API MPMS 4.6-2021 pdf download.Manual of Petroleum Measurement Standards Chapter 4.6.
1 Scope This chapter describes how the double-chronometry method of pulse interpolation, including system operating requirements and equipment testing, is applied to meter proving. 2 Normative References The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For undated references, the latest edition of the reference document (including any amendments) applies. API MPMS Chapter 4.2, Displacement Provers 3? Terms? and? Defnitions For the purposes of this document, the following terms and defnitions apply. Terms of more general use may be found in the API MPMS Chapter 1, Online Terms and Defnitions Database. Acronyms are defned in the text at frst use. 3.1 detector signal A contact closure change or other signal that starts or stops a prover counter or timer and defnes the calibrated volume of the prover. 3.2 double-chronometry (dual chronometry) A pulse interpolation technique used to increase the discrimination level of fowmeter 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, associated logic, detector signals, and the fowmeter pulses. 3.3 fowmeter? discrimination A measure of the smallest increment of change in the pulses per unit of the quantity being measured. 3.4 frequency The number of repetitions, or cycles, of a periodic signal (e.g., pulses, alternating voltage, or current) occurring in a 1-second time period. The number of repetitions, or cycles, that occur in a 1-second period is expressed in hertz. 3.5 meter pulse continuity The deviation of the interpulse period of a fowmeter expressed as a percentage of a full pulse period.
3.7 pulse period The reciprocal of pulse frequency (i.e., a pulse frequency of 2 Hz is equal to a pulse period of 0.5 second). 3.8 pulse generator An electronic device that can be programmed to output voltage pulses of a precise frequency or time period. 3.9 pulse interpolation Any of the various techniques by which the meter pulses are counted between two events (such as detector switch closures), whereby any remaining fraction of a pulse between the two events is calculated. 3.10 rotating meter Any metering device for which the meter pulse output is derived from mechanical rotation as driven by the fowing stream. For example, turbine and positive displacement meters are metering devices for which the output is derived from the continuous angular displacement of a fow-driven member. 3.11 signal-to-noise ratio The ratio of the magnitude of the electrical signal to that of the electrical noise. 4 Double-Chronometry Pulse Interpolation 4.1 General Double-chronometry pulse interpolation requires counting the total integer (whole) number of fowmeter pulses, N m , generated during the proving run and measuring the time intervals, T 1 and T 2 . T 1 is the time interval between the frst fowmeter pulse after the frst detector signal and the frst fowmeter pulse after the last detector signal. T 2 is the time interval between the frst and last detector signals.
4.2 Conditions of Use 4.2.1 The interpolated number of pulses, N 1 , will not be a whole number. N 1 is therefore rounded of as described in API MPMS Chapter 12.2  . 4.2.2 Pulse interpolation methods are based on the assumptions that actual fow rate does not change substantially during the period between successive meter pulses, and each pulse represents the same volume (refer to API MPMS Chapter 4.2, Annex E). To maintain the validity of these assumptions, periodic fuctuations in the fow rate during the proving operation shall be minimized. 4.2.3 Because pulse interpolation equipment contains high-speed counters and timers, it is important that equipment be installed in accordance with the manufacturer’s installation instructions, thereby minimizing the risk of counting spurious pulses caused by electrical interference occurring during the proving operation. Refer to API MPMS Chapter 5.4  , API MPMS Chapter 5.5  , and other sections of API MPMS Chapter 4  for more details.