ã€Chinese Packaging Network News】Ultrasonic flowmeter to use the differential propagation speed method to achieve the measurement of water, due to site installation environment, pipe material and parameters, sensor installation and other factors, the accuracy of the measurement is often lower than its nominal value, sometimes The errors are relatively large. The relevant technical personnel have combined more than ten years of work experience to discuss the above-mentioned influencing factors. Only by eliminating various unfavorable factors can the measurement accuracy be improved.
1, the impact of the installation environment
During installation, the flowmeter generally requires upstream and downstream pipe sections with pipe diameters of 10 times and 5 times respectively to ensure that the flow state of the measured medium meets the accuracy requirements of the meter. When the field installation and use are performed, the installation position that meets the requirements cannot be usually found. . The lack of straight pipe leads to different measurement errors. The downstream straight pipe has little effect on the accuracy. When there are more than three times straight pipe on the upstream side, it can basically meet the needs of use. When the upstream straight pipe is not enough, such as after the elbow, valve and pump valve When loading a watch, it usually shows a positive error.
2, the influence of the input of pipeline parameters
After the ultrasonic flowmeter is installed, the instrument needs to input parameters such as pipe diameter and pipe wall thickness. If the pipe is fixed, the input parameters will be changed. The error of the pipe diameter input will increase the error of the measurement result by a factor of 2, and the wall thickness will be input. The error is positively correlated with the measurement error, but the effect on the measurement result is not significant.
3. Effect of Lining and Pipe Material
When measuring pipe material into the lining input error, it will also cause the calculation error of the probe installation distance, which will cause the ultrasonic incident angle to produce errors, reduce the measurement accuracy, and affect the signal and setting in severe cases, and thus cannot be measured. The effect of pipe 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, the flow rate converted by the flow velocity is correspondingly small, and the measurement error is proportional to the change in the pipe cross-sectional area. If the lining is too thick and the setting is neglected or there is a gap with the pipe wall, detection or signal errors usually occur. Therefore, the lining material and thickness should be accurately entered during the measurement. The effect of the pipeline and the inner lining on the measurement is reflected in the difference in the propagation speed of the sound waves in various media. If the actual sound velocity of the material is greater than the set sound velocity, the measurement result will be smaller, and vice versa.
4, sensor installation
According to different measuring environments and measuring probes, it can be divided into Z method, V method, X method, etc. The selection principle of the measuring sensor installation method is: when the water flows parallel along the tube axis, it is selected by Z method; when the flow direction and the pipeline axis When the installation interval of the transducer is not parallel or where the pipeline installation site is limited, the V method and the X method are used. The accuracy of the V method is higher than that of the Z method without affecting the signal reception. The distance between the two sensors has strict requirements, must be installed according to the required size, different installation spacing has different effects on the measurement accuracy, and some even have a large error.
5. Other external factors, coupling agents, signal cables
Ultrasonic flowmeter operating characteristics and the impact of the portable ultrasonic flowmeter measurement error analysis, we can see that to ensure the accuracy of the flowmeter measurement, we must also pay attention to the following points:
The wall surface of the sensor installation is polished clean; the sensor installation position should be in the plane of the bending axis of the upstream bend as much as possible to obtain the average value of the bend pipe after the smooth distortion; the sensor installation site and the reflection of the wall must avoid the interface And the weld; the pipe lining and scale layer at the sensor installation should not be too thick; the coupling agent must be used.
