9600 (fixed) not required

A-4

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Specification

A.2.2.6

Approvals EMC EN50081-2:1994 EN50082-2:1995 Approvals ATEX II 2G EEx d IIC T4

A.2.3

Factory default configuration
The 7826 can be supplied in one of three standard configurations (see Section 1.2, 7826 Options). For Factory Configuration Option A, Analog Output 1 is set to output Line Density in the units of kg/m3. Analog Output 2 is set to output Line temperature in units of °C. For Factory Configuration Option B, Analog Output 1 is set to output API base density in units of g/cc. Analog Output 2 is set to output Line temperature in units of °C. For Option C, Matrix referral is used to calculate the base density output, and the matrix will have been configured to the customer’s specification. All other default settings are as for Option A. The default values for these three configurations are shown below. Options A and C Analog Output 1 Variable Units 4mA setting 20mA setting Analog Output 2 Variable Units 4mA setting 20mA setting Alarms Coverage Line density kg/m 500 1500 Line temperature °C 0 100 General system Analog output User range Hysteresis Alarm user range Variable Units Low setting High setting Density calculations Temperature units Temperature offset Pressure units Pressure set value Line density units Line density scale factor Line density offset 2% Line density kg/m3 0 1000 °C 0 bar 1.1013 kg/m3 1 0
3

Option B Base density (API) g/cc 0.5 1.5 Line temperature °C 0 100 General system Analog output User range 2% Line density g/cc 0 1 °F 0 psi 14.5 g/cc 1 0

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Specification

7826 Insertion Densitometer - Technical Manual

Matrix referral

Reference temperatures Reference densities Base temperature

All 20 * All 0 * 20 * General crude +0000E+00 +0000E+00 15 1.1013 None 0 (None) None 998 0 0 0 1s

All 68 All 0 68 General crude +0000E+00 +0000E+00 60 14.5 None 0 (None) None 0.998 0 0 0 1s

API referral

Product type User K0 User K1 Base temperature Base pressure

Special Functions

Type Name Units Density of water (d) Density of Product A Density of Product B Quadratic coefficients (A,B,C)

Output averaging time Modbus Slave address Byte order Register size Hardware type

1 Big Endian 16 bit Advanced fork

1 Big Endian 16 bit Advanced fork

* For Option C, the Matrix referral constants will have been configured to the customer’s specification.

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B
Calculated Parameters (Transmitter Only)
B.1 INTRODUCTION
The 7826 Insertion Densitometer is capable of calculating a number of parameters based on the measured line density and temperature. These calculated parameters are often referred to as ‘special functions’. Only one calculated parameter is available at any one time; it can be used to control the analogue (4-20mA) output, and can also be accessed as a digital value (Modbus Register 260). This section describes the algorithms used in these calculations. The availability of the calculated parameters is dependent on whether Matrix or API is chosen as the density referral method. Special Function Specific Gravity API° % mass % volume ° Baumé ° Brix User defined quadratic None API referral Matrix referral

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Calculated parameters

7826 Insertion Densitometer - Technical Manual

B.2

BASE DENSITY REFERRAL
Base density is the density of the fluid at a specified base (or referral) temperature which is different to the line (i.e., the actual) temperature of the fluid. Base density can be calculated by either a Matrix referral method or by the API Referral method.

B.2.1

Matrix density referral
The Matrix Density Referral method uses a process of interpolation and extrapolation between a matrix of known density and temperature reference points to determine the liquid density at a specified base temperature different to the line temperature. A typical referral matrix is shown below.

T5 T4 T3 T2 T1

D1

D2

D3

D4

Line Density (measured) Line Temperature (measured) Base (Referred) Density B (calculated)

Temperature

Density

The lines D1 to D4 plot the density of four product types for which the density is known at five different reference temperatures, T1 to T5. Using this information, and the measured line density and temperature, the 7826 calculates the base density at the base temperature. The information required for the referral is: Five reference temperatures The density for each of four product types at the five reference temperatures (20 reference points in all) The base temperature, which must be one of the five reference temperatures. All 20 reference points must be specified, otherwise the 7826 cannot calculate the base density. If you do not have all the relevant data, enter a sensible estimate for the missing reference points. The easiest way of entering these values is by using the Board Configuration facility of ADView. Chapter 4 tells you how to do this.

B-2

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Calculated parameters

B.2.2

API Density referral
This calculation uses an iterative process to determine the density at the base temperature by applying temperature and pressure corrections using the API-ASTM-IP petroleum measurement tables. The information required for the API density is: Reference pressure and reference temperature Line pressure - this is not measured by 7826, and must be entered as part of the configuration. Product type: Refined product, crude product or user defined. Density/Temperature Relationship Correction factors in the revised API-ASTM-IP petroleum measurement tables are based on the following correlation equations: t/ where: t
15 15

= = = = =

exp ( -

15

t ( 1 + 0.8

15

t ) )

Density at line temperature t C. Density at base temperature 15 C. (t - 15) C. Tangent thermal expansion coefficient per deg C at base temperature of 15 C.

t
15

The tangent coefficient differs for each of the major groups of hydrocarbons. It is obtained from the following relationship:

K0
15

K1
2 15

15

where K0 and K1 are known as the API factors. Hydrocarbon Group Selection The hydrocarbon group can be selected as: General refined products General crude products User defined. K0 and K1 are programmed into the 7826 for the first two groups. For refined products the values of K0 and K1 are automatically selected according to the corrected density: Hydrocarbon Group Gasolines Jet Fuels Fuel Oils Density Range (kg/m?) 654 to 779 779 to 839 839 to 1075 K0 K1

346.42278 594.54180 186.9696

0.43884 0.0000 0.48618

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Calculated parameters

7826 Insertion Densitometer - Technical Manual

For Crude Oil the API factors are: Product Crude oil K0 613.972226 K1 0.0000

User defined factors can be entered as any sensible value.

Density / Pressure Relationship Isothermal secant compressibility can be defined by the simplified equation:

1 V0
where V1 P1 hence
0 1

V1 P1

t

where liquid volume changes from V0 to V1 as the gauge pressure changes from zero (atmospheric) to P1 = = = Isothermal secant compressibility at temperature t. Change of volume from V0 to V1 Gauge pressure reading (P - 1.013) bars.

1

P1
Corrected density at zero (atmospheric) gauge. Uncorrected density. (P - 1.013) where P is pressure in bars (P - base)

where
0 1

= = =

P1

A correlation equation has been established for from the available compressibility data; i.e., loge C = -1.62080 + 0.00021592t + 0.87096 x 106( 15)-2 + 4.2092t x 103( 15)-2 per bar. where = t = = C x 104 Bar Temperature in deg C
15

/ 1000 = oil density at 15 C (kg/litre)

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Calculated parameters

B.3
B.3.1

CALCULATED PARAMETERS
These are also known as Special Functions.

Specific gravity
Base density (@ Tref) Density of water (@Tref)

Specific Gravity (SG)

B.3.2

Degrees Baumé
(Only available when Matrix referral is selected.)
Degrees Baumé = 145 145 Base density

where Base density is measured in g/cc.

B.3.3

Degrees Brix
(Only available when Matrix referral is selected.) Degrees Brix = 318.906 384.341 SG 66.1086 SG2

where SG is Specific gravity.

B.3.4

Quadratic Equation
(Only available when Matrix referral is selected.) The following quadratic equation is implemented:
2 B B

y

A

B

d

C

d

where:A, B ,C are User programmable constants. d
B

= density of water (also a programmable constant). = base density.

B.3.5

% Mass
(Only available when Matrix referral is selected.) % mass of product A = where:K1 = base density of product A K2 = base density of product B
B

K1 B K 2 * 100 B K1 K 2

= base density.of mixture

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Calculated parameters

7826 Insertion Densitometer - Technical Manual

B.3.6

% Volume
(Only available when Matrix referral is selected.) K2 % volume of product A = B * 100 K1 K 2 where: K1 = base density of product A K2 = base density of product B
B

= base density.of mixture

B.3.7

API Degrees
(Only available when API referral is selected.)
API 141.5 131.5 SG

(The base density used for specific gravity value is determined from API density referral.)

