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technical article
How to ensure the measurement accuracy of orifice flowmeters
2011-7-7 17:28:04

When the orifice plate flowmeter is measured on the spot, the measurement results often have large errors due to some objective factors. Below, I will introduce the main methods to ensure the accuracy of the orifice plate flowmeter .

1. Orifice flowmeters are calibrated one by one. Everyone knows that standard orifice plates can be used directly as long as they are designed and manufactured in accordance with relevant standards, without the need for actual flow calibration. Because the outflow coefficient can be directly calculated by the software, but the computer calculation is ideal after all, and there is still a certain difference from the field environment. Therefore, in order to ensure the measurement accuracy, it is still necessary to perform real-flow calibration on each orifice plate flowmeter and calibrate it. The outflow coefficient is compared with the calculation result, the difference is calculated and then corrected.

2. Reynolds number correction. There is a definite relationship between the flow coefficient of the orifice flowmeter and the Reynolds number. When the mass flow rate changes, the Reynolds number changes in proportion to the change in the flow coefficient.

3, the effect of temperature on the orifice flowmeter and its correction, changes in the density of the fluid caused by changes in the temperature of the fluid, resulting in changes in the relationship between differential pressure and flow rate, and secondly, changes in the temperature caused by changes in the inner diameter of the pipe, the orifice opening The correction of temperature change is to use a temperature meter to measure the temperature on the spot and then input it to the secondary meter to correct the error caused by the temperature change.

4. Swellability correction. When measuring the flow of steam and gas with an orifice flowmeter , the fluid's expandability must be corrected. For specific correction coefficients, refer to the throttle device design manual.

5. Calculation of steam mass flow rate. When the orifice flow meter measures steam, the flow rate value is obtained from the differential pressure signal, and then the density is calculated from the steam temperature and pressure value check table to calculate the steam flow mass.