Measurement Accuracy and Installation Analysis of Orifice Flow Meter

Abstract: The measurement accuracy and installation analysis information of the orifice flowmeter are provided by the excellent flowmeter and flowmeter manufacturers and quotation manufacturers. When the orifice flowmeter is used, the error of the measurement result is often caused by some objective factors such as installation or transportation errors. The following will mainly introduce the main measures to ensure the measurement accuracy of the orifice flowmeter: 1 . Reynolds number correction, . More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following is the details of the measurement accuracy and installation analysis of the orifice flowmeter. When the orifice flowmeter is used, the error of the measurement results is often caused by some objective factors such as installation or transportation errors. The following will mainly introduce the main measures to ensure the measurement accuracy of the orifice flowmeter: 1 .Reynolds number correction, there is a definite relationship between the flow coefficient of the orifice flowmeter and the Reynolds number. When the mass flow changes, the Reynolds number changes proportionally, thus causing the flow coefficient to change. 2. The orifice flowmeter is calibrated one by one. As long as the standard orifice plate is designed and manufactured with reference to relevant standards, it can be used directly without real flow calibration. Because the outflow coefficient can be calculated directly by the software, the computer calculation is ideal after all, and it is still different from the on-site environment. Therefore, in order to ensure the measurement accuracy, it is recommended to perform real flow calibration for each flowmeter, and the calibrated outflow The coefficients are compared with the calculation results, and the difference is calculated and corrected. 3. The influence of temperature on the orifice flowmeter and its correction. The change of fluid temperature causes the change of density, which leads to the change of the relationship between differential pressure and flow rate. The correction of temperature change is to use a temperature instrument to measure the on-site temperature and then input it into the secondary instrument to correct the error caused by the temperature change. 4. Swellability correction. When the orifice flowmeter measures the flow of steam and gas, the expansion of the fluid must be corrected. For the specific correction coefficient, please refer to the design manual of the throttling device. 5. Calculation of steam mass flow, when the orifice flowmeter measures steam, the flow value is first obtained from the differential pressure signal, and then the density is obtained from the steam temperature and pressure value to calculate the steam flow quality. Analysis of installation error of orifice flowmeter 1. Pipeline conditions: (1) The straight pipe section before and after the throttling piece must be straight, and there must be no visible bending. (2) The straight pipe section used to install the throttling should be smooth. If it is not smooth, the flow coefficient should be multiplied by the roughness to correct the sparseness. (3) In order to ensure that the flow of the fluid forms a fully developed turbulent velocity distribution 1D before the throttling member, and make this distribution into a uniform axisymmetric shape, so 1) the straight pipe section must be round, and the throttling must be round. In the 2D range before the piece, the roundness requirements are very strict, and there are certain roundness indicators. Specific measurement method: (A) On the OD, D/2, D, 2D 4 vertical pipe sections before the throttling piece, measure at least 4 single measurement values ​​of the inner diameter of the pipe with a large to equal angular distance, and take the average value D. The difference between the single measured value of any inner diameter and the average value shall not exceed±0.3% (B) After the throttling piece, use the above method to measure 8 single measurement values ​​of inner diameter at the OD and 2D positions. Comparing any single measurement value with D, the maximum deviation shall not exceed±2% 2) A long enough straight pipe section is required before and after the throttling piece. This long enough straight pipe section is related to the form of the local resistance piece before the throttling piece and the diameter ratio.βFor related, see Table 1 (β=d/D, d is the opening diameter of the orifice plate, and D is the inner diameter of the pipe). (4) The length of the straight pipe section between the resistance member and the second resistance member on the upstream side of the throttling member can be in the form of the second resistance member andβ=0.7 (regardless of the actualβWhat is the value) Take 1/2 of the value listed in Table 1 (5) The upstream side of the throttle is the open space or diameter≥In the case of a 2D large container, the straight pipe length between the open space or the large container and the throttle shall not be less than 30D (15D). If there are other local resistance parts between the throttle and the open space or the large container, the In addition to the minimum straight pipe length 1 specified in Table 1, the total length of the straight pipe from the open space to the throttling element shall not be less than 30D (15D). The minimum straight pipe section length on the upstream and downstream sides of the throttling piece Table 1 The form of the local female part on the upstream side of the throttling piece and the minimum straight pipe section length L Note: 1. The above table is only for standard throttling devices, and can be used for special throttling devices For reference 2. The number of columns is a multiple of the inner diameter D of the tube. 3. The numbers outside the parentheses in the above table are“Additional relative limit error is zero”, the numbers in parentheses are“The additional relative limit error is±0.5%”value of . That is, when there is a value in parentheses in the length of the straight pipe, the limit relative error τQ/Q of flow measurement. It should be added arithmetically by 0.5% i.e. (τQ/Q+0.5)

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