Introduction
A capacitive sensor is a proximity sensor that detects a change in capacitance when a surface comes near the sensing element. It can detect almost all solid and liquid materials.
How it works
- the sensing element is a capacitor, made of a sensitive electrode and a reference electrode with a dielectric between them
- the capacitor is part of an oscillator circuit
- the circuit oscillates only when the capacitance is more than a set threshold value
- the start of oscillation is changed into an output voltage, which shows that an object is present
Limitation
The sensitivity decreases quickly after a few millimetres. The response also depends on the material of the object.