Factors affecting the accuracy of orifice flowmeters and ways to improve them
Author:vacorda Source:vacorda.com Date: 2018-04-17 15:13:29
Orifice flowmeter is a high-range differential pressure flow device which is composed of a standard orifice plate and a multi-parameter differential pressure transmitter (or differential pressure transmitter, temperature transmitter and pressure transmitter). It can measure the flow of the gas, steam and liquid.
Advantages of the standard orifice plate flow meter
1. The standard orifice flowmeter belongs to the standard throttling device and has been approved by the international standard organization. It can be used without real-flow calibration;
2. The standard orifice flowmeter structure is simple, strong, stable and with reliable performance and cost-effective;
3. Standard orifice flowmeter has a wide range of applications, including all single-phase fluid (liquid, gas, steam), part of the mixed-phase flow, the general production process of the diameter, working temperature and pressure all can be measured.
The fundamental reason that influences the accuracy of the orifice plate flowmeter measurement is whether the geometry and flow conditions of the throttling device deviate from the design criteria. Therefore, in practical use, the throttling device, orifice plate, and double-ripple differential pressure gauge should be inspected and adjusted regularly in strict accordance with the design requirements, so as to reduce the measurement error and ensure the measurement accuracy.
Improving Measure Accuracy of Orifice Flowmeter
1. Pipeline requirements: The national standard has strict technical requirements for the length of the measuring pipe, straight pipe, roundness and internal surface roughness. When the minimum length of the buret does not meet the standard requirements, it will cause deviations in the flow measurement results. Its size is related to the aperture ratio β and Reynolds number. Therefore, a rectifier must be installed on the straight pipe in front of the orifice plate to ensure measurement accuracy.
2. Installation requirements: The inlet end face of the orifice must be perpendicular to the axis of the pipe, and the deviation cannot exceed 1 degree. When installing the orifice plate, it is necessary to pay attention to the direction of the pipeline, and it is strictly prohibited to install it reversely. It must meet the requirements of the standard for different axial tolerances. The gasket shall not be installed into the straight pipe section or the inner space of the pressure-receiving device, and shall not block the pressure-taking port and cause the change of the pressure-taking position. The new station must be installed in the throttling device after the pipeline has been purged and run for a few days to prevent the orifices from being damaged or contaminated by liquid and solid impurities in the gas.
3. To correctly select and use the differential pressure transmitter: the differential pressure measurement range is too large, the flow is small, and the differential pressure gauge works below 30%, which will greatly reduce the accuracy of flow measurement. When the flow is reduced, it must be replaced in time. Differential pressure gauge range spring or orifice specifications, otherwise differential pressure error will increase exponentially.
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