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C
Safety Certification
For details of ATEX safety certification, refer to the ATEX safety instruction booklet (78265061/SI), which will have accompanied this manual.
For details of all other safety certification, contact Mobrey Measurement.

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Safety Certification

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D
Modbus Communications (Transmitter Only)
D.1 INTRODUCTION
The Modbus/RS485 communications facility on the transmitter version of the 7826 can be useful in a number of ways. It is the only means of configuring the transmitter, and also gives access to diagnostic information not available on the analogue output. Digital representations of the measured and calculated parameters are also available which lead to higher accuracy, and greater integration in digital networks and systems. The RS485 serial interface of the 7826 communicates using the RTU Modbus protocol, which is a well established system used in many industrial applications. The protocol defines the way in which messages will be transmitted between Modbus devices, and details how the data will be formatted and ordered. It is beyond the scope of this manual to give a full description of the protocol, but a useful reference on Modbus is the "Modbus Protocol Reference Guide" (PI-MBUS-200 Rev..D). (1992) published by Modicon Industrial Automation Systems Inc., Massachusetts. A Modbus network can have only one Master at any one time, with up to 32 Slaves. The 7826 acts as a slave device, and only communicates on the network when it receives a request for information from a Master device such as a computer or a PLC. The implementation used on the 7826 is fully compliant with the Modicon Specification. All information is stored in memory locations in the 7826 referred to as Modbus Registers. These store all the data required to control the operation, calculations and data output of the 7826. Modbus communication with the transmitter consists of reading or writing to these registers. The 7826 implements only two Modbus commands: Command 3 Command 16 (1016) Read Modbus Register, and Write Modbus Register.

Any number of registers can be read with Command 3, but only one register can be written to for each Command 16. This restriction does not limit the performance of the system, since all functions are mapped into the register structure in one way or another. In most cases, it is unnecessary to understand the detail of the protocol, as this is taken care of by the application program. For example, Mobrey Measurement’s ADView software enables you to configure the transmitter, and even read or write to individual Modbus registers, without you needing to know about Modbus. However, if you are using a proprietary software package, or developing your own application software, the information given in this section will be invaluable.

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7826 Insertion Densitometer - Technical Manual

D.2

ACCESSING MODBUS REGISTERS
Any device which can drive the RS485 interface on the 7826 can, in theory, access the Modbus registers. In practice, some sort of user interface is required to simplify the process. ADView, which is distributed with the 7826, offers several ways of accessing the registers. Board Configuration: A graphical interface for viewing and setting the main configuration parameters of the 7826. Direct access to registers is not offered. Register Read/Write This tool provides a simple window from which to read and write to named and numbered registers. When you write to a register, you are presented with a set of allowable values from which to choose. Thus the tool is only useful for communicating with Mobrey Measurement transmitters. This is the simplest and most foolproof way of directly accessing the registers. Section 4 gives full details. This is another tool which allows you to compose a sequence of data to be transmitted to/from the Modbus. This can be used to communicate with any Modbus device, providing that you know the register addresses, data format, indices, etc. The composition of the data is entirely up to the user, although the tool does compute and insert a checksum. Only those well versed in the use of Modbus protocol should attempt to use this facility. It is mainly designed for testing Modbus transmissions which are subsequently to be used in an application specific environment. A worked example of using this tool is given in section D.7.

Direct Communications

D.2.1

Establishing modbus communications
If the transducer Slave address or the values of Registers 47 and 48 are not known, Modbus communications cannot be carried out successfully, and it will be necessary to establish the current values in these items. If you are using ADView, you can search for the addresses of all connected slaves, and then interrogate the appropriate registers for each one. If you are not using ADView, section D.D.6 gives a procedure which will enable you to ascertain this information.

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Modbus Communications (Transmitter Only)

D.3
D.3.1

MODBUS IMPLEMENTATION
Register Size and Content
All registers are 32 bits (whether they are integer or floating point types), although the Modbus specification states that registers are 16 bits and addresses and ‘number of register’ fields assume all registers are 16 bits long. All floating point values are in IEEE single precision format. Registers are contiguous in the Modbus register ‘address space’. There is a one-to-one mapping of 32-bit 7826 register numbers to 16-bit Modbus register numbers. Therefore, only the full 32 bits of any register can be accessed. The upper and lower 16-bit segments have the same Modbus register number and consequently cannot be individually read. Registers 47 and 48 within the 7826 allow the Modbus ‘dialect’ to be changed to suit the communicating device if it cannot easily be re-programmed. This is most easily done using ADView’s Register Read/Write tool (see Chapter 4). Their usage is as follows: Modbus Byte Ordering Register 47 contents 0000000016 FFFFFFFF16 Modbus Register Size Register 48 contents 0000000016 FFFFFFFF16 Modbus Register size 16 bits 32 bits Modbus Byte Ordering Big Endian (i.e. MSB first) Little Endian (i.e. LSB first)

16 bit Register Size (Register 48 = 0000000016) In order to read 32-bit registers when Modbus registers are dealt with in units of 16 bits, you must specify twice the number of 32-bit register you want to read in the ‘number of registers’ field. E.g., to read one 32-bit register, use '2'. If an attempt is made to read an odd number of registers, the command will fail. 32 bit Register Size (Register 48 = FFFFFFFF16) In order to read 32-bit registers when Modbus registers are dealt with in units of 32 bits, you specify the actual number of registers you want in the ‘number of registers’ field. (E.g. To read two 32-bit registers in this mode, use '2'.)

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Modbus Communications (Transmitter Only)

7826 Insertion Densitometer - Technical Manual

D.4

MODBUS REGISTER ASSIGNMENTS
Each register is identified by a unique number, and the list is organised by this number. For each register, the contents are described, along with the data type of the contents. The data type is always 32 bits unless stated otherwise. Variable names are given for reference purposes only. They have no other use. Note: All units’ locations (registers 3, 4, 5 and 26) MUST be set before entering other values. In some cases the data in a register is used to represent a non-numerical quantity, known as an index. For example, the units of density can be kg/m3, gm/cc, lb/gal or lb/ft3 and these are represented by the numbers 91 to 94. Thus if Register 3 (line density) contains the value (index) 91, this means that the units of line density are kg/m3. Index values may, of course, be used for more than one register. Tables of these indices are given in section 0.

Register 0 1 2 3 4 5 6 7 8 9 10 11 14 15 16 17 20 21 22 23 24 25 26 27 29

Function API product type API referral reference temperature API referral reference pressure Line density units Base density units Temperature units Special function calculation type Special function quadratic equation name Special function quadratic eqn. Units Output averaging time Analog Output 1 selected variable Analog Output 2 selected variable PWM factor for 4mA on Analog Output 1 PWM factor for 20mA on Analog Output 1 PWM factor for 4mA on Analog Output 2 PWM factor for 20mA on Analog Output 2 PRT calibration factor Crystal oscillator calibration factor Diagnostics flags Line density value when fixed by diagnostics Base density value when fixed by diagnostics Temperature value when fixed by diagnostics Pressure Units Referral temperature for matrix referral Alarm coverage
1

Data Type Long integer 4-byte float 4-byte float Long integer Long integer Long integer Long integer Long integer Long integer Long integer Long integer Long integer Long integer Long integer Long integer Long integer 4-byte float 4-byte float Long integer 4-byte float 4-byte float 4-byte float

Index Table (where applicable) D.5.1

D.5.2 D.5.2 D.5.2 D.5.3 D.5.4 D.5.5 D.5.6 D.5.7 D.5.7

D.5.2 Long integer Long integer D.5.8 D.5.9

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Modbus Communications (Transmitter Only)

30 31 47 48 49 61 64 65 66 67 68 69 127 128 129 130 131 132 137 138 139 140 141 146 147 - 151 152 - 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185

