Principle of Operation
Every substance has unique dielectric constant (dK). The sensor uses the difference in dK between material and air or vacuum to determine material presence.
Different types of oscillation and detection circuits as well as electrodes are available to suit a wide range of materials and process conditions.
Type R (parallel resonant circuit type)
A parallel resonant circuit is used, where a high frequency oscillation circuit and a synchronization (detection) circuit are separated. The detection circuit is synchronized with the oscillation frequency to create the largest high frequency voltage.
When the measured material reaches the detection circuit, synchronization is broken, decreasing high frequency voltage at the circuit.
This decreased voltage is rectified, and the decreased amount is dc amplified to give output signals.
Type S (series resonant circuit type)
Series resonant circuit is used. The circuit has a detection electrode as a part of the oscillation circuit. Change in the electrode capacitance (△C) renders the circuit to oscillate. The circuit starts oscillation and gives output signals when the material reaches the electrode.