Admittance Point Level Switch

A static level sensor without any moving parts is called RF Admittance. Earth Extension (body), Compensation Shield, and Sensing Rod are its sensing components and together they provide three capacitances. Earth Capacitance, Sense Earth Capacitance, and Shield Sense Capacitance

Sensing Rod and Compensation Shield are both fed with a high frequency sine wave. No effective current flows between sense and shield because the voltage at the shield is identical to the voltage at the sense.

Shield-sense capacitance is eliminated from the measurement by using the same voltage or equip-potential drive to sense and shield. The circuit disregards shield-earth capacitance.

By doing so, the coating of the probe’s substance is eliminated.

Due to the shield’s electrostatic loading and subsequent selective sensitivity, the admittance device actually becomes reverse sensitive in the shield-earth zone.

Level cannot be sensed until a sufficient amount of material covers both the sense and the earth together because level is only detected by measuring sense-earth capacitance.