Differential pressure level measurement technique makes use of a differential pressure transmitter which is installed at the bottom of the tank whose level is to be measured.
In case of open tanks, only high pressure ends of the DP transmitter is needed to be connected whereas the low pressure end of the DP transmitter is expelled into the atmosphere. Hence, the differential pressure happens to be the hydrostatic head or weight of the fluid contained in the tank.
The highest level detected by the differential pressure transmitter usually depends upon the maximum height of fluid above the transmitter, whereas the lowest level detected is based upon the position where the transmitter is attached to the tank or vessel.
The liquid inside the tank creates pressure which is comparatively higher than the reference atmospheric pressure and the DP Transmitter senses the head pressure developed by the height of the liquid in the tank. This is multiplied by a density variable to get the correct level measurement.
Note: The mmh20 and level values used in animation are only assumptions.
Also Read: Hydrostatic Level Animation