Modbus Slave address Hysteresis on alarm output on analog output Modbus byte order Modbus register size Software type Hardware type Write-protected copy of PRT factor Write-protected copy of crystal factor
Write-protected copy of Analog Output 1 4mA PWM factor Write-protected copy of Analog Output 1 20mA PWM factor Write-protected copy of Analog Output 2 4mA PWM factor Write-protected copy of Analog Output 2 20mA PWM factor

Long integer Long integer D.5.10 D.3.1 D.3.1 Long integer Long integer 4-byte float 4-byte float Long integer Long integer Long integer Long integer Long integer 4-byte float 4-byte float 4-byte float 4-byte float 4-byte float Long integer 4-byte float 4-byte float 4-byte float 4-byte float 4-byte float 4-byte float 4-byte float 4-byte float 4-byte float 4-byte float 4-byte float 4-byte float 4-byte float 4-byte float 4-byte float 4-byte float 4-byte float 4-byte float 4-byte float Long integer 4-byte float D.5.13 D.5.11 D.5.12

Stored checksum for the FRAM K0 K1 K2 K18 K19 Transducer time period trap count Transducer time period trap (difference in s) Time period value when fixed by diagnostics Value represented by 4mA on analog output Value represented by 20mA on analog output Line pressure Temperatures for matrix referral Densities for matrix referral Atmospheric pressure Line density offset Line density scaling factor Special function calculation parameter A Special function calculation parameter B Special function calculation parameter C Special function parameter d / density of water Density of product A for special function calc. Density of product B for special function calc. Temperature offset User K0 value for API referral User K1 value for API referral User selected alarm variable User range (alarm) high value

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Modbus Communications (Transmitter Only)

7826 Insertion Densitometer - Technical Manual

186 192 193 194 195 196 201 202 203 204 256 257 258 259 260 261 262 263 264 265 266 267/8
*

User range (alarm) low value Write-protected copy of K0 Write-protected copy of K1 Write-protected copy of K2 Write-protected copy of K18 Write-protected copy of K19 Unit’s original calibration date Unit’s most recent calibration date Unit’s serial number Unit type Status Register Corrected line density
* *

4-byte float 4-byte float 4-byte float 4-byte float 4-byte float 4-byte float Long integer Long integer Long integer Long integer Long integer 4-byte float 4-byte float 4-byte float
*

D.5.14 D.5.15

Corrected base density Line temperature
*

Special function calculation result Transducer time period (in s) * FRAM calculated checksums PRT resistance (in ohms)
*

4-byte float 4-byte float Long integer 4-byte float

Transducer coil pickup level (in volts) Transducer resonance Q value
2

*

4-byte float 4-byte float

Electronics board temperature (in °C) Software version string * String

These are live values. Although they can be written to, it would be pointless. Special function units are not used in units conversions (they are for indication only), so can be set at any time. 2 This value is only valid when bit 3 (hex 08) is set in the diagnostics flag register (22), after a 1 second pause.
1

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Modbus Communications (Transmitter Only)

D.5

INDEX CODES
This section provides an interpretation of the numerical indices used to represent non-numerical values.

D.5.1

API product type
Used in Register 0. (The user values for K0 and K1 are stored in Registers 182 and 183.) Index 0 1 2 Product Type Crude (general crude) Refined (general product) User K0 and K1

D.5.2

Pressure, Temperature, Density and other Units
Used in Registers 3, 4, 5 and 26. Index 6 7 10 11 12 32 33 57 90 91 92 93 94 101 102 104 Units psi A bar A kg / cm? Pa kPa °C °F % SGU g / cm? kg / m? lb / gal lb / ft? ° Brix ° Baume heavy ° API

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Modbus Communications (Transmitter Only)

7826 Insertion Densitometer - Technical Manual

D.5.3

Special Function
Used in Register 6. Index 0 1 2 3 4 5 6 7 Calculation none % mass % volume Specific Gravity ° Baume ° Brix General Quadratic Equation ° API

D.5.4

Special Function Quadratic Equation Name
Used in Register 7. Index 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Name none Density % Mass % Volume ° Baume ° Brix Specific Gravity Gravity API Plato Twaddle ° Alcohol (reserved) (reserved) (reserved) (reserved) (reserved) (reserved) (reserved) (reserved)

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Modbus Communications (Transmitter Only)

D.5.5

Special Function Quadratic Equation Units
Used in Register 8. Index 0 57 Name none %

D.5.6

OUTPUT Averaging Time
Used in Register 9. Index 0 1 2 3 4 5 6 7 Averaging Time none 1s 2s 5s 10 s 20 s 50 s 100 s

D.5.7

Analogue Output Selection
Used in Register 10. Index 0 1 2 3 4 5 6 Output Density Referred Density Temperature Special Function 4 mA 12 mA 20 mA

D.5.8

Referral temperature
Used in Register 27 Index 0 1 2 3 4 Highest temperature value in matrix Referral Temperature Lowest temperature value in matrix

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Modbus Communications (Transmitter Only)

7826 Insertion Densitometer - Technical Manual

D.5.9

Alarm Coverage
Used in Register 29. Bit Pattern 0x00000001 0x00000008 0x00000010 Coverage 4 - 20 mA output 1 alarm System error User defined alarm

D.5.10

Alarm Hysteresis
Used in Register 31. Index 0 1 2 3 4 5 4 - 20 mA Output Hysteresis 0% 0.5 % 1% 2% 5% 10 %

D.5.11

Software version
Used in Register 49. Index 0 1 Density Referral Matrix API

D.5.12

Hardware type
Used in Registers 61. Index 1 Meter Type Advanced Fork

D.5.13

User selected Alarm Variable
User in Register 184. Index 0 1 2 3 4 5 6 7 Variable Line density Base density Temperature Time Period PRT resistance Special Function Pickup level None
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Modbus Communications (Transmitter Only)

D.5.14

Unit type
Used on Register 204. Index 5 Transmitter type Advanced fork

D.5.15

Status Register Flags
Used in Register 256.
Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Hex Value 00000001 00000002 00000004 00000008 00000010 00000020 00000040 00000080 00000100 00000200 00000400 00000800 00001000 00002000 00004000 00008000 00010000 00020000 00040000 00080000 00100000 00200000 00400000 00800000 01000000 02000000 04000000 08000000 10000000 20000000 40000000 80000000 ST_TEMP_HI ST_TEMP_LOW ST_ROM_CSF ST_FRAM0_WPF ST_FRAM1_WPF * ST_FRAM0_RWE ST_FRAM1_RWE * ST_FRAM0_CSF ST_FRAM1_CSF * ST_FRAM0_ACK ST_FRAM1_ACK * TEMPerature reading too HIgh TEMPerature reading too LOW ROM CheckSum Fail flag FRAM0 Write Protect Fail FRAM1 Write Protect Fail FRAM0 Read/Write Error FRAM1 Read/Write Error FRAM0 CheckSum Fail flag FRAM1 CheckSum Fail flag FRAM0 ACK/data error FRAM1 ACK/data error Flag Name ST_IN_LOCK ST_DIAG_ON ST_FT1_ALM ST_FT2_ALM * ST_FT3_ALM * ST_HART_BOARD * ST_RS232_BOARD * ST_SWITCH_BOARD * ST_EXP0_BOARD ST_EXP1_BOARD ST_EXP2_BOARD ST_EXP3_BOARD ST_FT3_HART * ST_BAD_STATUS ST_STAT_CORR ST_TOTAL_DEATH ST_USER_ALM Definition P.L.L. is IN LOCK DIAGnostics ON 4 to 20 mA output 1 in ALarM 4 to 20 mA output 2 in ALarM 4 to 20 mA output 3 in ALarM whether HART BOARD is fitted whether RS232 BOARD is fitted whether SWITCH BOARD is fitted (reserved for future expansion) (reserved for future expansion) (reserved for future expansion) (reserved for future expansion) HART is in control of its 4 to 20 mA output STATUS register corruption one or more STATus registers have been CORRected status registers not updating - assume the worst User defined variable in alarm

* The status flags marked thus refer to hardware features not present in the 7826. They can safely be ignored.

