Electromagnetic flowmeter in the use of some problems, affecting the appearance of the normal operation, such as the back of the fault to find out the factors is a very important operation, we need to through a variety of different types of inspection methods to identify, under general conditions, we about the electromagnetic flowmeter routine inspection, generally including electrode touch resistance, electrode polarization voltage There are five aspects of signal cable disturbance, determination of grounding potential and stray current flow direction of pipeline. These five aspects can be carried out separately and are also related to each other. Any change of any element may lead to changes of other vendors. This suggests that we should pay special attention to this when checking:
1、 Electrode touch resistance measurement, electrode and liquid touch resistance value, can directly estimate the general situation of the electrode and lining layer without removing the flow sensor from the pipeline, which is helpful to analyze the fault factors.
Measuring the contact resistance of electrode and liquid can directly evaluate the general condition of electrode and lining layer without removing the flow sensor from the pipeline, which is helpful to analyze the fault factors. Especially, it brings great convenience to the inspection of large-diameter electromagnetic flowmeter. This method can be used to evaluate the internal and external surface conditions of the flow sensor measuring tube, such as whether there is a stacking layer between the electrode and the lining layer, whether the accumulation layer is conductive or insulating, and the surface pollution of the electrode.
2、 The measurement of the polarization voltage between the electrode and the liquid will help to determine whether the electrode is polluted or covered up. The polarization voltage between the two electrodes and the ground is measured by using a digital multimeter with 2V dc gear (the electromagnetic flowmeter can be used to measure the voltage without power failure or power failure). If the two measurements are close to each other, the electrode is not contaminated or covered, otherwise the electrode is contaminated or covered. The polarization voltage depends on the “electrode potential” of the electrode material and the properties of the liquid, and the measured value may be in the range of several MV to several hundred MV. Because it is impossible for the two electrodes to be completely and symmetrically polluted during operation, the voltage on the two electrodes forms an asymmetric common mode voltage. The asymmetric common mode voltage becomes a differential mode signal, resulting in a zero offset.
3、 Measurement of signal cable disturbance signal cable will change the zero point of electromagnetic flowmeter due to interference of external electrostatic induction and electromagnetic induction. In order to judge whether the zero point change is due to the disturbance potential of signal cable, it is necessary to determine the general scale of disturbance and the influence degree on electromagnetic flowmeter.
4、 In the normal use process, if the state of the electric (Mechanical) machine adjacent to the sensor changes (such as leakage), the grounding potential will change and lead to the change of zero point. To check whether there is such influence, short circuit the converter operation grounding terminal C with the maintenance grounding g terminal, and judge whether there is grounding potential by changing the zero point (or the indicated value).
5、 The stray current flow direction of the pipeline is sometimes found to be the source of disturbance in the upstream of the flow sensor and the downstream flow, so as to reduce the search scale and try to reduce or eliminate the disturbance effect of stray current.
Editor in charge: WV