1、Manual of PetroleumMeasurement StandardsChapter 4Proving SystemsSection 6Pulse InterpolationSECOND EDITION, MAY 1999ERRATA, APRIL 2007REAFFIRMED, OCTOBER 2013Manual of PetroleumMeasurement StandardsChapter 4Proving SystemsSection 6Pulse InterpolationMeasurement CoordinationSECOND EDITION, MAY 1999ER
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13、 publisher. Contact the Publisher, API Publishing Services, 1220 L Street, N.W., Washington, D.C. 20005.Copyright 1999 American Petroleum InstituteFOREWORDChapter 4 of the Manual of Petroleum Measurement Standards was prepared as a guide for the design, installation, calibration, and operation of me
14、ter proving systems commonly used by the majority of petroleum operators. The devices and practices covered in this chap-ter may not be applicable to all liquid hydrocarbons under all operating conditions. Other types of proving devices that are not covered in this chapter may be appropriate for use
15、 if agreed upon by the parties involved.The information contained in this edition of Chapter 4 supersedes the information con-tained in the previous edition (First Edition, May 1978), which is no longer in print. It also supersedes the information on proving systems contained in API Standard 1101, M
16、easure-ment of Petroleum Liquid Hydrocarbons by Positive Displacement Meter (First Edition, 1960); API Standard 2531, Mechanical Displacement Meter Provers; API Standard 2533, Metering Viscous Hydrocarbons; and API Standard 2534, Measurement of Liquid Hydro-carbons by Turbine-Meter Systems, which ar
17、e no longer in print. This publication is primarily intended for use in the United States and is related to the standards, specifications, and procedures of the National Bureau of Standards and Technol-ogy (NIST). When the information provided herein is used in other countries, the specifica-tions a
18、nd procedures of the appropriate national standards organizations may apply. Where appropriate, other test codes and procedures for checking pressure and electrical equipment may be used.For the purposes of business transactions, limits on error or measurement tolerance are usually set by law, regul
19、ation, or mutual agreement between contracting parties. This publi-cation is not intended to set tolerances for such purposes; it is intended only to describe methods by which acceptable approaches to any desired accuracy can be achieved.MPMS Chapter 4 now contains the following sections: Section 1,
20、 “Introduction”Section 2, “Conventional Pipe Provers”Section 3, “Small Volume Provers”Section 4, “Tank Provers”Section 5, “Master-Meter Provers”Section 6, “Pulse Interpolation”Section 7, “Field-Standard Test Measures”Section 8, “Operation of Proving Systems”Section 9, “Calibration of Provers”API pub
21、lications may be used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them; however, the Institute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclai
22、ms any liability or responsibility for loss or damage resulting from its use or for the violation of any federal, state, or municipal regulation with which this publication may conflict.Suggested revisions are invited and should be submitted to the general manager of the Upstream Segment, American P
23、etroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005.iiiCONTENTSPage0 INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24、. . . . . . . . . . . . . . . . . . .12 DEFINITIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14 DOUB
25、LE-CHRONOMETRY PULSE INTERPOLATION . . . . . . . . . . . . . . . . . . . . . .14.1 Conditions of Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24.2 Flowmeter Operating Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
26、. . . . .25 ELECTRONIC EQUIPMENT TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26 FUNCTIONAL OPERATIONS TEST REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . .27 CERTIFICATION TEST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
27、. . . . . . . . .28 MANUFACTURERS CERTIFICATION TESTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3APPENDIX A PULSE-INTERPOLATION CALCULATIONS . . . . . . . . . . . . . . . . . . . 5FiguresA-1 Double-Chronometry Timing Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28、. . . . .7A-2 Certification Test Equipment for Double-Chronometry Pulse Interpolation Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8v1Chapter 4Proving SystemsSection 6Pulse Interpolation0 IntroductionTo prove meters that have pulsed outputs, a minimu
29、m number of pulses must be collected during the proving period. The prover volume or the number of pulses that a flowmeter can produce per unit volume of throughput is often limited by design considerations. Under these conditions it is necessary to increase the readout discrimination of the flow-me
30、ter pulses to achieve an uncertainty of 0.01%. The electronic signal from a flowmeter can be treated so that interpolation between adjacent pulses can occur. The technique of improving the discrimination of a flowmeters output is known as pulse interpolation. Although pulse-inter-polation techniques
31、 were originally intended for use with small volume provers, they can also be applied to other prov-ing devices. The pulse-interpolation method known as double-chronometry, described in this chapter, is an established technique used in proving flowmeters. As other methods of pulse interpolation beco
32、me accepted industry practice, they should receive equal consideration, provided that they can meet the established verification tests and spec-ifications described in this publication. 1 ScopeThis chapter describes how the double-chronometry method of pulse interpolation, including system operating
