After the split electromagnetic flowmeter has been initially debugged and operated normally for a period of time, failures may occur during operation.
Common causes of failure include: adhesion layer on the inner wall of the flow sensor, lightning strikes, and changes in environmental conditions.
1. Changes in environmental conditions
The main reasons are the same as the failure environment during the debugging period in the previous section, except that the interference source does not appear during the debugging period but intervenes again during the operation period. For example, an electromagnetic flowmeter with unsatisfactory grounding protection. During the commissioning period, the instrument operates normally because there are no factory interference sources. However, during the operation period, new interference sources (such as pipes near the measurement point or pipe welding at a distance) appear. The instrument operates normally, but the output signal fluctuates significantly.
2. Inner wall adhesion layer
Since the electromagnetic flowmeter has far more opportunities to measure suspended solids or dirt than other flow meters, the probability of failure caused by the inner wall adhesion layer is also high. It's relatively high. If the conductivity of the attached layer is similar to the conductivity of the liquid, the instrument can still output signals normally, but the flow area will change, causing a hidden obstacle to measurement deviation; if there is a high conductivity attached layer, the electromotive force between the electrodes will be short-circuited; if there is an insulating attached layer , the electrode surface is insulated and the measurement circuit is disconnected. The latter two phenomena will make the instrument unable to work.
3. Lightning strike
Lightning shock will cause instantaneous high voltage and surge current in the line, and if it enters the instrument, it will destroy the instrument. There are three ways to introduce lightning-damaged instruments: power lines, flow signal lines and excitation lines between sensors and converters. However, analysis of components damaged by lightning faults shows that most of the induced high voltage and surge current that cause the fault are introduced from the power supply line in the control room, and the other two paths are less common. It was also learned from the scene of the lightning strike accident that not only the electromagnetic flowmeter malfunctioned, but also other instrumentation circuits in the control room often experienced lightning strike accidents at the same time. Therefore, the user unit must understand the importance of setting up lightning protection measures for the power lines of the control room instruments.
Hangzhou Economic Development Area，Hangzhou 310018，China
