What are Capacitive Sensors?
Capacitive proximity sensors function so that any material - even non-metallic materials - in the proximity of the active surface (sensing area) will produce oscillations that lead to a change of state. Unlike an inductive proximity sensor that oscillates until the target it present, a capacitive proximity sensor oscillates when the target it present.
Capacitive sensors contain an oscillator transistor in the front section. The R-C (resistor-capacitator) oscillating circuit is influenced by variations in capacity when any material - solid or liquid (water, wood, metals, coffee, powders, etc...) - comes into contact with the active surface of the sensor. Capacitive proximity sensors use the variation of capacitance between the sensor and the object being detected. When the object is at a pre-set distance from the sensitive side of the sensor, an electronic circuit inside the sensor begins to oscillate. The rise or the fall of such oscillation is identified by a threshold circuit that drives an amplifier for the operation of an external load. A screw placed on the backside of the sensor allows regulation of the operating distance.
AECO Capacitive Proximity Sensors Catalog