Use of a DP (differential pressure) transmitter for level measurement


#1

A differential pressure transmitter gives a linear output for the differential pressure measured across its HP and LP chambers.
Connect the transmitter’s HP leg to the bottom of the tank and its LP leg to the top of the tank. The transmitter will read the liquid level accurately irrespective of the change in process pressure above the liquid surface.


#2

The transmitter will read the liquid level accurately

Not always true.

The transmitter will accurately report the hydrostatic head pressure, which is “interpreted” as level by correcting for the fluid’s density/Specific Gravity.

If the fluid’s density Specific Gravity used in the correction calculation is correct, then the reported level will be correct.

If the fluid’s density/Specific Gravity used in the correction calculation is incorrect, then the reported level will be incorrect.