Working Principle of Capacitance Continuous Level Transmitter?

The probe forms a capacitance with the metalic tank-wall.
The capacitance is sum of three capacitance:- C(air)=ε(air) x P x (H-L) C(material)=ε(material) x P x L C(residual) is due to device itself.
Where ε(air) is the dielectric constant of air ≈1. ε(material) is dielectric constant of material. P is the constant of probe and installation, H is the active length of probe and L is the level of material
Capacitance to level translation is performed with the aid of on-site calibration also called “wet-calibration”.

The device stores a low level capacitance as level for 4mA and high level capacitance as level for 20mA as defined by the user.