33、 require-ments and equipment testing, is applied to meter proving. 2 Definitions2.1 detector signal: A contact closure change or other signal that starts or stops a prover counter or timer and defines the calibrated volume of the prover.2.2 double-chronometry: A pulse interpolation tech-nique used t
34、o increase the readout discrimination level of flowmeter pulses detected between prover detector signals. This is accomplished by resolving these pulses into a whole number of pulses plus a fractional part of a pulse using two high speed timers and associated gating logic, controlled by the detector
35、 signals and the flowmeter pulses. 2.3 flowmeter discrimination: A measure of the small-est increment of change in the pulses per unit volume of the volume being measured. 2.4 frequency: The number of repetitions, or cycles, of a periodic signal (for example, pulses, alternating voltage, or current)
36、 occurring in a 1-second time period. The number of repetitions, or cycles, that occur in a 1-second period is expressed in hertz. 2.5 meter pulse continuity: The deviation of the inter-pulse period of a flowmeter expressed as a percentage of a full pulse period.2.6 nonrotating meter: Any metering d
37、evice for which the meter pulse output is not derived from mechanical rota-tion as driven by the flowing stream. For example, vortex shedding, venturi tubes, orifice plates, sonic nozzles, and ultrasonic and electromagnetic flowmeters are metering devices for which the output is derived from some ch
38、aracter-istic other than rotation that is proportional to flow rate.2.7 pulse period: The reciprocal of pulse frequency, i.e., a pulse frequency of 2 hertz, is equal to a pulse period of 1/2seconds.2.8 pulse generator: An electronic device that can be programmed to output voltage pulses of a precise
39、 frequency or time period. 2.9 pulse interpolation: Any of the various techniques by which the whole number of meter pulses is counted between two events (such as detector switch closures); any remaining fraction of a pulse between the two events is calcu-lated.2.10 rotating meter: Any metering devi
40、ce for which the meter pulse output is derived from mechanical rotation as driven by the flowing stream. For example, turbine and posi-tive displacement meters are those metering devices for which the output is derived from the continuous angular dis-placement of a flow-driven member. 2.11 signal-to
41、-noise ratio: The ratio of the magnitude of the electrical signal to that of the electrical noise.3 ReferencesThe current editions of the following standards are cited in this chapter: API MPMS Chapter 4, Proving Systems Section 3, “Small Vol-ume Provers” Chapter 5, Metering Section 4, “Instrumentat
42、ion and Aux-iliary Equipment for Liquid Hydrocarbon Metering Systems”, Section 5, “Security and Fidelity of Pulse Data” 4 Double-Chronometry Pulse Interpolation Double-chronometry pulse interpolation requires counting the total integer (whole) number of flowmeter pulses, Nm, 2 MPMS CHAPTER 4PROVING
43、SYSTEMSgenerated during the proving run and measuring the time intervals, T1and T2. T1is the time interval between the first flowmeter pulse after the first detector signal and the first flowmeter pulse after the last detector signal. T2is the time interval between the first and last detector signal
44、s. The pulse counters, or timers, are started and stopped by the signals from the prover detector or detectors. The time intervals T1, corresponding to Nmpulses, and T2, corresponding to the interpolated number of pulses (N1), are measured by an accu-rate clock. The interpolated pulse count is given
45、 as follows: N1= Nm(T2/T1) The use of double-chronometry in meter proving requires that the discrimination of the time intervals T1 and T2be bet-ter than 0.01%. The time periods T1and T2shall therefore be at least 20,000 times greater than the reference period Tcof the clock that is used to measure
46、the time intervals. The clock frequency Fc must be high enough to ensure that both the T1and T2timers accumulate at least 20,000 clock pulses during the prove operation. This is not difficult to achieve, as current electronics technology used for pulse interpolation typically uses clock frequencies
47、in the megahertz range. 4.1 CONDITIONS OF USEThe conditions described in 4.1.1 through 4.1.3 apply to double-chronometry pulse interpolation as described in this chapter.4.1.1 The interpolated number of pulses, N1, will not be a whole number. N1is therefore rounded off as described in MPMS Chapter 1
48、2.2, Part 3. 4.1.2 Pulse-interpolation methods are based on the assumptions that actual flow rate does not change substan-tially during the period between successive meter pulses, and each pulse represents the same volume. To maintain the validity of these assumptions, short period fluctuations in t
49、he flow rate during the proving operation shall be minimized. 4.1.3 Because pulse interpolation equipment contains high speed counters and timers, it is important that equipment be installed in accordance with the manufacturers installation instructions, thereby minimizing the risk of counting spurious pulses caused by electrical interference occurring during the proving operation. The signal-to-noise ratio of the total sys-tem shall be adequately high to ensure that typical levels of electrical interference are rejected. Refer to Chapter 5.4, Chapter 5.5, and other sections of
