1 ã€No signal output from the flow sensor after power on
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Possible cause of failure and its treatment:
1) There is no flow of process media in the pipeline. Inform the process operator to open the valve.
2) The process medium in the pipeline flows but the flow rate is low. The wrong selection of the instrument causes the caliber to be too large and can only be changed.
3) If the process status is normal, the instrument may malfunction and the maintenance can be checked step by step. The vortex frequency detection element, ie, the probe, is currently a piezoelectric type. The insulation resistance of the probe is measured with a multimeter 200 Mf~ file, and it should be 10~IOOM~ at room temperature. Use a multimeter 2n file to measure the capacitance of the probe. When no load is used, the capacitance should be constant between 0.15 and 0.35nF. In the amplifier board circuit is set to detect signal 0, with the oscilloscope one by one to detect the waveform of each point, generally in the Schmitt trigger before the detection point, the signal waveform should be different amplitude sine wave, in Schmidt After the trigger signal waveform is a square wave.
4) Incorrect sensor supply. Check if the +12VDC or +24VDC sent to the sensor by the flow totalizer is normal.
5) If the instrument is normal after inspection, it indicates that the fault is in the secondary instrument and the secondary instrument can be checked for faults.
2. Possible cause of failure of signal output when there is no flow in the pipe and its handling method:
1 ) Large vibration of the pipe causes the sensor to output false signals. Find the source of vibration, eliminate pipeline vibrations or perform vibration reduction on the process piping.
2) Bad grounding, interference, and false signals. Check the grounding resistance, it should not be greater than 10Q, otherwise handle grounding.
3) The sensor gain is too large. Adjust the gain potentiometer to the proper value.
4) There is power frequency interference. Check the frequency of the signal output by the sensor. If it is 50Hz, it indicates that the flowmeter has a high-power motor or a relatively strong electric field. Take certain measures to reduce the interference or strengthen the shielding treatment of the signal line. 
3 , the sensor output signal is not stable at normal flow
1 ) There is no regular vibration in the pipeline. Find the source of vibration, eliminate pipeline vibrations or perform vibration reduction on the process piping.
2) The gain of the amplifier board is incorrect. Use an oscilloscope to check the waveform of the output signal. If there are multiple waveforms or waveforms, it indicates that the amplifier board is not working properly. The multiple waveforms indicate that the gain is too large, and the lost waveform indicates that the gain is too small. The gain of the amplifier board can be properly adjusted.
Steam flowmeter common fault inspection and treatment methods