1、BRITISH STANDARD BS 7405:1991 Incorporating Amendment No. 1 Guide to Selection and application of flowmeters for the measurement of fluid flow in closed conduitsBS7405:1991 This British Standard, having been prepared under the directionof the Industrial-process Measurement and Control Standards Poli
2、cy Committee, waspublished under the authorityof the Standards Boardand comes intoeffecton 30 August1991 BSI 03-2000 The following BSI references relate to the work on this standard: Committee reference PCL/2 Draft for comment 87/28970DC ISBN 0 580 19335 7 Committees responsible for this British Sta
3、ndard The preparation of this British Standard was entrusted by the Industrial-process Measurement and Control Standards Policy Committee (PCL/-) to Technical Committee PCL/2, upon which the following bodies were represented: British Compressed Air Society British Gas plc Department of Energy (Gas a
4、nd Oil Measurement Branch) Department of Trade and Industry (National Engineering Laboratory) Electricity Supply Industry in United Kingdom Energy Industries Council GAMBICA (BEAMA Ltd.) Institute of Measurement and Control Institute of Petroleum Institute of Trading Standards Administration Institu
5、tion of Gas Engineers Institution of Mechanical Engineers Society of British Gas Industries Water Services Association of England and Wales Amendments issued since publication Amd. No. Date Comments 8879 December 1995 Indicated by a sideline in the marginBS7405:1991 BSI 03-2000 i Contents Page Commi
6、ttees responsible Inside front cover Foreword vi Section 1. General 1.0 Introduction 1 1.1 Scope 1 1.2 Definitions 1 1.3 Symbols 3 1.4 Flowmeter classification 4 1.5 Proprietary names 6 Section 2. General selection procedure 2.0 Introduction 7 2.1 Basic meter selection 7 2.2 Performance consideratio
7、ns 12 2.3 Fluid property considerations 16 2.4 Installation considerations 19 2.5 Environmental considerations 23 2.6 Economic considerations 23 2.7 Examples of flowmeter selection 25 Section 3. Flow measurement techniques 3.0 Introduction 31 3.1 Group 1 meters: orifices, venturis and nozzles 31 3.2
8、 Group 2 meters: other differential pressure types 41 3.3 Group 3 meters: positive displacement types 56 3.4 Group 4 meters: rotary turbine type meters 69 3.5 Group 5 meters: fluid oscillatory types 81 3.6 Group 6 meters: electromagnetic types 88 3.7 Group 7 meters: ultrasonic types 96 3.8 Group 8 m
9、eters: direct and indirect mass types 104 3.9 Group 9 meters: thermal types 110 3.10 Group 10 meters: Miscellaneous types 114 Section 4. Flowmeter applications 4.0 Introduction 124 4.1 Group 1 meter applications: orifices, venturis and nozzles 124 4.2 Group 2 meter applications: other differential p
10、ressure types 134 4.3 Group 3 meter applications: positive displacement (PD) types 147 4.4 Group 4 meter applications: rotary turbine types 154 4.5 Group 5 meter applications: fluid oscillatory types 164 4.6 Group 6 meter applications: electromagnetic types 173 4.7 Group 7 meter applications: ultras
11、onic types 179 4.8 Group 8 meter applications: direct and indirect mass types 184 4.9 Group 9 meter applications: thermal types 189 4.10 Group 10 meter applications: miscellaneous types 195 Section 5. Auxiliary instrumentation 5.0 Introduction 199 5.1 Pressure and differential pressure measurement 1
12、99 5.2 Temperature measurement 210 5.3 Density measurement 217 5.4 Humidity measurement 226BS7405:1991 ii BSI 03-2000 Page 5.5 Ancillary electrical equipment 231 Section 6. Flowmeter calibration 6.0 Introduction 239 6.1 Calibration conditions 239 6.2 Factors to be considered in calibration 239 6.3 C
