How bubbler type level transmitter works in close tank?
It works on the principle of measurement of back pressure exerted on the HP side due to the rise in level in the tank. It can work on both close and open tank bubbler type can be used for open or close tank level measurement. Lp side measure back press and hp side measures pressure inside the top tank
A closed tank always requires a differential pressure transmitter for hydrostatic head pressure level measurement, whereas an open-to-the-atmosphere tank can use a gauge pressure transmitter for level measurement.
There must be some vent/relief valve on the tank/vessel that will prevent excessive pressure from the constant addition of the air/gas from the bubbler.
The DP transmitter high side connects to the bubbler dip tube and measures the combined hydrostatic head pressure of the liquid column and the pressure in the vapor space above the liquid.
The DP transmitter low side connects to the vapor space above the liquid.
The DP transmitter subtracts the low side from the high side and reports the differential pressure, in this case, the hydrostatic head pressure of the liquid column represented by the back pressure in the bubbler dip tube.