Five key points for special testing of electromagnetic flowmeter

Nowadays, electromagnetic flowmeters have been widely used, but in order to make better use of them, we cannot ignore their detection. The following article will talk about several special tests about them.

1. Electrode contact resistance. Measuring the liquid contact resistance value of the electrode spoon can indirectly evaluate the general surface condition of the electrode and lining layer without removing the flow sensor from the pipeline, which is helpful for analyzing the cause of the fault.

2. Electrode polarization voltage. Measuring the polarization voltage between the electrode and the liquid will help to determine whether the zero point instability or output shaking is caused by electrode contamination or coverage. Use the 2V DC range of the digital multimeter to measure the polarization voltage between the two electrodes and the ground respectively (the electromagnetic flowmeter can be measured without power off or with power off). If the two measured values ​​are almost equal, it means that the electrode is not contaminated or covered. The size of the polarization voltage is determined by the "electrode potential" of the electrode material and the properties of the liquid. The measured value may be between a few mV and several hundred mV. Because the pollution of the two electrodes in actual operation cannot be exactly the same and symmetrical, the voltage on the two electrodes forms an asymmetric common mode voltage. The asymmetric common mode voltage becomes a differential mode signal, causing zero point offset.

3. Determine the direction of stray current in the pipeline. Sometimes, in order to find the source of interference from pipeline stray current upstream or downstream of the flow sensor, the search range can be narrowed to try to reduce or eliminate the interference from stray current.

4. Determination of signal cable interference. 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 affected by the interference potential of the signal cable, it is necessary to determine the general range of the interference and the degree of influence on the electromagnetic flowmeter.

5. Determine whether there is a ground potential. During the normal use of the electromagnetic flow juice, if the state of the motor (force) near the sensor changes (such as leakage), the ground potential will change and cause the zero point to change. To check whether there is such an impact, the converter working ground C terminal and the protective ground terminal can be short-circuited to determine whether there is a ground potential by the change of the zero point (or indication value).