13、alibration techniques for flowmeters 240 6.4 Traceability 240 Appendix A Bibliography 241 Appendix B Estimation of flow measurement uncertainty 243 Index 246 Figure 2.1 Example of the effect of metering error on two methods of specifying flowmeter uncertainty 13 Figure 2.2 Flowmeter linearity 13 Fig
14、ure 2.3 Typical performance distribution of flowmeter groups 15 Figure 2.4 Size distribution of flowmeter groups 22 Figure 2.5 Flowmeter purchase price comparison (liquids) 27 Figure 3.1.1 Pressure profile and flow pattern through an orifice meter 32 Figure 3.1.2 Typical orifice plate installation 3
15、4 Figure 3.1.3 Corner, flange and D and tap orifice designs 36 Figure 3.1.4 Classical venturi meter design 37 Figure 3.1.5 ISA 1932 nozzle design 39 Figure 3.1.6 Long radius flow nozzles 40 Figure 3.1.7 Venturi nozzle 41 Figure 3.2.1 Dall tube 42 Figure 3.2.2 Lo-Loss flow tube 42 Figure 3.2.3 Epiflo
16、 meter 43 Figure 3.2.4 One design of Gentile tube 43 Figure 3.2.5 Wedge meter 44 Figure 3.2.6 Orifice plates 45 Figure 3.2.7 Simplified arrangement of the Rotary Shunt meter 46 Figure 3.2.8 Variable area flowmeter 47 Figure 3.2.9 Variable area differential pressure meter 49 Figure 3.2.10 NPL standar
17、d pitot-static tube 50 Figure 3.2.11 Insertion type flowmeters 52 Figure 3.2.12 Borda inlet 53 Figure 3.2.13 Basic sonic flow nozzle 54 Figure 3.2.14 Elbow meter 56 Figure 3.2.15 Target meter 57 Figure 3.3.1 Basic positive displacement meter performance for a 25mm rotary piston type 58 Figure 3.3.2
18、Typical cruciform reciprocating piston meter 60 Figure 3.3.3 Sliding vane displacement meter 61 Figure 3.3.4 Helical displacement meters 62 Figure 3.3.5 Rotary piston meter 63 Figure 3.3.6 Nutating disc meter 64 Figure 3.3.7 Metering pump 65 Figure 3.3.8 Operation of a gas diaphragm meter 66 Figure
19、3.3.9 Rotary CVM gas meter 67 D 2 -BS7405:1991 BSI 03-2000 iii Page Figure 3.3.10 Wet gas displacement meter 68 Figure 3.4.1 Basic elements of turbine flowmeter 70 Figure 3.4.2 Turbine flowmeter characteristics 72 Figure 3.4.3 Typical helix type or Woltmann meter 74 Figure 3.4.4 Jet (or vane) type m
20、echanical meter 75 Figure 3.4.5 Performance characteristics for vane type meter 76 Figure 3.4.6 Propeller type meter 77 Figure 3.4.7 Pelton wheel inferential flowmeter 78 Figure 3.4.8 Twin rotor turbine flowmeter 79 Figure 3.4.9 Bearingless turbine type meter 80 Figure 3.4.10 Design and operation of
21、 RF type pick-off 81 Figure 3.5.1 Phenomenon of vortex shedding 82 Figure 3.5.2 Plan view of typical bluff body shapes 85 Figure 3.5.3 Vortex sensing designs 86 Figure 3.5.4 Fluidic oscillating flowmeter 87 Figure 3.5.5 Swirlmeter 88 Figure 3.6.1 Principle of an electromagnetic flowmeter 89 Figure 3
22、.6.2 Exploded view of the primary device of an electromagnetic flowmeter 90 Figure 3.6.3 Principle of a pulsed d.c. (bipolar) system 92 Figure 3.6.4 Modern compact electromagnetic flowmeter 94 Figure 3.6.5 Electromagnetic velocity probe 95 Figure 3.7.1 Principle of transit time ultrasonic flowmeter
23、97 Figure 3.7.2 Ultrasonic flowmeter designs 99 Figure 3.7.3 Ultrasonic leading edge technique 100 Figure 3.7.4 Ultrasonic sing-around technique 101 Figure 3.7.5 Time-of-flight design variations 102 Figure 3.7.6 Doppler meter design details 104 Figure 3.8.1 Driven angular momentum mass flowmeter 106
24、 Figure 3.8.2 Schematic of a twin turbine mass meter 106 Figure 3.8.3 Modern industrial Coriolis mass meter 108 Figure 3.8.4 Coriolis mass meter with straight tube sensing section 108 Figure 3.8.5 Parallel venturi mass meter 109 Figure 3.8.6 Orifice based differential pressure mass meter 109 Figure
