Matters needing attention in on-site verification of large-caliber electromagnetic flowmeter

1. Understand the field environment and the values ​​of the materials, tube outer diameter, wall thickness, fluid and fluid temperature of the pipeline to be inspected. The on-site inspection uses a high-precision thickness gauge to ensure the accuracy of the measurement.

2. The standard meter is installed in the straight pipe section. The converter is installed in the upstream straight pipe section for 10D, and the downstream straight pipe section is 5D to increase the flow rate. Avoid upstream and downstream disturbance sources (pumps, valves, elbows), and if necessary, consider adding a rectifier. When there are pumps, valves, etc. upstream, the length of the straight pipe section is preferably 30D. The standard watch cannot be installed in the tube and there is a gas position. The bubble will weaken the ultrasonic signal and affect the measurement accuracy. The converter is installed as much as possible by the V-type method to ensure that the sound path is on the pipe diameter plane to improve the measurement accuracy.

3. For straight pipe sections, the emitter of the ultrasonic flowmeter should be installed on the positive side of the pipe side to avoid the influence of sediment or bubbles.

4. During the verification process, the flow rate should not be less than 0.2m/s. The standard table is synchronized with the data acquisition by the comparison table, and the coefficient of the tested table is adjusted according to the measurement error. Set the appropriate acquisition interval according to the situation and extend the acquisition interval as much as possible. The use of software to save, display and print data, which can eliminate the additional errors caused by manual readings, improve the accuracy of on-site calibration and verification.

5. The verification result is affected by pressure and temperature. The temperature should be controlled indoors and on-site to make the temperature field of the verification system stable. Try to shorten the continuous pipeline distance between the flowmeter outlet and the volumetric tube inlet to reduce the pressure loss and temperature difference caused by the friction of the pipeline, so that the pressure and temperature of the flowmeter and the volumetric tube are as consistent as possible.

Since most of the large-diameter flowmeters are electromagnetic flowmeters or plug-in ultrasonic flowmeters, the instrument structure is mostly flanged or inserted into the pipeline. It is only allowed to be disassembled when the flow is stopped, and it is very troublesome to disassemble and transport the inspection; The field working conditions of the flowmeter are very different from the working conditions of the laboratory, and the deviation of the flowmeter accuracy cannot be determined. The use of portable ultrasonic flowmeter for on-line measurement of large-diameter flowmeters facilitates the metering work of water supply enterprises and effectively reduces the consumption of funds.