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A Guide to the Specification and Procurement of Industrial Process Weighing Systems Guide to the Specification and Procurement of Industrial Process Weighing Systems


1
A Guide to the
Specification and Procurement
of
Industrial Process Weighing Systems
The Institute of Measurement and Control
87 Gower Street
London
WC1E 6AA
ISBN 0 904457 32 X Published 2000 Guide to the Specification and Procurement of Industrial Process Weighing Systems


2
COMMITTEE RESPONSIBLE FOR THIS GUIDE
The Weighing Group reporting to the Measurement Science & Technology Panel has
prepared this
Institute of Measurement and Control Guide.
The persons listed below served as members of the Weighing Group in preparing this Guide.
Professor U Erdem (Chairman)
Procon Engineering Ltd.
P Zecchin (Deputy Chairman)
Nobel Systems Ltd.
J. Anthony
UK Weighing Federation
A Bowen
Kvaerner Davy Weighing Systems
G Cabral
CEL International Ltd.
D Green
DCG Associates
A Knott
National Physical Laboratory
C Marklew
Aston Dane Ltd.
A Urwin
Quality Scheme for Ready Mixed Concrete
Professor J Pugh
Glasgow Caledonian University
J Webb
Avery Berkel
C Whittingham
British Steel, Scunthorpe
The Group would like to extend special thanks to the Secretariat of the Institute of
Measurement and Control for their support throughout the project, and to Debbie Bilham of
Nobel Systems Ltd. for the preparation of the drawings.
The Guide is subject to review at any time by the responsible technical group of the Institute.
The Institute welcomes all comments on this document and requests that these be addressed
to the Institute.
Users of this Institute of Measurement and Control Guide shall be responsible for its correct
application.
No part of this publication may be reproduced in any form without the prior permission in writing of
The Institute of Measurement and Control.
Publication Reference Number: WGC1099
British Library Cataloguing in Publication data.
A catalogue for this book is available from the British Library.
ISBN: 0 904457 32X Guide to the Specification and Procurement of Industrial Process Weighing Systems


3
CONTENTS
PAGE
1
.
FOREWORD
6
2.
SCOPE
7
3.
TERMS AND DEFINITIONS
8
4.
GENERAL CONSIDERATIONS
11
4.1
HUMAN FACTORS...................................................................................................................................... 11
4.1.1
Design and installation
11
4.1.2
Calibration, adjustment, and maintenance
12
4.1.3
Training of personnel
12
4.1.4
Access to the system by untrained personnel
12
4.2
FACTORS RELATING TO THE SELECTION OF LOAD CELLS ....................................................... 12
4.2.1
Number of load cells
12
4.2.2
Type of load cells
13
4.2.3
Capacity of load cells
13
4.2.4
Use of dummy load cells as pivots
13
4.3
MULTIPLE LOAD CELL APPLICATIONS ............................................................................................. 14
4.3.1
Combination of load cell errors
14
4.3.2
Influence of the rated load output and output resistance
14
4.4
CALIBRATION............................................................................................................................................. 15
4.4.1
Use of standard weights
16
4.4.2
Use of reference weights
16
4.4.3
Use of substitute material
17
4.4.4
Use of force transfer method
17
4.4.5
Use of metered flow
17
4.4.6
Use of proving tanks
18
4.4.7
Use of technique remote to the weighing installation
18
4.4.8
Calibration of weighing system components
18
4.5
SYSTEM PERFORMANCE......................................................................................................................... 19
4.5.1
Terminal line
19
4.5.2
Best straight line through zero
20
4.5.3
Error specifications based on OIML R76 (BS EN 45 501)
21
4.6
CLEANING AND HYGIENE....................................................................................................................... 23
5.
SPECIFIC CONSIDERATIONS
24
5.1
TEMPERATURE .......................................................................................................................................... 24
5.1.1
Load receiving element
24
5.1.2
Load cell
26
5.1.3
Mounting hardware
28
5.1.4
Load bearing structure
28
5.1.5
Junction box and cable
28
5.1.6 Signal
processor
30
5.2 ATMOSPHERIC
QUALITY........................................................................................................................ 30
5.2.1
Load receiving element
31
5.2.2
Load cell
31
5.2.3
Mounting hardware
31
5.2.4
Load bearing structure
31
5.2.5
Junction box
31
5.2.6
Signal processor
31 Guide to the Specification and Procurement of Industrial Process Weighing Systems


4
5.3
HUMIDITY.................................................................................................................................................... 32
5.3.1
Load receiving element
32
5.3.2
Load cell
33
5.3.3
Mounting hardware
33
5.3.4
Load bearing structure
34
5.3.5
Junction box
34
5.3.6
Signal processor
34
5.4
PRECIPITATION ......................................................................................................................................... 34
5.4.1
Load receiving element
34
5.4.2
Load cell
35
5.4.3
Mounting hardware
35
5.4.4
Load bearing structure
36
5.4.5
Junction box and cables
36
5.4.6
Signal processor
36
5.5
WIND LOADING ......................................................................................................................................... 36
5.5.1
Load receiving element
37
5.5.2 Load
cells
39
5.5.3
Mounting hardware
40
5.5.4
Load bearing structure
40
5.5.5
Junction box
40
5.5.6
Signal processor
40
5.6
IMPACT ......................................................................................................................................................... 42
5.6.1
Load receiving element
44
5.6.2
Load cell
45
5.6.3
Mounting hardware
45
5.6.4
Load bearing structure
45
5.6.5
Junction box
45
5.6.6
Signal processor
45
5.7
VIBRATION .................................................................................................................................................. 46
5.7.1
Load receiving element
48
5.7.2
Load cell
48
5.7.3
Mounting hardware
48
5.7.4
Load bearing structure
49
5.7.5 Junction
box
49
5.7.6
Signal processor
49
5.8
STRUCTURAL INTERACTION................................................................................................................. 49
5.8.1
Load receiving element
49
5.8.2
Load cell
50
5.8.3
Mounting hardware
51
5.8.4
Load bearing structure
51
5.8.5
Junction box
51
5.8.6
Signal processor
51
5.9
HORIZONTAL RESTRAINING DEVICES............................................................................................... 52
5.9.1
Load receiving element
53
5.9.2
Load cell
54
5.9.3
Mounting hardware
54
5.9.4
Load bearing structure
54
5.9.5
Junction box
54
5.9.6
Signal processor
54
5.10
PIPEWORK ................................................................................................................................................... 55
5.10.1
Load receiving element
58
5.10.2
Load Cell
59
5.10.3
Mounting hardware
59
5.10.4
Load bearing structure
59
5.10.5
Junction box
59
5.10.6
Signal processor
59 Guide to the Specification and Procurement of Industrial Process Weighing Systems


5
6.
SPECIAL CONSIDERATIONS
60
6.1
HAZARDOUS AREA WEIGHING SYSTEMS.......................................................................................... 60
6.1.1
Load receiving element
61
6.1.2
Load cell
62
6.1.3
Mounting hardware
63
6.1.4
Load bearing structure
63
6.1.5
Junction box and cable
63
6.1.6
Signal processor
64
6.2
ELECTRICAL STORMS AND EARTHING ............................................................................................. 65
6.3
SEISMIC LOADS.......................................................................................................................................... 66
6.4
RADIATION .................................................................................................................................................. 68
7.
ANNEXES
69
7.1
WEIGHING SYSTEMS SUBJECT TO LEGISLATION.......................................................................... 69
7.1.1
Intro