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Modbus Communications (Transmitter Only)

7826 Insertion Densitometer - Technical Manual

D.6

ESTABLISHING MODBUS COMMUNICATIONS
Using ADView, it is possible to establish which devices are available on the network, and their slave addresses. However, if you are not using ADView, the following procedure can be adopted. If the 7826’s slave address or the values of Registers 47 and 48 are not known, Modbus communications cannot be carried out successfully, and it will be necessary to establish the current values in these items. The following procedure will do this. The process is: (a) Find the slave address by trying all possible values until a response is received. (b) Establish whether the register size is 16 or 32 bits by reading register 48. (c) Find the byte order by reading register 47.

(a) Make sure only the transducer is connected to the Modbus Master, then send the following message (Read Register 47): Slave Address 00 Command Register Address 00 4710 00 02 Checksum

03

checksum

Wait for a response. If there is none, repeat the same message, with the Slave address changed to 1, and await a response. Repeat the process until a response is obtained. This will show the slave address of the transducer.

(b) Send the following message (Read Register 48): Slave Address nn Command Register Address 00 4810 00 02 Checksum

03

checksum

where nn is the transducer's slave address.

The transducer will respond with either: Slave Address nn Command Data Bytes Checksum

03

04

4 data bytes

checksum

showing that the transducer is set to 16 bits register size, or:

Slave Address nn

Command

Data Bytes

Checksum

03

08

8 data bytes

checksum

showing that the transducer is set to 32 bits register size. Thus, by reading the third byte of the response, you can deduce the value of Register 48.

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Modbus Communications (Transmitter Only)

(c) Send the following message (Read Register 47): Slave Address nn Command Register Address 00 4710 00 02 Checksum

03

checksum

where nn is the transducer's slave address.

The transducer will respond with either: Slave Address nn or: Slave Address nn Command Data Bytes Checksum Command Data Bytes Checksum

03

04

4 data bytes

checksum

03

08

8 data bytes

checksum

Examine the first four bytes of the data. If they are all 00, then the transducer is in Big Endian mode; if they are all FF, then the mode is Little Endian.

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Modbus Communications (Transmitter Only)

7826 Insertion Densitometer - Technical Manual

D.7

EXAMPLE OF DIRECT MODBUS ACCESS
In many applications, direct access to Modbus will be unnecessary; ADView provides a way of configuring the 7826, and for accessing individual registers. This example describes how to access the 7826 directly, without the help of ADView. However, before you start, you should configure the transmitter using ADView (described in Chapter 4), and also set the Modbus Byte Order and Register Size (see section D.3.1).

Note:

You can use ADView’s Direct Communications tool to test out the following sequences, or any others you want to try. This has the added advantage that ADView calculates and inserts the checksum value for you.

D.7.1

Example 1: Reading line density (16-bit register size)
The 7826 is assumed to have been configured with Register Size = 16-bit (Register 48 = 0), and has slave address = 1. The following string will read the line density, which is held in Register 257 (010116):

Slave address (hex)

Register address Hi byte

Register address Lo byte

Checksum (Automatically inserted if you are using ADView.)

01 03 01 01 00 02 94 37
Command number: 3 (Read Register) Number of registers to read Hi byte) Number of registers to read Lo byte

The reply from the 7826 will be:

Slave address (hex)

Reply byte count

Checksum

01 03 04 xx xx xx xx cs cs
Line density value as a 32-bit floating point number

Command number: 3 (Read Register)

D.7.2

Example 2: Reading line density (32-bit register size)
The 7826 is assumed to have been configured with Register Size = 32-bit (Register 48 = FFFF16), and has slave address = 1 The following string will read the line density, which is held in Register 257 (010116) Register address Hi byte Checksum Register address Lo byte (Automatically inserted if you are using ADView.)

Slave address (hex)

01 03 01 01 00 01 D4 36
Number of registers to read Hi byte Number of registers to read Lo byte

Command number: 3 (Read Register)

The reply from the 7826 will be the same as for Example 1.

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E
Reference Data
E.1
E.1.1

CONVERSION TABLES
To convert the left hand column of units into the top row of units, multiply by the factor in the box. Length units inches inches yards metres 1 36 39.37 yards 0.0278 1 1.0936 metres 0.0254 0.9144 1

E.1.2

Mass units lb lb ton kg 1 2240 2.2046 ton 4.464E-4 1 9.832E-1 kg 0.4536 1016.05 1

E.1.3

Mass flow units kg/s kg/s kg/h Tonne/h lb/s lb/m lb/h US GPM US BPH
1 0.000277 0.277777 0.4536 0.00756 0.000126 0.0631 x SG 0.0442 x SG

kg/h
3600 1 1000 1632.92 27.215 0.4536 227.12 x SG 158.98 xG

Tonne/h
3.6 0.001 1 1.63296 0.027216 0.000453 0.2271 x SG 0.1589 x SG

lb/s
2.2046 0.000612 0.612384 1 0.016666 0.000277 0.1391 x SG 0.0974 x SG

lb/m
132.28 0.03674 36.74309 60 1 0.016666 8.345 x SG 5.8419 x SG

lb/h
7936.5 2.2046 2204.585 3600 60 1 500.71 x SG 350.5 x SG

US GPM
15.848/SG 0.0044/SG 4.4033/SG 7.1891/SG 0.1198/SG 0.002/SG 1 0.7

US BPH
22.624/SG 0.0063/SG 6.2933/SG 10.267/SG 0.1712/SG 0.0029/SG 1.428571 1

SG = Specific Gravity in g/cc

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Reference Data

E.1.4

Volume flow units lt/m lt/m m /s m /h m /d US GPH US GPM US BPH US BPD
3 3 3 3 m /s

m3/h
0.06 3600 1 0.041666 13.6275 0.227125 0.158987 0.006624

m3/d
1.44 86400 24 1 327.06 5.451 3.8157 0.158987

US GPH
0.004402 264.1717 0.073381 0.003057 1 60 42 1.75

US GPM
0.264171 15850.30 4.402861 0.183452 0.016666 1 0.7 0.029166

US BPH
0.377388 22643.28 6.289802 0.262075 0.023809 1.428571 1 0.041666

US BPD
9.057315 543438.9 150.9552 6.289802 0.571428 34.28571 24 1

1 60000 16.66666 0.694444 227.125 3.785416 2.649791 0.110407

0.000016 1 0.000277 1.16E-5 0.003785 6.31E-5 4.42E-5 1.84E-6

E.1.5

Volume/capacity units in3 in3 ft
3 3

ft3 5.787E-4 1 0.0353 0.0353 0.1357

m3 1.639E-5 2.832E-2 1 0.001 3.785E-3

litres 0.01639 28.32 1000 1 3.785

gal 4.329E-3 7.4805 (US liq) 264.2 (US liq) 0.2642 (US liq) 1

1 1728 6.1024E+4 61.02 231.0

m

litres gal

1 Imperial gallon = 1.20095 U.S. liquid gallons E.1.6 Temperature units °C °C °F Kelvin 1 5/9 x (°F-32) -273.15 °F (°C/5 x 9)+32 1 1 Kelvin +273.15

E.1.7

Pressure units Bar Bar PSI kPa kg/cm
2

PSI 14.5 1 0.145 14.22 0.0193285 100

kPa

kg/cm 1.019716 0.070307 0.009807 1

2

mmHg 750.2 51.737 7.502 735.683 1

1 0.0689476 0.01 0.980665 0.001333

6.89476 1 102.02 0.1333

mmHg

0.0013593

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Reference Data

7826 Insertion Densitometer - Technical Manual

E.1.8

Density units kg/m kg/m3 g/cc lb/ft3 lb/US gal 1 1000 16.0185 119.8264
3

g/cc 0.001 1 0.01602 0.119826

lb/ft3 0.062428 62.428 1 7.4805

lb/US gal 0.008345 8.34543 0.133681 1

E.1.9

Dynamic Viscosity units cP cP Pa.s kgf.s/m
2

Pa.s 0.001 1 9.80665 47.8803 47.8803

kgf.s/m 0.000102 0.101972 1

2

Slug/ftS 0.000021 0.020885

lbf.s/ft2 0.000021 0.020885

1 1000 9806.65 47880.3 47880.3

Slug/ftS lbf.s/ft
2

1 1

1 1

E.1.10

Kinematic Viscosity units cS cS mm /s m /s in /s ft /s cm /s
2 2 2 2 2

mm2/s 1 1 1000000 645.16 2.8944 100

m2/s 1.0E-6 1.0E-6 1 0.000645 0.092864 0.0001

in2/s 0.00155 0.00155 1550 1 144 0.155

ft2/s 0.010765 0.010765 10.7649 0.006944 1 1.0765

cm2/s 0.01 0.01 10000 6.4516 0.928944 1

1 1 1000000 645.16 92.8944 100

Note: The dynamic viscosity (

) of a Newtonian fluid is given by:

dv / dr where = shearing stress between two planes parallel with the direction of flow dv / dr = velocity gradient at right angles to the direction of flow.

