Electromagnetic Flow Meter After-Sales Case 5

Field problem

A sewage treatment plant in Hefei, Anhui Province, China: the data displayed by DN600 electromagnetic flowmeter is shaking, and the same phenomenon still appears after restarting the pump.

Troubleshooting and analysis

After receiving customer feedback, the technical team of ARTang immediately went to the customer site to check and analyze the faults:

The electromagnetic flowmeter was tested by engineer ARTang on the spot, and it was found that the electromagnetic flowmeter was stable at around 800 m³. Use multimeter to check whether the resistance value of electromagnetic flowmeter is normal. When the pump is restarted again, the flow rate fluctuates in the range of 800-2400 m3. Then, ARTang engineer started the other three pumps and found that the flowmeter was stable at 2400m3. It is determined that the fluctuation is caused by air bubbles in the pipe.

Solution

Install an exhaust valve in the pipe to completely exhaust bubbles.

Customer feedback

After installing the exhaust valve, the output data of the electromagnetic flowmeter header is stable and runs well.

What if there are bubbles in the pipe?

1. If the bubbles in the measured pipeline are caused by the improper installation position of the electromagnetic flowmeter, for example, if the electromagnetic flowmeter is installed at the high point of the pipeline (height > 5 m), residual gas or air sucked by the outside will cause the screen to jump, the measurement error caused by the bubble problem can be solved by changing the installation position of the electromagnetic flowmeter, for example, installing the electromagnetic flowmeter at the lowest point of the pipeline or installing an instrument on the U-shaped pipe.

2. If the diameter of the electromagnetic flowmeter is large or it is inconvenient to change the installation position of the electromagnetic flowmeter, a collection valve and an exhaust valve can be installed upstream of the electromagnetic flowmeter; According to professional research, large-diameter electromagnetic flowmeter will show signal jump due to bubble problem, and the jump range is 20%-50%. After installing the exhaust valve and collection bag, the measurement can basically return to normal.