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# Analysis of Uncertainty of Membrane Gas Meter

by：Sure     2021-07-30
The basic error of the diaphragm gas meter is measured by the bell-type gas flow standard device, the volume of gas discharged from the standard device through the diaphragm gas meter, and the gas pressure and temperature in the device and in front of the diaphragm gas meter are measured and calculated The actual value Vm of the gas volume of the diaphragm gas meter is calculated according to the mathematical model: where: Vsn flows through the diaphragm gas meter. The basic error of the actual diaphragm gas meter is measured by the bell-type gas flow standard device. The volume of gas discharged from the standard device through the diaphragm gas meter, and the gas pressure and temperature in the device and in front of the diaphragm gas meter are measured, and the actual value Vm of the gas volume of the diaphragm gas meter is calculated, and the mathematical model is obtained according to the calculation formula : In the formula: Vsn——the actual volume value flowing through the diaphragm gas meter (corrected by temperature, pressure, etc.), L; Vs——the actual volume value given by the bell jar, L; Ts——in the verification clock cover The temperature of the gas, ℃; Tm——the temperature of the gas in the gas meter at the time of verification, ℃; Ps——the pressure of the gauge in the calibration clock cover, Pa; Pm——the pressure of the gas in the gas meter at the time of verification, Pa. Pa——Atmospheric pressure during verification, Pa. The diaphragm gas meter is verified with a gas bell-type gas flow standard device, and the pressure in the gas bell is about 1000Pa, and the pressure of the diaphragm gas meter is about 900Pa. 1. Uncertainty of standard device Verification of the uncertainty of the standard F-standard device used in diaphragm gas meters is Ur(Vs)u003d0.5%, ku003d2. In the mathematical model formula, the partial derivative of Vs is calculated, and the relative sensitivity coefficient is cr(Vs)»1. According to the normal distribution, the standard uncertainty of type B of the device is obtained. 2. The uncertainty of the resolution of the diaphragm gas meter is once The gas volume that has passed the verification is 100L, the resolution of the tested membrane gas meter is 0.2L, and the relative sensitivity coefficient Cr(Vm)»1 is calculated according to the rectangular distribution, and the U2 of the Class B uncertainty is obtained. 3. Clock cover watch The maximum allowable error of the pressure Ps measurement uncertainty Ps is ±10Pa, and the relative sensitivity coefficient is calculated according to the rectangular distribution, then Ut(Ps)u003d10/1000»1.0%, and the type B uncertainty U3 is obtained. This item is almost negligible. 4. The maximum allowable error of measurement uncertainty Pm of the diaphragm gas meter is ±10Pa. In the mathematical model, Vm is the partial derivative of Pm, and the relative sensitivity coefficient is Ur(Pm)u003d10/1000u003d1%, u200bu200baccording to the rectangle Distributed calculation, the uncertainty of type B u4 is obtained. This item is almost negligible. 5. The measurement uncertainty of atmospheric pressure uses a vibrating cylinder barometer to measure the atmosphere. The allowable error is 50Pa, then ur(Pa)u003d50/100000u003d0.05%, which is considered as a rectangular distribution. From the actual measurement, Pemu003d1000Pa, the relative sensitivity coefficient is calculated according to the rectangular distribution, and the type B uncertainty u5 is obtained. This item can be ignored. 6. The maximum allowable error of the temperature measurement uncertainty Tm in the diaphragm gas meter is ±0.1℃. In the mathematical model, Vsn is the partial derivative of Tm, and the relative sensitivity coefficient is ur(Tm)u003d0.11293u003d0.34%, according to the rectangle Distributed calculation, the uncertainty of type B u6 is obtained. This item is almost negligible. 7. The maximum allowable error of the temperature measurement uncertainty Ts in the bell jar is ±0.1℃. In the mathematical model formula, Vsn calculates the partial derivative of Ts, and the relative sensitivity coefficient is ur(Tm)u003d 0.1/293u003d0.34%, according to the rectangle Distributed calculation, the uncertainty of type B u7 is obtained. This item is almost negligible. 8. Uncertainty of measurement repeatability E The membrane gas meter performs 6 independent measurements at each flow point, and calculates the error of each flow point according to the Bessel formula to obtain the standard uncertainty of Type A, and takes the maximum value, ur( Emax)u003d0.4%. Calculate according to the rectangular distribution, and get the uncertainty of type B u8. 9. Synthetic standard uncertainty Uc (square and root of the component) 10. Expanded uncertainty U (ku003d2) 11. Calibration and verification of diaphragm gas meters Measurement Uncertainty Analysis Table
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