The ultrasonic flowmeter uses the differential propagation method to measure the water volume. Due to the influence of the on-site installation environment, pipe materials and parameters, sensor installation and other factors, its measurement accuracy is often lower than the nominal value, and sometimes the error is large. Only by eliminating various unfavorable factors, in order to improve its measurement accuracy.
First, the impact of the installation environment.
In the installation process, in order to ensure that the flow state of the measured medium meets the measurement accuracy requirements, it is generally required that there are straight pipe sections with a diameter of 10 times or more than 5 times the diameter of the flowmeter. installation location. Insufficient straight pipe section causes different measurement errors, while the downstream straight pipe section has little effect on the accuracy. When the diameter exceeds three times, the upstream straight pipe section can basically meet the needs of use. When the upstream straight pipe section is insufficient, such as in elbows, valves , After the pump valve is installed on the meter, it is generally displayed as a positive error.
Second, the influence of the input value of the pipeline parameters.
After the ultrasonic flowmeter is installed, the meter needs to input parameters such as pipe diameter and pipe wall thickness. When the pipe is fixed, change the input parameters to increase the input error of the pipe diameter by 2 times, and the input error of the pipe wall thickness is proportional to the measurement error. , but has little effect on the measurement results.
Third, the influence of lining material and pipe material.
The wrong measurement of the input amount of the pipe lining will also lead to an error in the calculation of the installation distance of the probe, resulting in an error in the incident angle of the ultrasonic wave, reducing the measurement accuracy, and in severe cases affecting the signal and settings, making it impossible to measure. The influence of pipeline and lining quality on the measurement is mainly reflected in the difference of sound wave propagation speed in different media. If the actual sound speed of the material is greater than the set value, the measurement result will be too small, otherwise it will be too large.
Fourth, the installation of the sensor.
According to the different test environments and test probes, the sensor installation can be divided into Z method, V method, X method, etc. The selection principle of the sensor installation method is: when the water flows in parallel along the axial direction of the pipe, choose the Z method for installation; when the water flow When the direction is not parallel to the axial direction of the pipeline or the installation position of the pipeline limits the installation interval of the transducer, the Z method is selected for installation. The measurement accuracy of the V method is higher than that of the Z method without affecting the signal reception.
Fifth, other external factors such as couplants, signal lines, etc.
The working characteristics of the ultrasonic flowmeter and its influence on the measurement of the portable ultrasonic flowmeter are analyzed, and it is pointed out that in order to maximize the measurement accuracy of the flowmeter, the following points must be paid attention to:
The wall where the sensor is installed is polished; the sensor should be installed as far as possible in the bending axis of the upstream elbow to obtain a closer average value after the lossy deformation of the elbow; the sensor installation and the pipe wall The reflector must avoid interfaces and welds; the pipe lining and anti-fouling layer where the sensor is installed should not be too thick; couplant must be used.