The dimensions of dynamic viscosity are M L-1 T-1 and the SI unit is Pascal seconds (Pa s). The kinematic viscosity ( ) is the ratio of the dynamic viscosity to the density The dimensions of kinematic viscosity are L2 T-1 and the SI unit is square metres per second (m2/s).

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7826 Insertion Densitometer - Technical Manual

Reference Data

E.2
E.2.1

PRODUCT DATA
Density/Temperature Relationship of Hydrocarbon Products

Crude Oil
Temp (°C) 60 55 50 45 40 35 30 25 20 15.556 15 10 5 0
3 Density (kg/m )

738.91 742.96 747.00 751.03 755.05 759.06 763.06 767.05 771.03 774.56 775.00 778.95 782.90 786.83

765.06 768.98 772.89 776.79 780.68 784.57 788.44 792.30 796.18 799.57 800.00 803.83 807.65 811.46

791.94 794.93 798.72 802.50 806.27 810.04 813.79 817.54 821.27 824.59 825.00 828.72 832.42 836.12

817.15 820.83 824.51 828.17 831.83 835.48 839.12 842.76 846.38 849.60 850.00 853.61 857.20 860.79

843.11 846.68 850.25 853.81 857.36 860.90 864.44 867.97 871.49 874.61 875.00 878.50 882.00 885.49

869.01 872.48 875.94 879.40 882.85 886.30 889.73 893.16 896.59 899.62 900.00 903.41 906.81 910.21

894.86 898.24 901.80 904.96 908.32 911.67 915.01 918.35 921.68 924.63 925.00 928.32 931.62 934.92

920.87 923.95 927.23 930.50 933.76 937.02 940.28 943.52 946.77 949.64 950.00 953.23 958.45 959.66

946.46 949.63 952.82 956.00 959.18 962.36 965.53 968.89 971.85 974.65 975.00 978.15 981.29 984.42

Refined Products
Temp. (°C) 60 55 50 45 40 35 30 25 20 15.556 15 10 5 0
3 Density (kg/m )

605.51 610.59 615.51 620.49 625.45 630.40 635.33 640.24 645.13 649.46 650.00 654.85 659.67 664.47

657.32 662.12 666.91 671.68 676.44 681.18 685.92 690.63 695.32 699.48 700.00 704.66 709.30 713.92

708.88 713.50 718.11 722.71 727.29 731.86 736.42 740.96 745.49 749.50 750.00 754.50 758.97 763.44

766.17 769.97 773.75 777.53 781.30 785.86 788.81 792.55 796.28 799.59 800.00 803.71 807.41 811.10

817.90 821.49 825.08 828.67 832.24 835.81 839.37 842.92 846.46 849.61 850.00 853.53 857.04 860.55

868.47 872.00 875.53 879.04 882.56 886.06 889.56 893.04 896.53 899.61 900.00 903.47 906.92 910.37

918.99 922.46 925.92 929.38 932.84 938.28 939.72 943.16 846.58 949.62 950.00 953.41 956.81 960.20

969.45 972.87 976.28 979.69 983.09 986.48 989.87 993.26 996.63 999.63

1019.87 1023.24 1026.60 1029.96 1033.32 1038.67 1040.01 1043.35 1046.68 1049.63

1000.00 1050.00 1003.36 1053.32 1006.72 1056.63 1010.07 1059.93

The above tables are derived from equations which form the basis of the data in the Revised Petroleum Measurement Tables (IP 200, ASTM D1250, API 2540 and ISO R91 Addendum 1).

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Reference Data

7826 Insertion Densitometer - Technical Manual

The density temperature relationship used is:
t 15 exp 15 t 1 0.8 15 t

where:
t 15 t 15

= Density at line temperature t°C (kg/m3) = Density at base temperature 15°C (kg/m3) = ( t -15 )°C (i.e., t - base temperature) = Tangent thermal expansion coefficient per °C at base temperature 15°C

The tangent thermal expansion coefficient differs for each of the major groups of hydrocarbons. It is obtained using the following relationship:
15

K0

K 1 15
15 2

where K0 and K1 are the API factors and are defined below:
Product Crude Oil Gasolines Kerosines Fuel Oils Density Range (kg/m )
3

K0

K1

771 - 981 654 - 779 779 - 839 839 - 1075

613.97226 346.42278 594.54180 186.96960

0.00000 0.43884 0.00000 0.48618

E.2.2

Platinum Resistance Law (To DIN 43 760) °C Ohms °C Ohms °C Ohms °C Ohms °F Ohms °F Ohms

-50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0

80.31 82.29 84.27 86.25 88.22 90.19 92.16 94.12 96.09 98.04 100.00

5 10 15 20 25 30 35 40 45 50 55

101.91 103.90 105.85 107.79 109.73 111.67 113.61 115.54 117.47 119.40 121.32

60 65 70 75 80 85 90 95 100 105 110

123.24 125.16 127.07 128.98 130.89 132.80 134.70 136.60 138.50 140.39 142.29

115 120 125 130 135 140 145 150 155 160 165

144.17 146.06 147.94 149.82 151.70 153.58 155.45 157.31 159.18 161.04 162.90

0 10 20 30 32 40 50 60 70 80 90

93.03 95.21 97.39 99.57 100.00 101.74 103.90 106.07 108.23 110.38 112.53

100 110 120 130 140 150 160 170 180 190 200

114.68 116.83 118.97 121.11 123.24 125.37 127.50 129.62 131.74 133.86 135.97

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Reference Data

E.2.3

Density of Ambient Air (in kg/m ) Air Pressure (mb) 6 10 Air Temperature (°C) 14 18 22 26 30

3

900 930 960 990 1020

1.122 1.159 1.197 1.234 1.271

1.105 1.142 1.179 1.216 1.253

1.089 1.125 1.162 1.198 1.234

1.073 1.109 1.145 1.180 1.216

1.057 1.092 1.128 1.163 1.199

1.041 1.076 1.111 1.146 1.181

1.025 1.060 1.094 1.129 1.163

Taken at a relative humidity of 50%
E.2.4 Density of Water (in kg/m to ITS - 90 Temperature Scale) Temp °C 0 20 40 60 80 100 0 2 4 6 8 10 12 14 16 18
3

999.840 999.940 999.972 999.940 999.848 999.699 999.497 999.244 998.943 998.595 998.203 997.769 997.295 996.782 996.231 995.645 995.024 994.369 993.681 992.962 992.212 991.432 990.623 989.786 988.922 988.030 987.113 986.169 985.201 984.208 983.191 982.150 981.086 980.000 978.890 977.759 976.607 975.432 974.237 973.021 971.785 970.528 969.252 967.955 966.640 965.305 963.950 962.577 961.185 959.774 958.345

Use pure, bubble-free water.

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Electrical Installation for older equipment

F Electrical Installation for older equipment
F.1 INTRODUCTION
This appendix has details of the older version of 7826, which had 12 terminals (Figure F.1), and also gives details of the connections to the older Solartron? signal processing equipment for both the 8-terminal and 12-terminal version of 7826. Note: Section 3 gives details of the electrical connections for the current version of 7826.

WARNING: Electricity is dangerous and can kill. Disconnect the power (from signal processing equipment) before making any connections.

