5 aspects of testing required to solve electromagnetic flowmeter failures

During the use of electromagnetic flowmeter, some faults will occur, which will affect the normal operation of the instrument. How to find the cause behind the fault is a very important task. We need to identify it through various types of detection methods. Under normal circumstances, our routine detection of electromagnetic flowmeter usually includes five aspects: electrode contact resistance, electrode polarization voltage, signal cable interference, and determination of ground potential and stray current flow direction in the pipeline. These five aspects can be carried out separately, but they are also interrelated. Changes in any one factor may cause changes in other factors. This reminds everyone to pay special attention to it during detection:
 
1. Electrode contact resistance measurement. The contact resistance value of the electrode and the liquid can indirectly estimate the general surface condition of the electrode and the lining layer without removing the flow sensor from the pipeline, which is helpful for analyzing the cause of the fault. Measuring the contact resistance value of the electrode and

the liquid can indirectly evaluate the general surface condition of the electrode and the lining layer without removing the flow sensor from the pipeline, which is helpful for analyzing the cause of the fault. It is especially convenient for the inspection of large-caliber electromagnetic flowmeters. This method can estimate the surface condition of the flow sensor measuring tube, such as whether there is a sediment layer on the electrode and the lining layer, whether the sediment layer is conductive or insulating, and the contamination condition of the electrode surface.
 
2. Polarization voltage of electrode Measuring the polarization voltage between electrode and liquid will help to determine whether the zero point instability or output shaking is caused by electrode contamination or covering. 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, otherwise it means that the electrode is contaminated or covered. The magnitude of the polarization voltage depends on the "electrode potential" of the electrode material and the properties of the liquid, and the measured value may be between a few mV and several hundred mV. Because the contamination of the two electrodes in actual operation cannot be completely 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. 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.
 
4. Determine whether there is ground potential. During normal use of electromagnetic flow juice, if the state of the electric (power) machine 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 terminal C and the protective ground terminal G can be short-circuited to determine whether there is ground potential by the change of zero point (or indication value).
 
5. Determine the direction of pipeline stray current flow. Sometimes, in order to find the source of pipeline stray interference, it is enough to be upstream or downstream of the flow sensor to narrow the search range and try to reduce or eliminate the influence of stray current interference.