1、I STDmBSI BS IS0 7278-3-ENGL 3998 3624669 0735953 2T3 BRITISH STANDARD Liquid hydrocarbons - Dynamic measurement - Proving systems for volumetric meters - Part 3: Pulse interpolation techniques ICs 75.180.30 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BS IS0 72 78-3: 1998
2、IS0 727831998 STD-BSI BS IS0 7278-3-ENGL 1998 M 1624669 0715954 138 M BS Is0 7278-3:1998 AmdNo. National foreword Date nxt affected This British standard reproduces verbatim IS0 72783: 1998 and implements it as the K national standard. It supersedes BS 6866:Part 3: 1987 which is withdrawn. The UK pa
3、rticipation in its preparation was entrusted by Technid Commit - monitor related international and European developments and promulgate them in the UK. A list of organizations represented on this subcommitee can be obtained on request to its secretary. Cross-references The British Standards which im
4、plement international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “Inkrmtional Standards Correspondence Index“, or by using the “Find“ facility of the BSI Standards Electsonic Catalogue. A British Standard does not purp
5、ort to include all the necessary provisions of a contract. Users of British Standads are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from iegai obligations. This British Standard, having been prepared under the direction of the Sec
6、tor Board for Materials and Chemicals, was published under the authority of the Standards Board and comes inta effect on 15 August 1998 O BSI 1998 ISBN O 680 30209 1 STD-ES1 ES IS0 7278-3-ENGL 1998 1624669 0735955 074 BS IS0 7278-3:1998 INTERNATIONAL IS0 STANDARD 7278-3 Second edition 1998-02-1 5 Li
7、quid hydrocarbons - Dynamic measurement - Proving systems for volumetric meters - Part 3: Pulse interpolation techniques Hydrocarbures liquides - Mesurage dynamique - Systemes dtalonnage pour compteurs volumtriques - Partie 3: Techniques dinterpolation des impulsions Reterence number IS0 7278-3:1998
8、(E) STD-BSI BS IS0 7278-3-ENGL 1998 W 1b24bb9 071595b TOO BS IS0 7278-31998 Contents Page 1 Scope 1 2 Normative reference . 3 Definitions . 4 Principles 4.2 Double-timing method . 4.3 Quadruple-timing method . 4.4 Phase-locked-loop method . 4.1 General . 5 Conditions of use 5.1 General . 5.2 Double-
9、timing method . 5.3 Quadruple-timing method . 5.4 Phase-locked-loop method . 6 Meter requirements . 7 Tests for pulse interpolation system . 7.1 General . 7.2 Test circuit 7.3 Test schedule . 7.4 Immunity from electrical noise 8 Test report and markings Annex A (normative) Measurement techniques for
10、 determining pulse intervals . Annex B (informative) Bibliography . 1 1 6 9 10 12 0.rciiptors: petroleum products. hydrocarbons. liquid flow. flow measurement. flowmeters. calibration . i * * m STD-BSI BS IS0 7278-3-ENGL 1998 1624669 0735957 947 BS IS0 7278-3:1998 Foreword IS0 (the International Org
11、anization for Standardization) is a worldwide federation of national standards bodies (IS0 member 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 establi
12、shed has the right to be represented on that committee. International organizations, governmental 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 standardizatio
13、n. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an Intemational Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard IS0 7278-3 was prepared by Technical Committee I
14、SOTTC 28, Petroleum products and lubricants, Subcommittee SC 2, Dynamic petroleum measurement. This second edition cancels and replaces the first edition (IS0 7278-3:1986), which has been technically revised, in particular with addition of annex A and annex B. IS0 7278 consists of the following part
15、s, under the general title Liquid hydrocarbons - Dynamic measurement - Proving systems for volumetric meters: - Part 7: General principles - Part 2: Pipe provers - Part 3: Pulse interpolation techniques - Part 4: Guide for operators of pipe provers - Part 5: Small volumekompact provers Annex A forms
16、 an integral part of this part of IS0 7278. Annex B is for information only. . 111 STDmBSI BS IS0 7278-3-ENGL 1998 D 1624bb9 0715958 883 BS IS0 7278-3:1998 Introduction The use of pipe provers to prove meters with pulsed outputs requires that a minimum number of pulses be collected during the provin
17、g period. The number of pulses which a meter can produce during a proving run is oten limited to significantly less than 10 O00 pulses. Therefore, in many applications some means of increasing the meters resolution has to be found. One way of overcoming this problem is to process the signal from the
18、 meter in such a way that the resolution of the meter is increased. This technique is known as pulse interpolation. This part of IS0 7278 applies primarily to pipe provers, but it is not intended to restrict in any way the future development of different methods of pulse interpolation to this and ot
