Details
RF Admittance is a static level sensor with no moving parts. Its sensing parts are:-
1) Earth Extension (body)
2) Compensation Shield
3) Sensing Rod
…which form three capacitances:-
1) Shield Earth Capacitance
2) Shield Sense Capacitance
3) Sense Earth Capacitance
A Sine wave of high frequency is fed into both Sensing Rod as well as Compensation Shield. Voltage at shield is equal to voltage at sense, no effective current flows between sense and shield.
This same voltage or equi-potential drive to sense and shield removes shield-sense capacitance from the
measurement. Shield-earth capacitance is ignored by circuit.
This removes the effect of material coating on probe.
Which makes the probe selectively sensitive and by virtue of electrostatic loading of shield, it actually makes admittance device reverse sensitive in the shield-earth region.
Since, level is detected by measuring sense-earth capacitance only, level is not sensed until sufficient amount of material covers sense & earth combined.