The 7826 transducer can be operated in two general environments, either in SAFE AREAS or in HAZARDOUS AREAS. When the 7826 transducer is installed in hazardous areas: Refer to safety instruction booklet 78265061/SI for compliance with safety matters. Safety barriers or galvanic isolators are not required. However, signal converters and flow computers are not intrinsically safe, and MUST only be operated in a safe area.

T1 PWR+ T2 PWRT3 PWR+ T4 PWRT5 T6

T7 PRT+ T8 SIG+ T9 SIGT10 PRTT11 T12

78260152A
OUTPUTS

Figure F.1 The 12-terminal connections of earlier 7826

DENS

VISC.

TEMPERATURE

I.S.ONLY POWER SUPPLY NON I.S.+Exd POWER SUPPLY VISCOSITY RANGE

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Electrical Installation for older equipment

7826 Insertion Densitometer - Technical Manual

F.2

CONNECTIONS TO OLDER SOLARTRON? EQUIPMENT
7915 Flow Computer 7826 Transducer
Ch.1 Supply + Sig + Sig Supply PRT Pwr + PRT Sig + PRT Sig PRT Pwr 1 3 4 2 5 6 7 8 PL1/1 PL6/1 PL6/2 PL1/2 PL2/7 PL7/7 PL7/8 PL2/8 Ch.2 PL1/3 PL6/3 PL6/4 PL1/4 PL2/9 PL7/9 PL7/10 PL2/10 Ch.3 PL1/5 PL6/5 PL6/6 PL1/6 Ch.4 PL1/7 PL6/7 PL6/8 PL1/8 Density/Base Density Power + Density /Base Density input + Density/Base Density input Density/Base Density power PRT PWR + PRT input + PRT input PRT PWR -

PL9/1 PL9/2

Chassis Earth Chassis Earth

Figure F.2 Typical 7826 (8-terminals) to 7915 Flow Computer (SAFE AREA)

7925/45 Signal Converter 7826 Transducer
Supply + Sig + Sig Supply PRT Pwr + PRT Sig + PRT Sig PRT Pwr 1 3 4 2 5 6 7 8 PL1/1 PL1/2 PL1/3 PL1/4 PL2/7 PL2/8 PL2/9 PL2/10 Density PWR + Density Signal + Density Signal Density PWR P.R.T. PWR + P.R.T. Signal + P.R.T. Signal P.R.T. PWR -

PL12/2

Chassis Earth

Figure F.3 Typical 7826 (8-terminals) to 7925/46 Signal Converter (SAFE AREA)

7926/46 Signal Converter 7826 Transducer
Supply + Sig + Sig Supply PRT Pwr + PRT Sig + PRT Sig PRT Pwr 1 3 4 2 5 6 7 8 TB9/5 TB9/6 TB9/7 TB9/8 TB11/5 TB11/6 TB11/7 TB11/8 Density PWR + Density Signal + Density Signal Density PWR P.R.T. PWR + P.R.T. Signal + P.R.T. Signal P.R.T. PWR -

TB2/2

Chassis Earth

Figure F.4 Typical 7826 (8-terminals) to 7926/46 Signal Converter (SAFE AREA)

F-2

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7826 Insertion Densitometer - Technical Manual

Electrical Installation for older equipment

7915 Flow Computer 7826 Transducer
Ch.1 Non I.S. Power Supply + Density Output 3 12 PL1/1 PL6/1 PL6/2 Non I.S. Power Supply PRT Pwr + PRT Sig + PRT Sig PRT Pwr 4 7 8 9 10 PL1/2 PL2/7 PL7/7 PL7/8 PL2/8 Ch.2 PL1/3 PL6/3 PL6/4 PL1/4 PL2/9 PL7/9 PL7/10 PL2/10 Ch.3 PL1/5 PL6/5 PL6/6 PL1/6 Ch.4 PL1/7 PL6/7 PL6/8 PL1/8 Density/Base Density Power + Density /Base Density input + Density/Base Density input Density/Base Density power PRT PWR + PRT input + PRT input PRT PWR -

PL9/1 PL9/2

Chassis Earth Chassis Earth

Figure F.5 Typical 7826 (12-terminals) to 7915 Flow Computer (SAFE AREA)

7925/45 Signal Converter 7826 Transducer
Non I.S. Power Supply + Density Output 3 12 PL1/1 PL1/2 PL1/3 Non I.S. Power Supply PRT Pwr + PRT Sig + PRT Sig PRT Pwr 4 7 8 9 10 PL1/4 PL2/7 PL2/8 PL2/9 PL2/10 Density PWR + Density Signal + Density Signal Density PWR P.R.T. PWR + P.R.T. Signal + P.R.T. Signal P.R.T. PWR -

PL12/2

Chassis Earth

Figure F.6 Typical 7826 (12-terminals) to 7925/45 Signal Converter (SAFE AREA)

7926/46 Signal Converter 7826 Transducer
Non I.S. Power Supply + Density Output 3 12 TB9/5 TB9/6 TB9/7 Non I.S. Power Supply PRT Pwr + PRT Sig + PRT Sig PRT Pwr 4 7 8 9 10 TB9/8 TB11/5 TB11/6 TB11/7 TB11/8 Density PWR + Density Signal + Density Signal Density PWR P.R.T. PWR + P.R.T. Signal + P.R.T. Signal P.R.T. PWR -

TB2/2

Chassis Earth

Figure F.7 Typical 7826 (12-terminals) to 7926/46 Signal Converter (SAFE AREA)

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Electrical Installation for older equipment

7826 Insertion Densitometer - Technical Manual

F.3

7826 12-Terminal Connections to Customer’s Equipment
The power supply requirements on the customer’s own equipment are: For density transducer: For PRT: 21.6 to 26.4Vdc, 25mA maximum 5mA dc maximum

The electrical connections are shown in Figure F.8.

CAUTION: Incorrect connection can damage the instruments.

Power Supply +ve Power Supply -ve

T1 PWR+ T2 PWRT3 PWR+ T4 PWRT5 T6

T7 PRT+ T8 SIG+ T9 SIGT10 PRTT11 T12

PRT Supply +ve PRT Signal +ve PRT Signal -ve PRT Supply -ve

78260152A
OUTPUTS

VISC.

TEMPERATURE

DENS

Figure F.8 7826 12-terminal connections to customer’s own equipment

I.S.ONLY POWER SUPPLY NON I.S.+Exd POWER SUPPLY VISCOSITY RANGE

Density Signal +ve

Density Signal ive

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7826 Insertion Densitometer - Technical Manual

4-20mA Direct Density Output Version

G
4-20mA Direct Density Output Version
G.1 INTRODUCTION
The 4-20mA version is an earlier 7826 Insertion Densitometer that provides an analog output, which is a direct measure of liquid density. The loop-powered 4-20mA transmitter replaces the user connect board in the standard unit and provides a calibrated and temperature compensated linear density output with switch selectable ranges. The transducer is calibrated during manufacture using onboard trimpots. Where local conditions require conformance to the 89/336/EEC Electromagnetic Compatibility Directive (amended by 92/31/EEC and 93/68/EEC), a 7826A Filter Box is required (see section G.3.2).

G.2

DENSITY RANGE SETTING
The basic density range is set by adjusting two banks of switches, one for the minimum density value and one for the maximum. Figure G.1 shows the positions of the trimpots RV1 - RV4 and switches SW1 - SW3 on the PCB.