19、her applications. iv * Ln k STD=BSI BS IS0 7278-3-ENGL 1998 W Bb24bb9 0735959 7BT BS IS0 7278-3:1998 Liquid hydrocarbons - Dynamic measurement - Proving systems for volumetric meters - Part 3: Pu Ise in te rpolat ion tech niques 1 Scope This part of IS0 7278 gives guidance on the procedures and cond
20、itions of use to be observed if pulse interpolation is used in conjunction with a pipe or small volume prover and a turbine or displacement meter to improve the discrimination of proving. This part of IS0 7278 describes the three methods of pulse interpolation most commonly used and their conditions
21、 of use. It also describes the equipment and test procedures for checking that the pulse interpolation system is operating satisfactorily and it describes some methods of measuring the irregularity of pulse spacing for a meter. 2 Normative reference The following standard contains provisions which,
22、through reference in this text, constitute provisions of this part of IS0 7278. At the time of publication, the edition indicated was valid. All standards are subject to revision, and parties to agreements based on this part of IS0 7278 are encouraged to investigate the possibility of applying the m
23、ost recent edition of the standard indicated below. Members of IEC and IS0 maintain registers of currently valid International Standards. IS0 6551:1982, Petroleum liquids and gases - Fidelity and security of dynamic measurement - Cabled transmission of electric and/or electronic pulse data. 3 Defini
24、tions For the purposes of this pari of IS0 7278, the following definitions apply. 3.1 clock: Device for generating a stable frequency, the period of which is used as a standard reference for time measurements. 3.2 detector signal: Contact closure or voltage change that starts or stops the indicating
25、 device. 3.3 intra-rotational linearity: Quantitative measure of the degree of regularity of spacing between the pulses, produced by a rotating meter at constant flowrate, generally expressed as the standard deviation of pulse spacing about the mean pulse spacing. This measure will include cyclic an
26、d non-cyclic measurements introduced by the meter mechanism. The pulse spacing is the time between the leading or lagging edges of consecutive pulses. NOTE - Intra-rotational linearity is the regularity measurement which repeats in a periodic or cyclic manner attributed to the rotation of the meter.
27、 - 3.4 leadingllagging edge: Rising or falling voltage of a pulse used to trigger or gate a counter. 3.5 phase detector: Electronic circuit which detects a phase difference between two pulse frequencies. 1 STD-ES1 BS IS0 7278-3-ENGL 1998 1624669 0715960 431 H BS IS0 7278-31998 3.6 ramp generator: El
28、ectronic circuit whose output voltage varies linearly with time. NOTE - Non-linear ramp generators are not used. 3.7 repeatability (of measurement instrument): Closeness of the agreement between the results measurements of the same measurand carried out under the same conditions of measurement VIM.
29、of successive NOTE - The defined conditions of use are usually as follows: - repetition over a short period of time; - use at the same location under constant ambient conditions; - reduction to a minimum of the variations due to the observer. 3.8 resolution: Quantitative expression of the ability of
30、 an indicating device to distinguish meaningfully between closely adjacent values of the quantity indicated VIM. 3.9 rotating meter: Meter, the measuring element of which has one or more rotating parts driven by the flowing fluid (e.g. turbine meters and displacement meters). NOTE- For the purposes
31、of this part of IS0 7278, the output from the meter should be in the form of electrical pulses, the mean frequency of which is a function of the flowrate. 4 Principles 4.1 General The following points are applicable when using any of the three techniques of pulse interpolation described in this part
32、 of IS0 7278. a) The use of pulse interpolation is based on the assumption that there is no significant variation in the frequency of the pulses. Any variations in frequency caused by flowrate (see Sic), or especially by intra-rotational non- linearity (see clause 6) will degrade the accuracy. b) Th
33、e interpolated number of pulses n as described in 4.2, 4.3 and 4.4, will not generally be a whole number. Muitiple pulses from a flowmeter may be generated during a revolution of the meter, or to reduce intra-rotational non-linearity a single pulse per revolution may be used. 4.2 Double-timing metho
34、d See figure 1. The principle of operation of this method is shown in figure 1. It consists of collecting, in a counter, the total number of complete meter pulses, n, generated during a proving run, and measuring two time-intervals, T1 and T2. a) TI is the time-interval between the first meter pulse
