Fixed ultrasonic flowmeter uses the differential propagation velocity method to measure the amount of water. Due to the influence of on-site installation environment, pipeline material and parameters, and sensor installation, the accuracy of measurement is often lower than its nominal value, sometimes the error is large. Based on more than ten years of work experience, the manufacturer discussed the above-mentioned influencing factors. Only by eliminating various unfavorable factors can the measurement accuracy be improved.
1, sensor installation
Ultrasonic flowmeter can be divided into Z method, V method, X method, etc. according to different measuring environments and measuring probes. The selection principle of the measuring sensor installation method is: When the water flows parallel along the tube axis, choose Z method to install; when the flow direction When the pipeline axis is not parallel or the installation place of the pipeline limits the installation interval of the transducer, 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.
2, the influence of the input of pipeline parameters
　 After the fixed ultrasonic flowmeter is installed, the instrument needs to input parameters such as pipe diameter and pipe wall thickness. If the pipeline is fixed and the input parameters are changed, 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 the impact on the measurement result is not great
3, the impact of the installation environment
When stationary ultrasonic flowmeters are installed, it is generally required that the flowmeters have 10 and 5 times straight pipe sections upstream and downstream, respectively, to ensure that the flow state of the measured medium satisfies the accuracy requirements of the instrument. When installed on the spot, they are often not found. Meet the required installation location. Insufficient straight pipe leads to different measurement errors, and the downstream straight pipe has little effect on accuracy. When there are more than three times straight pipe on the upstream side, it can basically satisfy the 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.
4. 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 caused by 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.
5. Other external factors, coupling agents, signal cables
The operating characteristics of the fixed ultrasonic flowmeter and the error analysis of the impact of the portable ultrasonic flowmeter measurement can be seen, 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 should be installed as far as possible in the plane of the bending axis of the upstream bend to obtain the average value closer to the smooth distortion of the bend; the sensor installation and the wall reflection must avoid the interface and weld; sensor installation The pipe lining and scale layer should not be too thick; the coupling agent must be used.
Fixed Ultrasonic Flowmeter - Jiangsu Huawei Yuanhang Automation Instrument Co., Ltd.
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