Orifice flowmeter calibration device and calibration method thereof
Through the development of the standard gauge gas flow standard device, the relationship between the flow rate and the pressure correction term of the orifice flowmeter is linearly fitted, and the standard curve of the flowmeter is obtained and the accuracy level is evaluated. The experimental results show the feasibility and reliability of the calibration method.
0. Introduction
There are many petroleum and chemical enterprises in Xinjiang, and nearly 100 thermal power plants of all sizes are located in various states of Xinjiang. For a long time, the atmospheric environment in Xinjiang has been under tremendous pressure. With the deepening of the development process in the western region and the strengthening of the comprehensive management of the atmospheric environment, more and more atmospheric environment samplers for detecting total suspended particulate matter, and the demand for calibration and calibration of the standard orifice flowmeter used therein are also increasing. . In this regard, the Xinjiang Metrology and Testing Institute has established a standard gauge gas flow standard device for calibration of orifice flowmeters .
Standard device
1.1 Composition
The standard gauge gas flow standard device uses a reproducible Roots flowmeter and a turbine flowmeter as the main standard, and is connected in series with the orifice flowmeter in the pipeline, equipped with two differential pressure transmitters and two temperatures. The transmitter selects different lines depending on the measurement range . The computer simultaneously collects the flow signals output by the checklist and the standard meter, and corrects the flow rate by using the pressure and temperature values ​​respectively, and obtains the corresponding standard flow rate, and then compares them to obtain the indication error of the flow rate indicated by the checklist and the instrument. Coefficient, the repeatability of the checked table is obtained by multiple measurements.
1.2 technical parameters
Measurement range: 2 ~ 200 m3 · h- 1; expansion apparatus of uncertainty: U = 0.5%, k = 2.
2. Calibration Method
1) under specified environmental conditions, according to HJ / T 368-2007 "total suspended particulates sampled calibration orifice flowmeter Used" Technical requirements and testing methods, the orifice flow meter installed in the meter method the gas flow device on. Check the air leak with air as the calibration medium . Use a rubber pad to block the orifice of the orifice flowmeter and turn on the air pump. The standard flowmeter within 20 s should have no reading change. Otherwise, check the leak position and eliminate the leaking fault until the standard flowmeter has no reading change. Remove the rubber pad and calibrate the orifice flow meter.
2) in the orifice flow meter flow rate range, a uniform flow selecting seven points. Start the air pump and adjust the flow to near each selected point 
Maintain the same flow. Start timing when the Roots flowmeter reads an integer value, record the Roots flowmeter initial reading Vi , read and record the Roots flowmeter differential pressure p ( Pa ) and the differential pressure of the orifice flowmeter orifice H ( Pa ), stop timing after the Roots flowmeter reading increases by at least 1 m3 , record the Roots flowmeter termination reading Vf and the measurement time t ( min ). Repeat the above steps to calibrate the selected seven flow points one by one.
3 ) Calculate the standard condition flow for each calibration point. The metering volume Vm through which the orifice flowmeter is passed is calculated from the Roots flowmeter reading :
4 ) Calculate the pressure difference correction term Y of each calibration point orifice flowmeter :
If the pL value of any calibration point exceeds ±2% , the data should be redoed as described above until the requirements are met . Those who cannot meet the requirements are not qualified.
3. Experimental data processing
Calibration of a well-stabilized orifice flowmeter produced by a company in Qingdao, flow rate range: 80 ~ 130 L · min-1 , accuracy level: 1 level. The experimental data is shown in Table 1 . Experimental field atm p1 = 93 500 Pa, the ambient temperature T1 = 293.65 K. The correction term Y and the nominal flow QN calculated according to the formula are linearly fitted in Excel software, and the zero point A=2.229 9 gain B=0.253 7 is obtained , and the correlation coefficient R2=0.998 3 , that is, the fitting function is: Ycal =0.253 7QN + 2.229 9 , as shown in Figure 2 . The data is processed and the results are shown in Table 2 .
It can be seen from Table 2 that the pL values ​​of the seven calibration points are not more than ±1% , and the calibration results are good.
4. Conclusion
The establishment of the orifice flowmeter calibration device provides a technical means for the calibration of the orifice flowmeter for the total suspended particulate sampler. The detection method and technical indicators meet the requirements of the Environmental Protection Administration HJ/T 368-2007 "calibration of total suspended particulate sampler The requirements of the orifice flowmeter. Experimental data demonstrates the feasibility and reliability of the standard device and calibration method.
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