Measuring the polarization voltage between the electrode and the liquid with the electromagnetic flowmeter will help determine whether the unstable zero point or output shaking fault is caused by the electrode being contaminated or covered.
Use the 2V DC range of a digital multimeter to measure the polarization voltage between the two electrodes and the ground (the electromagnetic flowmeter can be measured without power outage or without power outage). If the two measurement values are close to almost equal, it means that the electrode is not contaminated or covered, otherwise it means that the electrode is contaminated or covered. The size of the polarization voltage depends on the "electrode potential" of the electrode material and the properties of the liquid. The measured value may range from a few mV to hundreds of mV. Because in fact, the contamination conditions of the two electrodes during operation cannot be exactly the same and symmetrical, so the voltages on the two electrodes form an asymmetric common mode voltage.
The asymmetric common mode voltage becomes a differential mode signal, causing interference from the zero point offset signal cable. The signal cable is interfered by external electrostatic induction and electromagnetic induction, which will cause the zero point of the electromagnetic flowmeter to change. In order to determine whether the zero point change is due to the interference potential of the signal cable, it is necessary to determine the general scope of the interference and the degree of impact on the electromagnetic flowmeter. Measurement of electrode contact resistance: "The measured general resistance values RA and RR of the two electrodes, connected to the circuit as shown in Figures a and b respectively, and the measured zero point difference should be within 1% of the full scale value or within its basic error range.
The following points should be noted when measuring:
1. When connecting RA and RB, attention should be paid to not being affected by power interference, etc.;
2. The zero point of the converter may change slightly (usually increases) during measurement compared with the original connector measurement. It is generally considered that the change does not exceed about 5%;
3. Re- Connect the changed parts of the circuit, and keep the other circuits as they are;
4. When measuring, the environment around the sensor should be the same as when the fault occurs. It would be better if the nearby motor can be tested for power on and off.
Hangzhou Economic Development Area，Hangzhou 310018，China