25、3.9.1 Schematic arrangement of a thermal anemometer 111 Figure 3.9.2 Typical hot wire probe head 112 Figure 3.9.3 Designs of hot film anemometers 113 Figure 3.9.4 Sensing tip of typical flare gas thermal meter 113 Figure 3.9.5 Thomas thermal flowmeter 114 Figure 3.9.6 Thermal profile meter 115 Figur
26、e 3.10.1 Cross correlation flowmeter 118 Figure 3.10.2 Tracer transit time method 119 Figure 3.10.3 Output curves for dilution tracer techniques 119 Figure 3.10.4 Schematic of a nuclear magnetic resonance meter 121 Figure 3.10.5 Laser Doppler anemometry 122 Figure 3.10.6 NEL gas ionization meter 123
27、 Figure 4.1.1 Comparison of head loss for different DP devices 127 Figure 4.1.2 Tube bundle flow straightener 129BS7405:1991 iv BSI 03-2000 Page Figure 4.1.3 Square root error effect from pulsating flow through a DP meter 130 Figure 4.1.4 Total error at low pulsation amplitude (frequency range 50Hz
28、to 500Hz) 131 Figure 4.1.5 Examples of methods of reduction of pulsation effects in gas flow 132 Figure 4.1.6 Effect of swirl on orifice flowmeters 133 Figure 4.2.1 Orientation of segmental orifice plates 137 Figure 4.2.2 Typical discharge coefficient curves for eccentric orifices showing effect of
29、tap position 139 Figure 4.2.3 Influence of fluid properties on wedge meter orientation 142 Figure 4.2.4 Installation guidelines for multi-port averaging pitots 144 Figure 4.2.5 Removable installation of a multi-port averaging pitot 146 Figure 4.3.1 Effect of viscosity on the pressure drop of an oval
30、 gear meter 151 Figure 4.3.2 Common installation pitfalls for positive displacement meters 153 Figure 4.3.3 Typical high performance metering installation 154 Figure 4.3.4 Complete pipeline metering system using displacement meters 155 Figure 4.4.1 Pressure drop along length of a turbine meter 157 F
31、igure 4.4.2 Effect of viscosity on turbine meter performance 159 Figure 4.4.3 Effect of gas pressure (density) on turbine meter performance 160 Figure 4.4.4 Effect of two-phase flow on turbine meter performance 162 Figure 4.4.5 Effect of swirl on turbine meters 163 Figure 4.4.6 Response of turbine m
32、eter to step changes in flow rate 164 Figure 4.5.1 Typical sizing charts for vortex meter 166 Figure 4.5.2 Recommended vortex meter installation 170 Figure 4.5.3 Pipe connection details for vortex meter installation 171 Figure 4.5.4 Suggested circuit for voltage to current conversion for vortex flow
33、meter 172 Figure 4.6.1 Typical a.c. electromagnetic flowmeter performance curve 174 Figure 4.6.2 Typical pulsed d.c. electromagnetic flowmeter performance curve 176 Figure 4.6.3 Electromagnetic flowmeter installation pitfalls 177 Figure 4.6.4 Installation details for electromagnetic flowmeter instal
34、lations 178 Figure 4.6.5 An example of a manufacturers electromagnetic meter sizing chart 179 Figure 4.7.1 Typical transit time ultrasonic flowmeter spool piece 181 Figure 4.7.2 Clamp-on transit time ultrasonic flowmeter 181 Figure 4.7.3 Part of sizing table for transit time ultrasonic flowmeters 18
35、3 Figure 4.8.1 Typical pressure drop characteristics for Coriolis mass flowmeters 187BS7405:1991 BSI 03-2000 v Page Figure 4.8.2 Typical installation arrangements for indirect and direct systems 190 Figure 4.9.1 Output characteristic of a thermal anemometer 191 Figure 4.9.2 Typical output from a the
36、rmal profile meter 193 Figure 5.1.1 Simple Bourdon gauge 201 Figure 5.1.2 Capacitance pressure cell 205 Figure 5.1.3 Semi-conductor strain gauge pressure gauge 206 Figure 5.1.4 Example of pressure transducer installation for gases 208 Figure 5.1.5 Typical pressure transducer installation for fluids
