This level measurement works on the principal of dielectric constant. Dielectric Constant of process fluids like Oils, Water Solutions etc are different from that of the Air. Dielectric constant of Air is almost 1.0.
Capacitance level sensor measures the changing capacitance between two plates, separated by process fluid.
As the fluid level rises, capacitance rises proportionally. An electric circuit called Capacitance Bridge measures the total capacitance and provides a continuous level measurement.
There are two configurations of such level transmitters :
- Capacitance is measured between process fluid and insulated rod attached to the transmitter.
- Capacitance is measure between tank metal wall or reference probe and un-insulated rod attached to the transmitter.
Check out these youtube videos to better understand it.