Closed Tank- Wet Reference Leg:

Where the tank holds a condensable fluid, like as steam, a slightly variant arrangement is used. Within applications along with condensible fluids, condensation is greatly raised in the reference leg.  For compensate for this effect, the reference leg is filled along with the similar fluid as the tank. The liquid within the reference leg applies a hydrostatic head to the high pressure side of the transmitter, and the value of this level is constant as long as the reference leg is managed full. Some change within ?P is due to a change on the low pressure side of the transmitter if this pressure remains constant that was show in the figure.

Figure: Closed Tank, Wet Reference Leg

The filled reference leg applies a hydrostatic pressure to the high pressure side of the transmitter that is equal to the maximum level to be measured. The ?P transmitter is exposed to equal pressure on the high and low pressure sides while the liquid level is at its maximum; thus, the differential pressure is zero. Since the tank level goes down then the pressure applied to the low pressure side goes down also and the differential pressure increases. As a conclusion, the differential pressure and the transmitter outcome are inversely proportional to the tank level.