Issues with measuring negative pressure using a differential pressure level gauge?
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How does the pressure measured under negative pressure change with the liquid level?
The pressure on the negative pressure side should not change with changes in liquid level; otherwise, how can the liquid level be determined?
As long as the pressure inside the container remains constant, the pressure on the negative pressure side also stays unchanged. I read an article a long time ago that stated differential pressure level gauges should not be used for negative pressures. Go back and look for it; if you find it, send it to you so you can study it
Fluctuations on the negative pressure side don’t matter, as what is measured is the differential pressure; changes in the pressure on the negative pressure side affect both the positive pressure chamber and the negative pressure chamber.
Do you mean that the pressure on the negative pressure side is the same regardless of the liquid level?
The differential pressure value is equal to the positive pressure minus the negative pressure; when the negative pressure changes, the differential pressure changes as well, so it shouldn’t matter
The pressure on the negative pressure side may change with the liquid level, but this does not affect the liquid level measurement by the differential pressure level gauge. The pressure measured on the negative pressure side is usually the gas pressure, which also acts on the positive pressure side; whereas the value that reflects the liquid level is the differential pressure, that is, the pressure on the positive pressure side minus the pressure on the negative pressure side.
The pressure on the negative pressure side remains constant and is equal to the pressure exerted on that side when the instrument is not in use, plus the internal pressure of the equipment. However, the internal pressure of the equipment has no effect on the liquid level, as the positive pressure side also experiences the same pressure, and these two pressures cancel each other out
When a differential pressure level gauge measures the liquid level, the pressure measured under negative pressure remains constant; generally, this negative pressure corresponds to one standard water column, which requires the transmitter to be adjusted for negative migration.