35、 following the first detector signal and the first meter pulse following the last detector signal; b) T2 is the time-interval between the first and last detector signals. The interpolated number of pulses is then given by 2 STD.BSI BS IS0 7278-3-ENGL 1998 - 1624669 0715961 378 m BS IS0 7278-3:1998 -
36、 Detector signal Detector signal J2 -i Interpolated number of pulses, n = n 2 or n = n - 2 T10) Ti() Figure 1 - Double-timing method 4.3 Quadruple-timing method See figure 2. The principle of operation of this method is shown in figure 2. It consists of collecting, in a counter, the total integral n
37、umber of pulses, n, generated during a proving run and measuring four time-intervals, tl to 4. a) b) ti is the time-interval between the first detector signal and the first meter pulse following that signal; t2 is the time-interval between the last meter pulse before the first detector signal and th
38、e first meter pulse after it; c) d) t3 is the time-interval between the second detector signal and the first meter pulse following that signal; 4 is the time-interval between the last meter pulse before the second detector signal and the first meter pulse after it. The number of complete pulses, n,
39、in the main pulse count is counted in the normal way by a counter gated by the detector signals. The interpolated number of pulses, n, between the detector signals is then - Meter pulses - o Interpolated number of pulses, n = n + - 4 - - t3 t2 t4 Figure 2 - Quadruple-timing method 3 - STD-BSI BS IS0
40、 7278-3-ENGL 1998 m Lb24bb9 03359b2 204 m BS IS0 7278-3:1998 Meter pulses Input 1 Phase comparator Input 2 4.4 Phase-locked-loop method Meter puises Voltage- =R - filter - controlled oscillator See figure 3. The principle of operation of this method is shown in figure 3. The pulses from the meter ar
41、e introduced to input 1 of the phase comparator and the output signal is passed to the voltage controlled oscillator (VCO). This device generates pulses with a higher frequency proportional to its input voltage. This frequency is chosen to be higher than the meter frequency. The output signal of the
42、 VCO is also fed back, through a frequency divider, to input 2 of the phase comparator. The frequency of the multiplied pulses is reduced by the divisor, R. The output voltage of the phase comparator is proportional to the difference in phase or frequency between its two inputs, so that the output f
43、requency of the VCO is continually being servo-controlled to ensure that the frequency and phase of the two inputs are identical. The selection of frequency divisor, , thus determines the pulse interpolation divisor. The interpolated number of pulses collected during the proving run is normally expr
44、essed as n“ n= - R where n“ is the number of multiplied pulses collected from the multiphase output; R is the selected divisor (or multiplication factor). Detector signal Start Detector signal stop n* pulses of the higher frequency n* Interpolated number of pulses, n = - R Figure 3 - Phase-locked-lo
45、op method 4 - STD*BSI ES IS0 7278-3-ENGL 1998 W Lb24669 0735963 140 BS IS0 7278-3:1998 To achieve precise control, it is necessary to filter the output of the phase comparator to avoid sudden VCO changes. This filter, normally of the simple RC type, has the property of momentarily retaining the volt
46、age required by the VCO to keep generating R times the meter frequency between each phase comparison. Selection of the filters time constant should be chosen to provide stability but not mask changes in input pulse frequency due to flowrate fluctuation. 5 Conditions of use 5.1 General The following
47、conditions shall apply generally to all the pulse interpolation methods described in this part of IS0 7278. a) Resolution The resolution of the indication device attached to the system shall in all instances be better than 1 in 10 000. b) Number of significant digits for n As stated in 4.1 b), the n
48、umber n will not necessarily be a whole number. For the timing methods which yield a fractional result, there will be a practical limit on the number of decimal places which are used for n. In practice the improvement by pulse interpolation is not unlimited, as n shall be rounded to five significant
49、 digits, not more and not less. c) Stability of flowrate The pulse interpolation methods are based on the assumption that the flow is stable during the period of the proving. To maintain the stability of the flow, the fluctuations in the flowrate during a pass of the prover displacer, shall be less than I 2 Oh of the mean flowrate. NOTES 1 The pulse interpolation equipment is tested under conditions of simulated flowrate variation (see 7.3) to show Satisfactory operation with such fluctuations. 2 The stability of the mete
