1、STD-BSI BS ISO/TR 127b5-ENGL 17790 Lb24bbY 075bb4U iI70 BRITISH STANDARD Measurement of fluid flow in closed conduits - Methods using transit-time ultrasonic flowmeters ICs 17.120.10 BS ISOLR 12 765: 1998 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGW LAW STD.8SI BS ISO/TR L27b5-E
2、NGL 1178 Lb24bb9 075bbliL 327 I been prepared under the Committee for Materiais and Chemicals, was published under the authority of the Standards Committee and comes into effect on 15 March 1999 direction of the Sector Amd. No. Date O BSI 03-1999 ISBN O 680 29384 X BS ISOm 12765:1998 Text affected N
3、ational foreword This British Standard reproduces verbatim ISOm 12765 1998 and implements it as the UK national standard. The UK participation in its preparation was entrusted by Technical Coinmittee CPIBO, Measurement of fluid flow in closed conduits, to Subcommittee CPI/30/5, Velocity based method
4、s, which has the responsibility to: - aid enquirers to understand the text; - present to the responsible intemationaVEuropean committee any enquiries on the interpretation, or propods for change, and keep the UK interests informed; - monitor related international and European developments and promul
5、gate them in the UK A list of organizations represented on this subcommittee can be obtained on request to its secretary. Cross-references The British Standards which implement international or European publications referred to in this document may be found in the BSI Standards Catalogue under the s
6、ection entitled “Inkrnational Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct applicatio
7、n. 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, the ISOAX title page, pages ii and iii, a blank page, pages 1 to 43 and a back cover. BS ISO/TR 12765:1998 TECHNICAL REPORT
8、ISOITR 12765 First edition 1998-12-1 5 Measurement of fluid flow in closed conduits - Methods using transit-time ultrasonic flowmeters Mesure de dbit des fluides dans /es conduites fermes -Mthodes utilisant des dbitmtres A ultrasons a temps de transit Reference number ISOTTR 127651 998(E) BS ISOPTR
9、12765:1998 Contents Page 1 scope 1 2 Normative references 1 3 Definitions 1 4 Symbols and subscripts . 8 5 General principles of measurements . 9 5.1 Generation of ultrasonic signals . 9 5.2 Transit-time method . 11 5.3 Calculation of volume flowrate % . 14 6 Types of design 15 6.1 Ultrasonic transd
10、ucer . 15 6.2 Control unit 20 7 Uncertainty of measurement 20 7.1 Calculation procedure 20 7.2 Influence factors . 22 8 Calibration 24 8.1 Dry calibration . 24 8.2 Flow calibration . 25 Annex A (informative) Calculation of volume flowrate by transit-time measurement using pulse techniques 26 Annex B
11、 (informative) Recommendations for use and installation . 35 Annex C (informative) Information to be supplied by the manufacturer . 40 Bibliography 43 BS ISO/TR 12765:1998 Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 me
12、mber bodies). The work of preparing International Standards is normally carried out through IS0 technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governme
13、ntal and non-governmental, in liaison with ISO, also take part in the work. IS0 collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. The main task of technical committees is to prepare International Standards, but in except
14、ional circumstances a technical committee may propose the publication of a Technical Report of one of the following types: - type 1, when the required support cannot be obtained for the publication of an International Standard, despite repeated efforts; - type 2, when the subject is still under tech
15、nical development or where for any other reason there is the future but not immediate possibility of an agreement on an International Standard; - type 3, when a technical committee has collected data of a different kind from that which is normally published as an International Standard (“state of th
16、e art”, for example). Technical Reports of types 1 and 2 are subject to review within three years of publication, to decide whether they can be transformed into International Standards. Technical Reports of type 3 do not necessarily have to be reviewed until data they provide are considered to be no
17、 longer valid or useful. ISOTTR 12765, which is a Technical Report of type 2, was prepared by Technical Committee ISO/TC 30, Measurement of fluid flow in closed conduits. This document is being isssued in the type 2 Technical Report series of publications (according to subclause G.4.2.2 of part 1 of
18、 the ISOAEG Directives, 1992) as a “prospective standard for a provisional application” in the field of ultrasonic flowmeters because there is an urgent need for guidance on how standards in this field should be used to meet an identified need. This document is not to be regarded as an “Internationa
