Measurement is made by applying an RF signal between the conductive probe and the vessel wall.
The RF signal results in a very low current flow through the dielectric process material in the tank from the probe to the vessel wall. When the level in the tank drops, the dielectric constant drops causing a drop in the capacitance reading and a minute drop in current flow.
This change is detected by the level switch's internal circuitry and translated into a change in the relay state of the level switch in case of point level detection.
In the case of continuous level detectors, the output is not a relay state, but a scaled analog signal.
Level Measurement can be divided into three categories: