Factors affecting the measurement accuracy of ultrasonic flowmeter

1. The effect of the upstream and downstream straight pipe sections on the measurement accuracy of the ultrasonic flowmeter. The calibration coefficient K is a function of the Reynolds number. Fluid flows from laminar flow to turbulent flow, and the velocity distribution is uneven. The calibration coefficient K will produce a large change, resulting in a decrease in measurement accuracy. According to the use requirements, the ultrasonic flowmeter transducer should be installed in the position where the upstream straight pipe section is 10D and the downstream straight pipe section is 5D. , The farther the noise source and the ray source, the better. " If there are pumps, valves and other equipment upstream of the installation location of the ultrasonic flowmeter transducer, the straight pipe section is required to be above 30D. Therefore, the length of the straight pipe section is the main factor to ensure the accuracy of the measurement.

2. The influence of pipeline parameter equipment on the measurement accuracy of the ultrasonic flowmeter. The accuracy of the pipeline parameter setting is closely related to the measurement accuracy. If the setting of the pipe material and size is not consistent with the actual situation, it will cause an error in the theoretical pipe flow cross-sectional area and the actual flow cross-sectional area, resulting in inaccurate final results. In addition, the transmission distance between the ultrasonic flowmeter transducers is based on the results of comprehensive calculation of various parameters such as fluid (sound velocity, dynamic viscosity), pipeline (material and size), transducer installation method, etc. Deviations in distance can also cause large measurement errors. Among them, the setting and installation distance of the internal warp of the pipeline have a significant influence on the measurement accuracy. According to relevant data, if the error in the pipeline is ± 1%, it will cause a flow error of about ± 3%; if the installation distance error is ± 1mm, it will produce a flow error within ± 1%. It can be seen that only when the pipeline parameters are set correctly, the ultrasonic flowmeter can be installed accurately, reducing the influence of the pipeline parameters on the measurement accuracy.

3. The influence of the installation position of the ultrasonic flowmeter transducer on the measurement accuracy. There are two ways to install the transducer: reflective and direct. If the direct sound installation uses a short sound speed, the signal strength can be enhanced.

4. The influence of the coupling agent on the measurement accuracy. In order to ensure full contact with the pipeline, it is necessary to apply a layer of coupling agent evenly on the surface of the pipeline when installing the transducer, the general thickness is (2mm-3mm). The bubbles and granules in the coupling agent are brought out, so that the emitting surface of the transducer is closely attached to the wall of the tube. Flowmeters for measuring circulating water are mostly installed in wells. The environment is humid and sometimes flooded. If a common coupling agent is used, it will fail in a short time and affect the measurement accuracy. Therefore, a special waterproof coupling agent must be selected. The coupling agent should be used within the validity period, generally 18 months. To ensure measurement accuracy, the transducer should be reinstalled and the couplant should be replaced every 18 months.

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