Abstract: the device has the function of scale steam flowmeter calibration gas flow measurement uncertainty evaluation information produced by excellent flow meter
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Abstract: based on critical flow venturi nozzle method of gas flow standard device, briefly expounds the master meter method which has the function of the steam flowmeter calibration gas flow standard device measurement uncertainty evaluation methods and steps.
1, the gas flow standard device is introduced.
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By the method of critical flow venturi nozzle gas flow standard device, briefly expounds the master meter method which has the function of the steam flowmeter calibration gas flow standard device measurement uncertainty evaluation methods and steps.
1, gas flow standard device is introduced standard table method flow standard device in a standard flow meter as the standard, make the fluid continuous and checked with standard flowmeter flowmeter, comparing both the output of the instantaneous flow values, or over a period of time accumulated flow value, to determine the spare parts of flowmeter metering performance.
Critical flow sonic nozzle gas flow standard device, as a kind of typical standard table method of gas flow standard device, mainly composed of gas source, test line, parallel critical flow sonic nozzle group and the control equipment of four parts.
Company was built in 2007 a set of table based on sonic nozzle set of critical flow of gas flow standard device, device as two kinds of medium flow meter common compressed air and steam flow standard, used in the design of zui for scientific and authoritative steam flow measurement, the mathematical model of temperature and pressure compensation, through gas flow device and steam flow measurement of yantai testing station flow standard device than real flow calibration, data fitting processing, ensure accurate and reliable to achieve the steam flowmeter calibration.
2, gas flow standard device, the uncertainty evaluation of 2.
A mathematical model of the device adopts critical flow sonic nozzle as a standard table, fluid medium is air, the quality of its actual individual sound critical flow nozzle qm and volume flow qv calculation formula is: type: & rho;
, p, T, respectively detected flowmeter in air density (
, absolute pressure (
And thermodynamic temperature (
Nozzle throat area;
The nozzle flow coefficient;
Critical flow function;
The stagnation pressure of the gas before the nozzle (
The stagnation temperature of the gas before the nozzle (
The universal gas constant, its value is 8314.
Thousand of moab air quality, its value is 28.
As a standard table method of gas flow standard device, this device using multiple critical flow sonic nozzle (
The standard meter)
Parallel method, the accumulative flow through each of the critical flow sonic nozzle gas flow to expand device gas flow range.
Since each critical flow sonic nozzle is working independently, so after n sound critical flow nozzle parallel combination device for gas flow measurement uncertainty can be said,
Type can be concluded that multiple critical flow after the sonic nozzle parallel combination will not reduce the uncertainty of measurement standard device, the device measurement uncertainty must not exceed the nozzle set single critical flow in sonic nozzle gas flow zui large value of the uncertainty.
Therefore, can according to the type (
Mathematical model, through the evaluation of a single critical flow sonic nozzle gas flow uncertainty method, determine the multiple critical flow sonic nozzle device after combination gas flow measurement uncertainty.
2 standard evaluation of uncertainty of input because of verification and using sonic nozzle is in the air medium, A, C *, M and R values are the same, so can ignore this 4 introduce uncertainty.
The uncertainty of outflow coefficient C in accordance with the JJG620 -
2008 'critical flow venturi nozzle verification regulation requirements, under the confidence probability of 95%, U = 0.
For measuring frequency is 6, available t95 = 2.
45, has (
Sonic nozzle at the entrance of stagnation pressure P0 used by the uncertainty of pressure transmitter
full scale is 1000 kpa, permissible error for the full range of 0.
1%, therefore, when P0 take 800 kpa, according to the uniform distribution, is (
Sonic nozzle at the entrance to the stagnation temperature T0 the uncertainty of the full range of 100 ℃, temperature transmitter used permissible error for the full range of 0.
Considering stagnation container temperature non-uniformity (
Influence, therefore, when T0 take 300 k, according to the uniform distribution, 90% reliable, have (
Detected flowmeter at temperature T and pressure P of the uncertainty of this device was temperature T and pressure P the meter measuring instrument and measuring sonic nozzle inlet stagnation temperature and pressure at the same instrument, considered separately calibrating temperature non-uniformity in the pipeline is 0.
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