1. Change of situation conditions
The important reason is that the same period of the debugging period of the same section hinders the situation, but the source of the nuisance is not involved in the commissioning period but participates in the operation period. For example, an electromagnetic flowmeter that is not erected by a grounding shield is not operated by the factory during the commissioning period, and the instrument is operating normally. However, during the operation period, a new nuisance source (ratio than the pipe with a measuring point or a pipe welding at a remote location) is nuisance. The meter is running normally and the output signal is greatly bumpy.
2, the inner wall adhesion layer
Since the electromagnetic flowmeter measures the time of containing the suspended solid phase or the dirty body much more than other flow meters, the probability of the occurrence of the inner wall adhesion layer is relatively high. If the electrical conductivity of the adhesion layer is close to the liquid conductivity, the instrument can output the signal normally, but only transform the smooth area, forming a hidden obstacle to the measurement deviation; if the high conductivity adhesion layer, the electromotive force between the electrodes will be short-circuited; if the insulating adhesion layer The appearance of the electrode is insulated to disconnect the measuring circuit. The latter two signs will make the meter impossible.
3, lightning strikes
Lightning strikes feel transient high voltages and surge currents in the line, and entering the meter can damage the meter. There are three ways to introduce the lightning damage meter: the power line, the flow signal line between the sensor spoon converter and the excitation line. However, from the interpretation of lightning damage to the destruction of components, the high voltage and surge currents that are caused by the obstacles are introduced from the control room power supply line, and the other two ways are less. It was also learned from the scene of lightning strikes that not only the electromagnetic flowmeter was hindered, but also the other instruments in the control room were accompanied by lightning strikes. Therefore, the use of the unit should understand the importance of setting the lightning protection method for the power supply line of the control room. The current position has been discussed in the planning unit team and explored this topic.
As a highly sophisticated instrument, the flowmeter not only needs to strictly comply with its requirements during the manufacturing and use process, but also must pay special attention in the later maintenance to prevent the flowmeter from retiring early.