Factors Affecting the Measurement Accuracy of Orifice Flowmeter

Influence of measured fluid characteristics: Due to the nature of natural gas itself, it will undergo complex changes with the change of external ambient temperature, thus affecting the measurement accuracy of the flowmeter. For the measurement of natural gas, the working temperature and pressure of natural gas must be determined first, because the change of external temperature will cause the pressure and temperature of natural gas itself to change, which may cause excessive density changes and compression coefficient changes. Low-density gas presents difficulties for some measurement methods. At this time, it is necessary to change the selected measurement method, or make temperature and (or) pressure corrections to ensure the accuracy of the measurement.

Influence of instrument performance: The main causes of errors caused by the orifice flowmeter itself are: the sharpness of the right angle of the orifice inlet; the pipe diameter size does not match the calculation; the orifice thickness error; the throttling device accessories produce steps and eccentricity; the flatness of the upstream end face of the orifice of the orifice flowmeter; the ring chamber size produces steps and eccentricity; the pressure taking position; welding, weld protrusion; the pressure taking hole is not processed in a standardized or blocked manner; the throttling device is not axially consistent, etc. These factors may affect the repeatability of the orifice plate, which is determined by the principle and manufacturing quality of the instrument itself, and it is an important indicator in process control applications. In addition to repeatability, accuracy is also related to the value calibration system. In practical applications, the excellent repeatability of the instrument is disturbed by many factors, including changes in fluid viscosity, density, etc., which will affect the measurement accuracy. If the output characteristics of the instrument are nonlinear, this effect is more prominent.

The impact of flow meter installation: The installation error caused by the deviation of the pipeline layout is universal, and the main reason for its occurrence is that the length of the straight pipe section cannot be met on site.

The impact of environmental conditions: Although the flow meter can be installed and used normally, some performance parameters and hardware aspects of the instrument have also changed due to changes in the environmental conditions used and the expected situation, which will change the flow meter measurement results. The reason why the orifice flowmeter is easy to deviate from the standard is the working principle and structural characteristics of the instrument itself. The instrument's own errors are generated during manufacturing, and the installation and use errors are caused by corrosion, wear, and contamination of the fluid medium during installation or long-term use. Therefore, the flow metering system should be installed strictly according to technical requirements to eliminate installation errors.

The orifice flowmeter is a high range ratio differential pressure flow device that combines a standard orifice plate with a multi-parameter differential pressure transmitter (or differential pressure transmitter, temperature transmitter and pressure transmitter). It can measure the flow of gas, steam, liquid and natural gas, and is widely used in process control and measurement in the fields of petroleum, chemical industry, metallurgy, electricity, heating, water supply, etc. In order to speed up the progress of the test, it is recommended to introduce advanced foreign online gas chromatography systems and flow computers, and develop a natural gas energy metering system suitable for my country's national conditions on the basis of digesting the imported technology. (end)