Why does an electromagnetic flowmeter show a negative value when the pipeline is empty or not fully filled?
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Electromagnetic flowmeters detect empty pipes or pipes that are not fully filled, with gas present. At this time, the flow meter will display a negative value or the flow rate will fluctuate greatly. Why is a negative value displayed? Could some expert explain the principle behind this?
If a stone is thrown into a river, can you describe the shape of the splashes it creates?
Negative values are generally displayed this way by the manufacturer; sometimes, if the flow direction is reversed, negative values will also be shown.
A negative value indicates the presence of backflow signal; backflow occurs, and when there is gas present in the electrode area, the flow meter may sometimes show no flow reading. Gas-containing fluids cannot be measured by electromagnetic flow meters, as these meters require the pipe to be completely filled with liquid.
The appearance of a negative value usually indicates that the electromotive force detected by the electrode is negative, of course, this is under the condition that the flow rate is correct.
It was wrong from the start! Is it still meaningful to show what? It can no longer perform normal sensing and calculations internally! It doesn’t matter what is displayed! Can you trust it even if it shows the correct value?
Knowing it’s wrong, I just want to understand the specific reasons for this situation. I can understand values fluctuating, but negative values are something I don’t quite get. After all, I’m new to this field and there are many things I still don’t understand
There’s no particular reason; it’s possible for it to randomly jump to any value, and it just happened that this one jumped to a negative value.