37、209 Figure 5.2.1 Typical thermocouple construction 211 Figure 5.2.2 Cold junction compensation 212 Figure 5.2.3 Thermocouple characteristics 213 Figure 5.2.4 Construction of a platinum resistance thermometer (PRT) 215 Figure 5.2.5 Construction of a thermistor probe 216 Figure 5.3.1 Process weighing-
38、based densitometer 219 Figure 5.3.2 Pyknometer bottle 219 Figure 5.3.3 Density determination 221 Figure 5.3.4 Operating principle of vibrating element densitometer 222 Figure 5.3.5 Typical liquid densitometer 223 Figure 5.3.6 Typical specific gravity transducer for gases 224 Figure 5.3.7 Schematic p
39、ressure, temperature and density compensated metering system 227 Figure 5.5.1 Range of instruments for use with flowmeters 233 Figure 5.5.2 Process chart recorder 235 Figure 5.5.3 Orifice metering system 235 Figure 5.5.4 Computer based proving system 236 Figure 5.5.5 Zener barrier 238 Figure B.1 Ter
40、minology for measurement uncertainty 245 Table 1.1 Symbols 3 Table 1.2 Flowmeter classification 4 Table 1.3 Group designations of flowmeters 5 Table 2.1 Broad areas of application 8 Table 2.2 Selection procedure variables 9 Table 2.3 Performance factors in meter selection 11 Table 2.4 Selection by f
41、luid property constraints 17 Table 2.5 Selection by installation constraints 20 Table 2.6 Selection by environmental constraints 24 Table 2.7 Selection by economic factors 26 Table 3.7.1 Example multi-beam ultrasonic meter weighting factors 102 Table 4.2.1 Typical upstream pipe lengths for multi-por
42、t averaging pitots 143 Table 4.3.1 Correction factors for a sliding vane meter for different fluids 150 Table 4.4.1 Recommended filter characteristics for group4meters 161 Table 4.5.1 Typical low flow limits for vortex and fluidic meters 167BS7405:1991 vi BSI 03-2000 Page Table 4.5.2 Recommended min
43、imum upstream lengths for vortex flowmeter installation 169 Table 4.6.1 Electromagnetic flowmeter liner types 174 Table 5.1.1 Relative pressure and differential pressure transducer performance characteristics 203 Table 5.1.2 Typical pressure and differential pressure transducer application character
44、istics 204 Table 5.2.1 Thermocouple types 211 Table 5.2.2 Characteristics of liquid-in-glass thermometers 214 Table 5.4.1 Operating principles of the most common hygrometers 228 Table 5.5.1 The two main systems of gas classification 237 Table 5.5.2 Temperature classification system universally used
45、237 Table 5.5.3 The two main systems of area classification 238 Publication(s) referred to 250BS7405:1991 BSI 03-2000 vii Foreword This British Standard has been prepared under the direction of the Industrial-process Measurement and Control Standards Policy Committee. Grateful acknowledgement is mad
46、e of the wide range of useful comments received on circulation of the Draft for Public Comment, many of which were taken into account in the further development of the draft. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are res
47、ponsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi toviii, pages1to250, an inside back cover and a back cover. This standard has be
48、en updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.viii blankBS7405:1991 BSI 03-2000 1 Section 1. General 1.0 Introduction Flow measurement is one of the most important of all process measurements. Millions of pounds worth of fluids are bought and sold each day, with the value being determined by flow measurement. The control of chemical and other process plants also relies heavily on the performance of a wide range of different types of flowm
