Ultrasonic flow sensor installation requirements

- Jun 10, 2019-

Ultrasonic flowmeter uses the propagation velocity difference method to measure the water volume. Due to the influence of factors such as the installation environment, pipeline material and parameters, sensor installation, etc., the accuracy of measurement is often lower than its nominal value, sometimes the error is large, OSENON The technicians combined with more than ten years of work experience to discuss the above-mentioned influencing factors, and only by eliminating various unfavorable factors can the measurement accuracy be improved.

The principle of ultrasonic flow meter

1, the impact of the installation environment

During installation, it is generally required that the upstream and downstream flowmeters have straight pipe sections with 10 times and 5 times the diameter of the pipe to ensure that the flow state of the tested medium meets the accuracy requirements of the instrument. When the site is installed and used, it is often impossible to find a suitable installation location. . Insufficient straight pipe sections lead to different measurement errors. The downstream straight pipe has less influence on accuracy. When the upstream side has more than three times of pipe diameter straight pipe, it can basically meet the use. When the upstream straight pipe section is not enough, such as after the elbow, valve and pump valve When loading a watch, it generally shows a positive error.

2, the impact of pipeline parameter input

After the ultrasonic flowmeter is installed, the instrument needs to input parameters such as pipe diameter and pipe wall thickness. When the pipe is fixed, the input parameters are changed. The error of the pipe diameter input, the error of the measurement result will be expanded by 2 times, and the pipe wall thickness is input. The error is positively correlated with the measurement error, but the impact on the measurement results is not very large.

3, the impact of the lining and pipe material

When measuring the input material of the pipe into the liner, the calculation error of the installation distance of the probe will cause errors in the incident angle of the ultrasonic wave, which will reduce the measurement accuracy and affect the signal and setting in a serious case, so that it cannot be measured. The influence of the pipeline lining on the measurement is mainly due to the change of the actual pipe diameter. The lining reduces the cross-sectional area of the water. The flow rate converted by the flow rate is correspondingly small, and the measurement error is proportional to the change of the cross-sectional area of the pipe. When the lining is thick and the setting is neglected or there is a gap with the pipe wall, the detection or signal error generally occurs. Therefore, the lining material and thickness should be accurately input according to the actual measurement. The influence of pipeline and lining on the measurement is reflected in the difference of the propagation speed of sound waves in various media. If the actual sound velocity of the material is greater than the set sound velocity, the measurement result is small, otherwise it is too large.

4, sensor installation

According to the measurement environment and the measurement probe, it is divided into Z method, V method, X method, etc. The selection principle of the measurement sensor installation method is: when the water flows in parallel along the tube axis, the Z method is selected; when the flow direction and the pipeline axis When the non-parallel or pipeline installation location limits the installation interval of the transducer, the V method and the X method are used, and the V method measurement accuracy is higher than the Z method without affecting the signal reception. The distance between the two sensors has strict requirements, and must be installed according to the specified size. Different installation spacings have different effects on measurement accuracy, and some even have large errors.

5. Other external factors, coupling agents, signal cables

In the operation characteristics of the ultrasonic flowmeter and the error analysis of the influence of the portable ultrasonic flowmeter measurement, it can be seen that to ensure the accuracy of the flowmeter measurement to a large extent, the following points must also be noted:
The wall surface of the sensor installation is cleaned; the installation position of the sensor should be as close as possible to the curved axis of the upstream elbow to obtain a close average value after the smooth distortion of the elbow; the sensor installation and the wall reflection must avoid the interface. And welds; the pipe lining and scale layer at the sensor installation should not be too thick; the coupling agent must be used.

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