The fixed ultrasonic flowmeter uses the propagation velocity difference method to measure the water volume. Due to the influence of the on-site installation environment, pipe material and parameters, sensor installation and other factors, the accuracy of the measurement is often lower than its nominal value, and sometimes the error is large. Based on more than ten years of work experience, the manufacturer has discussed the above-mentioned influencing factors. Only by eliminating various unfavorable factors can the measurement accuracy be improved.1. Sensor installationUltrasonic flowmeters are divided into Z method, V method, X method, etc. according to the measurement environment and measurement probe. The selection principle of the measurement sensor installation method is: when the water flows parallel to the pipe axis, select the Z method to install; when the flow direction When it is not parallel to the pipeline axis or the installation location of the pipeline restricts the installation interval of the transducer, the V method and the X method are used. The measurement accuracy of the V method is higher than that of the Z method without affecting the signal reception. There are strict requirements for the distance between the two sensors, and they must be installed according to the specified size. Different installation distances have different effects on the measurement accuracy, and some even have large errors.2. The influence of pipeline parameter inputAfter the fixed ultrasonic flowmeter is installed, the meter needs to input the pipe diameter, pipe wall thickness and other parameters. Change the input parameters when the pipe is fixed. The error of the pipe diameter input will increase the error of the measurement result by 2 times. The thickness input error is positively correlated with the measurement error, but it does not have a great influence on the measurement result.3. The influence of the installation environmentWhen a fixed ultrasonic flowmeter is installed, it is generally required that the upstream and downstream of the flowmeter have straight pipes with diameters of 10 times and 5 times or more respectively to ensure that the flow pattern of the measured medium meets the accuracy requirements of the instrument. It is often not found when installed and used on site. An installation location that meets the requirements. Insufficient straight pipe sections lead to different measurement errors. The downstream straight pipe hopes to have less impact on accuracy. When there are more than three times the pipe diameter on the upstream side, the straight pipe can basically satisfy the use. When the upstream straight pipe section is not enough, such as after elbows, valves, and pump valves When the watch is installed, it generally shows a positive error.4. The influence of lining and pipe materialWhen the input of the measuring pipe material into the lining is wrong, it will also cause an error in the calculation of the installation distance of the probe, which will cause an error in the ultrasonic incident angle, reduce the measurement accuracy, and affect the signal and settings in severe cases, making it impossible to measure. The influence of the pipeline lining on the measurement is mainly due to the change in the actual pipe diameter. The lining reduces the cross-sectional area of the water, and the flow rate converted by the flow rate is correspondingly small. The measurement error is proportional to the change in the cross-sectional area of the pipeline. If the lining is too thick and is ignored when it is installed or there is a gap with the pipe wall, detection or signal errors will generally occur. Therefore, the lining material and thickness should be accurately input when measuring. The influence of the quality of the pipeline and the inner lining on the measurement is reflected in the difference in the propagation speed of sound waves in various media. If the actual sound speed of the material is greater than the set sound speed, the measurement result is too small, and vice versa.5. Other external factors, couplants, signal cablesThe operating characteristics of the fixed ultrasonic flowmeter and the error analysis of the impact on the measurement of the portable ultrasonic flowmeter, it can be seen that to ensure the accuracy of the flowmeter measurement to the maximum extent, the following points should be paid attention to: The wall surface where the sensor is installed Polished cleanly; the installation position of the sensor should be as far as possible in the bending axis plane of the upstream elbow, to obtain a closer average value after the smooth distortion of the elbow; the sensor installation and the reflection of the pipe wall should avoid interfaces and welds; the sensor The pipe lining and scale layer at the installation place should not be too thick; the coupling agent must be used.
Post time: 21-09-21