Capacitance level detectors which are sometimes called as admittance level sensors. These sensors make use of radio frequency balanced impedance bridge circuit to find out whether the probe is in touch with the process material whose level is going to be detected. “Calibration is done when material is not in contact with the probe. The bridge is balanced by turning the adjustment pot to find the bridge balance threshold. When material comes in contact with the probe, the bridge becomes unbalanced and the comparing circuit realizes the change.”
RF level sensors usually work in the low radio frequency megahertz range and measure admittance i.e. conductance in an alternating current circuit which changes with level. Their sensitivity is measured in pico-farads i.e. pF.