19、l Standard. It is proposed for provisional application so that information and experience of its use in practice may be gathered. Comments on the content of this document should be sent to the IS0 Central Secretariat. A review of this type 2 Technical Report will be carried out not later than three
20、years after its publication with the options of: extension for another three years; conversion into an International Standard; or withdrawal. Annexes A, B and C of this Technical Report are for information only. iii STD-BSI BS ISO/TR 12705-ENGL L99 Lb24bb7 75bL45 172 m BS ISO/TR 12765:1998 Measureme
21、nt of fluid flow in closed conduits - Methods using transit-time ultrasonic flowmeters 1 Scope This Technical Report gives guidance on the principles and main design features of ultrasonic flowmeters based on the measurement of the difference in transit time for volume flowrate measurement of fluids
22、. It covers their operation, performance and calibration. It primarily covers wetted transducers but briefly refers to clamp-on transducer arrangements. Annex A of this Technical Report shows the calculation of volume flowrate by transit-time measurement using pulse techniques. Annex B covers the re
23、commendations for use and installation. Annex C gives a list of information to be supplied by the manufacturers. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this Technical Report. At the time of publication, the ed
24、itions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of current
25、ly valid International Standards. IS0 4006:1991, Measurement of fluid flow in closed conduits - Vocabulary and symbols. IS0 41 85:1980, Measurement of liquid flow in closed conduits - Weighting method. IS0 8316:1987, Measurement of liquid flow in closed conduits - Method by collection of the liquid
26、in a volumetric tank. IS0 9300:1990, Measurement of gas flow by means of critical flow Venture nozzles. is0 9951 :1993, Measurement of gas flow in closed conduits - Turbine meters. International Vocabulary of Basic and General Terms in Metrology (VIM), BIPM, IEC, IFCC, ISO, IUPAC, IUPAP, OIML, 1993.
27、 3 Definitions For the purposes of this Technical Report, the definitions given in the International Vocabulary of Basic and General Terms in Metrology (VIM), IS0 4006 and the following definitions apply. 1 STD*BSI BS ISO/TR L27L5-ENGL 1978 U Lb24bb7 075bb4b 709 II BS ISO/TR 12765:1998 3.1 transit-t
28、ime difference method time-of-flight method method of flowrate measurement in which the average fluid velocity along the acoustic path is determined from the transit-time difference of two ultrasonic signals, one travelling upstream and one downstream, over the same distance in the flowing fluid 3.2
29、 leading-edge method method of flowrate measurement in which the transit times of ultrasonic pulses are measured based on triggering at a predetermined amplitude level of the received signal See Figure 1. Key 1 Trigger point at leading edge Figure 1 - Principle of transit-time measurement using lead
30、ing-edge method 3.3 pulse-repetition frequency method sing-around method frequency-difference method method of flowrate measurement used in ultrasonic flowmeters whereby two independent streams of pulses are transmitted in opposite directions, each pulse being emitted immediately after the detection
31、 of the preceding pulse in the stream, and the difference between the pulse-repetition frequencies in the two directions is measured NOTE The difference between the pulse-repetition frequencies in the two directions is a function of the fluid velocity. 3.4 phase control method lambda-locked-loop met
32、hod method of flowrate measurement in which a measure of the average fluid velocity along the acoustic path V is derived from the difference in frequency of sound with the same wavelength travelling in opposite directions through the flowing fluid 3.5 zero-crossing method method of flowrate measurem
33、ent in which transit times of ultrasonic pulses are measured using the first (or another predetermined) “zero-crossing“ of the received signal following the first half alternance See Figure 2. _ STD-BSI BS ISO/TR 127b5-ENGL 1778 1b2L(bb9 075bb47 45 BS ISOPTR 12765:1998 Key 1 Trigger point at zero cr
34、ossing Figure 2 - Principle of transit-time measurement using zero-crossing method 3.6 multi-path method method of flowrate measurement in which the average fluid velocity over a number of different paths is determined 3.7 simultaneous pulse method method of flow measurement by which the transit tim
