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Why must electromagnetic flowmeter be grounded for field use?

Because the output signal of the electromagnetic flowmeter sensor is very small, usually only a few millivolts. In order to improve the anti-interference ability of the instrument, the zero potential in the input loop must be grounded, and the geodetic potential is zero potential, which is a sufficient condition for the sensor to be grounded. Poor grounding or no grounding line will lead to external interference signals, resulting in electromagnetic flowmeter AD converter sampling error, error in the form of: empty pipe, signal zero or negative signal.

The ground point of the sensor output signal should be electrically connected with the measured medium, which is a necessary condition for the operation of the electromagnetic flowmeter. If this condition is not met, the electromagnetic flowmeter cannot work normally, which is determined by the signal loop of the sensor. When the fluid cuts the magnetic field line to produce a flow signal, the fluid itself is zero potential, a positive potential is generated on one electrode, and a negative potential is generated on the other electrode, constantly changing. Therefore, the midpoint of the converter input (the signal cable shield) must be at zero potential with the fluid and be on, so as to form a symmetrical input loop. The midpoint of the input end of the converter is electrically connected with the measured current through the ground point of the output signal of the sensor.

For the connection problem with the earth with the telluric potential as the reference potential, because the general metal pipeline is connected with the earth, and the flowing medium is electrically connected with the earth through the metal pipeline, this point can generally be met.

Therefore, the electromagnetic flowmeter does not require a separate grounding device, especially a small caliber electromagnetic flow sensor, but a separate grounding device is conducive to the reliable operation of the instrument. In other words, there must be a correct understanding of the grounding problem of the electromagnetic flowmeter, which should be paid attention to, but it cannot be blindly overemphasized.


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