Figure G.1 The 4-20mA PCB Layout
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4-20mA Direct Density Output Version

7826 Insertion Densitometer - Technical Manual

Figure G.1 shows the switch positions, and their corresponding density range settings in kg/m3. Switch SW1 sets the 4mA density value, and Switch SW2 sets the 20mA density value. Table G.1 Density Range Switch Positions Switch 1 (min. value) Position 1 2 3 4 5 6 7 8 Density (kg/m3) 0 700 800 900 1000 1100 1200 1300 Switch 2 (max. value) Position 1 2 3 4 5 6 7 8 Density (kg/m3) 100 800 900 1000 1100 1200 1300 1400

The minimum and maximum points are entirely independent of each other. For example, possible ranges would include: 0 - 100 kg/m3 0 - 1400 kg/m3 700 - 900 kg/m3 1100 - 1400 kg/m3 G.2.1 50kg/m3 offset switch Switch SW3 will add 50 kg/m3 to the minimum and maximum values set on switches SW1 and SW2 (see Figure G.1). For example, the range 700 - 900 kg/m3 would become 750 - 950 kg/m3 after changing switch SW3. All spans are in steps of 100 kg/m3; switch SW3 cannot be used to give a span of only 50 kg/m3. G.2.2 Out-of-range behaviour If the density lies outside the set range, the current output will remain at the upper or lower limit; there is no over range indication. If the transducer stops oscillating, the converter will remain at the top of its range continuing to output 20mA. For example, if the selected range was 750 to 850 kg/m3 and the fluid drained away leaving the fork in air, the transducer would indicate 750 kg/m3. If the fork was then placed in water with a density of 1000 kg/m3, the transducer would measure only 850 kg/m3. (Useful for 1.2 kg/m3 air check) (Maximum possible span) (Typical petroleum products)

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7826 Insertion Densitometer - Technical Manual

4-20mA Direct Density Output Version

G.3
G.3.1

ELECTRICAL INSTALLATION
Non-EMC installation There are only four external connections to the 7826 when the 4-20mA PCB is fitted. The unit should be connected to a supply of between 24 and 27V dc at 70mA. It is recommended that the unit is connected as in Figure G.2a where the unit sources the 4-20mA.

Note:

To ensure correct operation, the voltage between terminals 2 and 3 should not be less than 12V at any time.

4 3

+24V DC

+ve

4-20mA +ve 4-20mA Meter/Density Converter 4-20mA ve +

2 1 7826 4-20mA Terminal Block

0V DC

ve

+24V PSU

Figure G.2a The 4-20mA Electrical Installation (7826 Sourcing Current) If desired, the unit may be connected so that it will sink the 4-20mA instead of sourcing it (see Figure G.2b). This is an alternative arrangement to the one shown in Figure G.2a; either circuit may be used, depending on your application.

4 3

+24V DC

+ve

4-20mA +ve

+ 4-20mA Meter/Density Converter ve

2 1 7826 4-20mA Terminal Block

4-20mA -ve

0V DC

+24V PSU

Figure G.2b The 4-20mA Electrical Installation (7826 Sinking Current)

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7826 Insertion Densitometer - Technical Manual

Note:

Some early units (issue ‘A’ PCBs) had only three terminals, which should be connected as in Figure G.2c. In this case, the unit will only sink the 4-20mA and will not source it.

2 3

+24V DC

+ve

4-20mA +ve

+ 4-20mA Meter/Density Converter ve

1 7826 4-20mA Terminal Block

Common

+24V PSU

Figure G.2c Issue ‘A’ PCB Electrical Installation

G.3.2

EMC installation The 7826 2A Filter box is required whenever the 4-20mA output version of the 7826 is used where local conditions require conformance to the 89/336/EEC Electromagnetic Compatibility Directive, (amended by 92/31/EEC & 93/68/EEC). It is not required for a 7826 with direct (frequency) output, or where EMC conformance is unnecessary. The 2A Filter is housed in an explosion-proof container approximately 137mm x 137mm x 78mm (5.4in x 5.4in x 3.1in) - see Figure G.3a and Figure G.3b - and can be used in safe or hazardous areas. It is rated to EEx d IIB T6. Connections are made via terminal blocks contained on the printed circuit board within the housing, and to a ground connection on the exterior of the container. Mechanical Installation The 2A Filter box must be less than 1 metre (39.37 inches), from its associated 7826 transducer. Figure G.3a shows the fixing dimensions. The filter housing can be mounted in any orientation on any suitable surface, provided that the environmental specification is not exceeded. (For instance, do not mount it on a hot surface without suitable thermal insulation). Cable entry is via cable glands, for which two tapped holes are provided on opposite sides of the filter. To gain access to the terminal blocks, the top plate must be unscrewed from the main housing. (Remove the hexagonal locking bolt first).

CAUTION: The filter must not be opened in the presence of a flammable atmosphere, even when un-powered.

The unit is sealed with an O-ring, which must be retained for re-use. If it is damaged in any way, it must be replaced.

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7826 Insertion Densitometer - Technical Manual

4-20mA Direct Density Output Version

Figure G.3a Plan view of 7826 2A Filter

Figure G.3b Side view of 7826 2A Filter

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4-20mA Direct Density Output Version

7826 Insertion Densitometer - Technical Manual

G.3.3

Electrical Installation The length of the cable between the 2A Filter box and its associated 7826 must be less than 1 metre (39.37 inches). The power supply to the 2A Filter (and hence to the 7826) should be 24 to 27V dc, capable of supplying at least 70mA. The Filter housing must also be connected to a suitable safety earth, using the screw terminal on the outside of the filter housing. It is recommended that the connections are made using a suitable 4-core instrumentation cable with an overall screen to cover all cores. Where permissible, the screen should be connected to earth at both ends. Note that for intrinsic safety, termination of the screen to earth in the hazardous area is NOT generally permitted. In hazardous areas, the connections must be taken through suitably-rated cable glands and adapters, as follows: EExd lB or IIC-rated cable gland. M20 x 1.5 EExd IIB or IIC-rated thread adapter (if required). If either of the tapped holes is unused, it must be blanked using a suitable IIB- or IIC- rated blanking plug. All connections are made to two terminal blocks on the circuit board within the filter, as shown below.

Figure G.4 Filter box circuit board layout

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7826 Insertion Densitometer - Technical Manual

4-20mA Direct Density Output Version

Connections to the filter are shown below for three different configurations:

Figure G.5a 4-20mA Electrical Installation using 2A Filter (7826 sourcing current)

Figure G.5b 4-20mA Electrical Installation using 2A Filter (7826 sinking current)

Figure G.5c ‘Issue A’ PCB (3-terminal) 4-20mA Electrical Installation using 2A Filter
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4-20mA Direct Density Output Version

7826 Insertion Densitometer - Technical Manual

G.4

CALIBRATION
The 7826 Insertion Liquid Density Transducer is calibrated within the standard shroud against a transfer standard instrument traceable to International Standards prior to leaving the factory. The transducer is calibrated over the density range 750 to 850 kg/m3. However, the precision of the transducer has a minor dependency on the fork installation, and a minor adjustment may be required on site. Factory Calibration Procedure The transducer is cleaned and dried and resonated in air at 20°C. The 0 - 100 kg/m3 range is selected on the internal switches, and the output adjusted to read 4.192mA (representing 1.2 kg/m3) using the zero trim pot RV1. The transducer is then placed in a fluid of known density, and the appropriate density range is selected on the internal switches. The span is set to 100 kg/m3. The scale trimpot RV2 is then adjusted so that the correct output current is obtained for the fluid density (see Example 1). The transducer is over-checked in a second fluid of known density.

G.4.1

In-line calibration Since the calibration of the transducer is influenced by the dimensions of the cavity into which it is placed, it will be necessary to perform an ‘in-line’ calibration if the cavity is different to the ‘standard pocket’ and full accuracy is required. It is also recommended that if the installation tolerances detailed in Chapter 2 cannot be achieved, an ‘in-line’ calibration is carried out each time the transducer is installed. To perform an ‘in-line’ calibration, it is necessary to know the exact density of the calibrating fluid at the calibrating conditions. The fluid density at these conditions may be determined by using one of the methods outlined in Chapter 5. The transducer may be calibrated as follows: 1. The zero trimpot RV1 should not need adjustment. However, a check should be made to ensure that the output current when the transducer is resonating in air is 4.192mA (representing 1.2 kg/m3) when the range switches are set to 0 - 100 kg/m3. If the reading is in error by more than ±0.1mA, reset the output using the zero trimpot RV1. 2. Place the transducer in-line under operating conditions, and allow the transducer to temperature stabilise. Ensure that there is no entrained air within the process fluid. 3. Check the density of the calibration fluid at the line conditions. 4. Set the density range on the internal switches to cover the process fluid density range. Set the span to 100kg/m3. 5. Adjust the scale trimpot RV2 until the correct current output is obtained to represent the actual fluid density.

