Electromagnetic flowmeter zero check and adjustment

In providing electromagnetic flowmeter technical services to users, it is often encountered that after users purchase the electromagnetic flowmeter and use it for a period of time, they find that the measurement data is inaccurate when they use it again.

In fact, this is not a quality problem with the electromagnetic flowmeter itself. Because the user did not follow the after-use care and maintenance methods in the instruction manual.

1. Regularly check the electrical performance of the sensor during electromagnetic flowmeter maintenance:

First, roughly measure the resistance between the electrodes. Disconnect the signal connection between the sensor and the converter. The sensor is filled with liquid. Use a multimeter to measure the resistance value of the two electrodes and the ground terminal to see if it is within the value range specified by the manufacturer, and the two measured values ​​are roughly the same.

Record the resistance value measured for the first time. This value will be useful for later determining the cause of sensor failure (such as whether the deposition layer is conductive or insulating).

Secondly, drain the liquid out of the sensor, wipe the inner wall, and after it is completely dry, use a megger to measure the resistance between the two electrodes and the ground terminal.

Finally, check the insulation resistance of the excitation coil, remove the sensor excitation coil, connect the terminals to the converter, and measure the insulation resistance of the coil with a megohmmeter

2. Electromagnetic flowmeter Maintenance zero point inspection and adjustment:

Before the electromagnetic flowmeter is put into operation, the zero point must be adjusted when the electromagnetic flow sensor is filled with liquid and is stationary after being powered on. After being put into operation, the flow should also be stopped regularly for zero checks based on the operating conditions; especially for sedimentation, easy-to-contaminate electrodes, and non-cleaning fluids containing solid phases, more inspections should be carried out in the early stages of operation to gain experience and determine the normal inspection cycle. The electromagnetic flowmeter with AC excitation method is more likely to produce zero point drift than the rectangular wave shock ratio, so more attention should be paid to inspection and adjustment.

Give two examples of application errors that caused failure of the deposition layer. One is that in oil drilling and cementing projects, the total flow volume of cement slurry is an important process parameter, and high-pressure electromagnetic flowmeters are often used. The instrument is used intermittently. After use, rinse the sensor measuring tube with clean water and leave it empty the rest of the time. Due to incomplete cleaning, the residual cement slurry on the inner wall of the measuring tube solidified into a thin layer. In the past two months, it accumulated to form an insulating layer, covering the entire electrode surface, resulting in abnormal operation and eventually failure to work.