35、es and transit-time difference are determined from signals which are transmitted simultaneously upstream and downstream over the same acoustic path 3.8 phase shift method method of flow measurement in which the average fluid velocity along the acoustic path V is determined from the phase shift of ul
36、trasonic signals in a fluid flow 3.9 ultrasonic flowmeter USM flowmeter which generates ultrasonic signals and receives them again after they have been influenced by the flow in such a way that the observed result can be used as a measure of the flowrate NOTE An ultrasonic flowmeter normally consist
37、s of the ultrasonic transducers and equipment which evaluates the flowrate measurement from the emitted and received ultrasonic signals and converts these signals to a standard output signal proportional to the flowrate , 3.1 O flowrate integrator device for volume measurement by time-integration of
38、 volume flowrate 3.1 1 ultrasonic transducer element that converts acoustic energy into electrical signals and/or vice versa NOTE Ultrasonic transducers used in transit-time flowmeters usually work as both transmitter and receiver. 3.12 clamp-on arrangement arrangement by which the transducers are a
39、ttached to the outside wall of the conduit in which the flowrate is to be measured 3 STD.BSI BS ISO/TR L27b5-ENGL 1998 Lb24bb9 1175bb48 781 BS ISOBR 12765:1998 3.1 3 meter tube specially fabricated section of conduit containing the ultrasonic transducers and conforming in all respects to the specifi
40、cation of the standard 3.14 measurement section section of conduit consisting of the meter tube, the inlet section and the outlet section 3.15 acoustic path actual path of the ultrasonic signal between both transducers 3.16 path length length of acoustic path, in fluid at rest, from the faces of bot
41、h transducers LP See Figure 3 a) and b). 3.17 interrogation length L length of that part of the acoustic path, in fluid at rest, inside the conduit See Figure 3 a) and b). 3.18 interrogation distance d projection of the interrogation length on the line parallel to the axis of the conduit or of the f
42、low See Figure 3 a) and b). 3.1 9 inclination angle o angle between the axes of the ultrasonic transducers and a line parallel to the axis of the conduit See Figure 3 a). 3.20 phase angle phase position of an oscillation 3.21 propagation velocity L velocity of acoustic signals relative to an observe
43、r at rest 3.22 velocity of sound CO velocity of acoustic signals in the fluid at rest 3.23 average fluid velocity along the acoustic path fluid velocity in the plane which is formed by the acoustic path and the direction of flow - V 4 BS ISO/TR 12765:1998 3.24 mean axial fluid velocity VA ratio of t
44、he volume flowrate (4“) the integral over a cross-section of the meter tube of the axial components of the local fluid velocities (v) to the area of the measurement cross-section (A) - 3.25 kh velocity distribution correction factor ratio of the mean axial fluid velocity TA in the meter run to the a
45、verage axial flow velocity V along the acoustic path 3.26 ultrasonic pulse signal generated by finite-duration electrical excitation of an ultrasonic transducer 3.27 continuous-wave ultrasound signal generated by continuous electrical excitation of an ultrasonic transducer 3.28 t transit time time n
46、eeded by an ultrasonic pulse to traverse the acoustic path 3.29 transit-time difference At difference between the transit times of the ultrasonic signals propagated upstream and downstream 5 STD.BS1 BS ISO/TR L27b5-ENGL 1778 E Lb24bb7 U75bb50 33T PI BS ISORR 12765:1998 2 Key 1 Receiver/emier 2 Emite
47、r/receiver a) Diagonal-direct beam meter Figure 3 - Arrangements of single-path beam meter (wetted transducers) 6 STD.BSI BS ISOITR L27b5-ENGL L798 Lb24bb 0756652 27b B BS ISO/TR 12765:1998 b) Diagonal-reflected indirect beam meter Figure 3 - Arrangements of single-path beam meter (wetted transducer
48、s) BS ISOflX 127651998 Quantity Cross-sectional area Propagation velocity in the flowing fluid Velocity of sound in fluid at rest Inside diameter of pipe Interrogation distance Frequency Relative uncertainty Absolute uncertainty Integer Velocity distribution correction factor Interrogation length Pa
49、th length Integer Integers (1, 2, 3, .) Volume flowrate Reynolds number (related to D) Transit time Transit-time difference Local velocity of the fluid Average fluid velocity along the acoustic path Mean axial fluid velocity Weight of measurement Phase angle Wavelength of an ultrasonic oscillation Inclination angle Cyclic frequency Density of the fluid 1) M = mass, L = length, T = time. 4 Symbols and subscripts Symbol Dimensions) Corresponding SI unit A L* rn2 C LT- m/S CO LT- m/S D L m d L m f T-1 S-1 E 2) e 3) 1 2) kh 2) L L m LP L m m 2) n
