Principle of Operation

The basic oscillator circuit is of the parallel resonance circuit with L (coil) and C (capacitance between the electrodes).

The oscillation frequency (f) of this circuit is : f = 1/2 π √LC.

The frequency without material around the sensor (f1) is: f1 = 1/2 π √LC, where C is the capacitance without material around the sensor (zero point).

With material around the sensor, the capacitance increases (C+ΔC), and the frequency (f2) is: f2 = 1/2 π √L(C+ΔC), where C+ΔC is the capacitance with material around the sensor (span point).

The sensor detects the frequency change from f1 to f2, and gives a current output (4 to 20mA). The integrated microcomputer makes it possible to offset the output value and switching output for zero and span points.