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Problem: Analog Input 4-20mA from Electromagnetic Flowmeter Sensor

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I am using DVP-ES2 PLC with DVP04AD-E2. I connected the flowmeter to the analog input module (4-20mA). And I noticed something weird, when the flowmeter shows 4mA value (no water flow at all) the data in the PLC keeps coming like 20-30 (0-32000). And when I change to the other port of the analog input , it even reaches value like 100 although there is no water flow at all. Note: I have done proper scaling to Liter/second and do proper grounding. Do you know what is the cause of this?

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Posted (edited)

Noise.

Almost every flowmeter has a setting called something like Low flow cutoff.   It is a signal level at which any flow below that level is reported as zero flow, primarily to cover this circumstance.  Find the low flow cutoff, figure out what units it uses, (% of span, counts, engineering units) and put in a number slightly higher than your existing low flow values.

As a side note, unless the flow meter has a tight shutoff valve on both ends, there can be actual flow even though the pump is not running.  Bleed level flows happen as the sytem equilibrates after the pump turns off and gravity works on the remaining liquid in the pipes, sometimes even siphoning flow.

Edited by DanW

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