1. The influence of the installation environment
During installation, the upstream and downstream of the flowmeter are generally required to have straight pipe sections 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. During on-site installation and use, it is often impossible to find 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 the upstream side has more than three times the pipe diameter, it can basically meet the use. When the upstream straight pipe section is not enough, such as after elbows, valves, and pump valves When installing the watch, it generally shows a positive error.
2. The influence of pipeline parameter input.
After the 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 pipe wall thickness input The error is positively correlated with the measurement error, but it does not have a great influence on the measurement result.
3. The influence of lining and pipe material
When 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 relatively small. The measurement error is proportional to the change in the cross-sectional area of the pipeline. When 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.
4. Sensor installation
According to the difference of measurement environment and measurement probe, it can be divided into Z method, V method, X method, etc. The selection principle of measuring sensor installation method is: when water flows parallel to the pipe axis, choose Z method to install; when the flow direction is aligned with the pipeline axis When the transducer installation interval is restricted due to the non-parallel or pipeline installation location, 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 on 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.
5. Other external factors, couplants, signal cables
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 to ensure the accuracy of the flowmeter measurement to the greatest extent, the following points must be paid attention to:
The wall surface where the sensor is installed is polished clean; 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 place and the pipe wall reflection must avoid the interface And the weld seam; the pipe lining and scale layer where the sensor is installed should not be too thick; the couplant must be used.