1. The influence of the installation environment
During installation, it is generally required that the upstream and downstream of the flowmeter have straight pipe sections with a diameter of 10 times and 5 times more, respectively, to ensure that the flow state of the measured medium meets the accuracy requirements of the instrument. When installing and using on-site, it is often impossible to find an installation location that meets the requirements. . Insufficient straight pipe section leads to different measurement errors. The downstream straight pipe is expected to have little effect on the accuracy. When the upstream side has a straight pipe with more than three times the pipe diameter, it can be basically used. When the upstream straight pipe section is not enough, such as after the elbow, valve, pump valve When installing the watch, it generally shows a positive error.
2. The influence of pipeline parameter input.
After the ultrasonic flow meter is installed, the meter needs to input parameters such as pipe diameter and pipe wall thickness. If the input parameters are changed when the pipe is fixed, the error of the pipe diameter input will increase the error of the measurement result by 2 times, and the pipe wall thickness input will be doubled. The error is positively correlated with the measurement error, but has little effect on the measurement result.
3. Influence of lining and pipe material
When the measuring pipe material is input incorrectly into the lining, it will also cause an error in the calculation of the installation distance of the probe, which will cause an error in the incident angle of the ultrasonic wave, reduce the measurement accuracy, and in severe cases, affect the signal and settings, so that the measurement cannot be performed. The influence of the pipe lining on the measurement is mainly due to the change of the actual pipe diameter caused by it. 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 of the pipe cross-sectional area. If the lining is too thick and is ignored when setting or there is a gap with the pipe wall, detection or signal error generally occurs, so the lining material and thickness should be accurately and accurately input during measurement. The influence of pipeline and lining quality 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 will be small, and vice versa.
4. Sensor installation
According to the different measurement environments and measurement probes, it is divided into Z method, V method, X method, etc. The selection principle of the installation method of the measurement sensor is: when the water flows parallel to the pipe axis, choose the Z method for installation; when the flow direction is parallel to the pipeline axis When the installation distance of the transducer is limited by the non-parallel installation site or the installation location of the pipeline, 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. The distance between the two sensors has strict requirements, and must be installed according to the specified size. Different installation distances have different effects on the measurement accuracy, and some even have large errors.
5. Other external factors, couplants, signal cables
From the analysis of the operating characteristics of the ultrasonic flowmeter and the error analysis of the impact on the measurement of the portable ultrasonic flowmeter, it can be seen that in order to maximize the accuracy of the flowmeter measurement, the following points must also be paid attention to:
The wall surface of the sensor installation site should be polished clean; the sensor installation position should be as close as possible to the bending axis plane of the upstream elbow, so as to obtain a closer average value after the elbow is smoothly distorted; the sensor installation location and the reflection part of the pipe wall must avoid the interface and welding seam; the pipe lining and scale layer where the sensor is installed should not be too thick; couplant must be used.