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7826 Insertion Densitometer - Technical Manual

4-20mA Direct Density Output Version

Example 1: To Check Transducer Output
3 Assume that the process density is 876.20 kg/m . The density select switches are set to the range 3 800 - 900 kg/m giving a transducer sensitivity of 0.16mA/kg/m3. The output obtained from the transducer is 15.26mA.

The required output is given by: Io = = = Where: Io
A min

[( A — min)S] + 4 [(876.20 - 800) 0.16 +4] ±0.2mA 16.19 ±0.2mA Output Current (mA) Actual Density (kg/m3) Minimum Density Range (kg/m3) Transducer Sensitivity (kg/m3)

= = = =

S

The transducer is therefore out of specification and trimpot RV2 should be adjusted until an output of 16.19mA is obtained. Example 2: To Check Transducer Indicated Density Assume that the output from the transducer is 7.23mA, and that the line density is 1270.0 kg/m3. The density select switches are set to the range 1250 - 1350 kg/m3. The indicated density is given by:

I0
I

4 S
min

7.23 0.16

4

1250

1270.19kg / m 3

The transducer is therefore indicating the correct density. G.4.2 Out-of-range calibration The 4 and 20mA limits should not require calibration, but they can easily be checked and adjusted if necessary using the following procedure: 1. Place the transducer in a fluid with a density between 100 and 1350 kg/m3. This may be the product normally being measured by the transducer or any other fluid. 2. Set the density range switches to any range above the actual fluid density. 3. The output current should now read exactly 4mA. If it does not, then RV4 may be adjusted until 4mA is obtained. 4. Set the density range switches to any range below the actual fluid density. 5. The output current should now read exactly 20mA. If it does not, then RV3 may be adjusted until 20mA is obtained.

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7826 Insertion Densitometer - Technical Manual

G.5
G.5.1

7826 4-20MA OUTPUT VERSION SPECIFICATION
Performance Density accuracy: ±2 kg/m3 ±5 kg/m3 ±5 kg/m Repeatability: Stability: Fork temperature range: Housing temperature range: Temperature effect:
3

(750 — 1250 kg/m3) (0 - 750kg/m3) (1250 — 1450 kg/m3)
3

±0.5 kg/m ±1 kg/m
3

-50 to +160°C -40 to +85°C° 0 to +60°C ±0.1 kg/m /°C ±0.15 kg/m /°C ±0.15 kg/m3/°C
3 3

-50 to +160°C ±0.2 kg/m3/°C ±0.25 kg/m /°C ±0.25 kg/m3/°C
3

(750 — 1250 kg/m3) (0 - 750kg/m3) (1250 — 1450 kg/m3)

Electronics temperature range: Electronics temperature effect:

-40 to +85°C
3 ±0.02 kg/m /°C

G.5.2

Power supplies Fork: 4 - 20mA loop: 24-27Vdc at 70mA 12 - 30Vdc

G.5.3

Environment Rating: Safety: IP65 Transducer designed to be explosion-proof to a maximum specification of EEx d IIC Filter box designed to be explosion-proof to a maximum specification of EEx d IIB

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Returns Forms
The forms contained in this appendix, must be copied and completed whenever the 7826 Insertion Densitometer is to be returned for servicing, calibration or repair to Mobrey Measurement or one of their agents. This must be done before the product is shipped. The purpose of the form is to inform Mobrey Measurement of any potentially hazardous chemicals that may be present on the 7826.

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7826 Insertion Densitometer - Technical Manual

Returns Forms

Innovative Service Solutions
Customer Equipment - Returns Form - Slough - 2006
Customer Name: Customer Address:
Post / Area Code:

Contact Name: Telephone Number: Fax Number: Email Address: Customer Order Reference No: Mobrey ( Solartron ) - Unit Type: Serial Number: 'X'

Please state the reason for the return of the equipment: Fixed Price Repair & Test Fixed Price Repair & Calibration Fixed Price Calibration Credit / Return to Stock Support Group Investigation Repair Fault Details:

Warranty Repair & Test Warranty Repair & Cal Contract Repair & Cal Contract Calibration Contract No

If Warranty - Application: If Warranty - Process Conditions: Health And Safety Declaration. The Control of Substances Hazardous To Health Regulations 1988. YES Has the above equipment been exposed NO to Hazardous Substances Or Materials ? 'X'
If 'NO' Please attach this form to your equipment and ship to the

address below.
If 'YES' Please complete the sheet 2 Health and Safety Declaration form.

Mobrey Ltd, Customer Service Department, 158 Edinburgh Avenue, Slough, Berkshire, SL1 4UE, England, UK. Telephone: + 44 (0) 1753 756600 Fax: + 44 (0) 1753 787134 Email: dob.cherriman@emersonprocess.com FAO: Mr Dob Cherriman Customer Signature: Position:

Date:

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7826 Insertion Densitometer - Technical Manual

Innovative Service Solutions
Health And Safety Declaration
The Control of Substances Hazardous to Health Regulations 2002 It is a requirement that all equipment returned to Mobrey Ltd for any purpose be certified by the sender as "SAFE TO HANDLE". You are required to identify any substances or materials that the above mentioned equipment has or could have been exposed to since it left the factory. If any unit is likely to be contaminated with blood, bodily fluids, pathological specimens, other biohazards, chemicals or substances hazardous to health or any other hazard, it must where practicable be decontaminated prior to return for service repair. Mobrey Ltd reserve the right to refuse to handle material which we feel could pose a risk to our service support staff even after decontamination. DETAILS OF HAZARDOUS SUBSTANCES OR MATERIALS
Common name of material or substance the equipment has been exposed to:

Chemical name or formula of the material or substance the equipment has been exposed to:

WHAT IS THE HAZARD ASSOCIATED WITH THE ABOVE: FLAMMABLE EXPLOSIVE TOXIC IRRITANT CORROSIVE IS THE HAZARD BY: SKIN CONTACT INGESTION 'X' INHALATION MICRO -ORGANISM HARMFUL OTHER - PLEASE SPECIFY

'X'

GIVE DETAILS OF "OCCUPATIONAL EXPOSURE LIMITS (OEL) or MAXIMUM EXPOSURE LIMITS (MEL) SPECIFY ANY SPECIAL HANDLING REQUIREMENTS:
CONFIRMATION

Customer Signature: Position:

Date:

Mobrey Ltd, Customer Service Department, 158 Edinburgh Avenue, Slough, Berkshire, SL1 4UE, England, UK. Telephone: + 44 (0) 1753 756600 Fax: + 44 (0) 1753 787134 Email: dob.cherriman@emersonprocess.com FAO: Mr Dob Cherriman

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Technical Manual

Solartron? 7826

78265004 September 2006

Mobrey, Mobrey Measurement, and the Mobrey logotype are registered trademarks of Mobrey Limited. The Emerson logo is a trade mark and service mark of Emerson Electric Co. Solartron? is a registered trademark of Lloyd Instruments Limited, a subsidiary of Ametek, Inc. All other marks are the property of their respective owners.

Mobrey Measurement 158 Edinburgh Avenue, Slough, Berks, UK, SL1 4UE T +44 (0) 1753 756600 F +44 (0) 1753 823589 mobrey.sales@EmersonProcess.com www.mobrey.com

Mobrey Inc 19408 Park Row, Suite 320, Houston, TX 77084 USA T +281 398 7890 F +281 398 7891 mobrey.sales@EmersonProcess.com www.mobrey.com

Mobrey SA-NV Mobrey GmbH Mobrey SA Mobrey sp z o o Mobrey AB

Belgium Deutschland France Polska Sverige

tel: 02/465 3879 tel: 0211/99 808-0 tel: 01 30 17 40 80 tel: 022 871 7865 tel: 08-725 01 00

? 2006, Mobrey. The right is reserved to amend details given in this publication without notice.


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