Zero Elevation in Level Measurements of closed vessels (tanks) - Wet Leg

Wet leg method:

Similarly, a d/p transmitter is connected to the closed tank: the low pressure tap is the pressure of the gas above the liquid in the upper part of the tank.

A relatively heavy liquid (high density) that does not easily evaporate to fill the tube. The pressure of the gas in the tank is then applied to the pressure detector through this liquid.

Liquid-level measurement: Closed tank –- Wet Leg

The following relationship exists:

High pressure tap pressure, PH =ρ1g (H+h1)+PG

Low pressure tap pressure, PL= ρ2gh2 +PG

Pressure differential, PH-PL= ρ1g (H+h1)- ρ2gh2

ρ2=density of the liquid in the wet leg, (kg/m3)
h2=the height of the liquid in the wet leg, (m) .