Capacitive proximity sensors

Capacitive proximity sensors consist of an electrical resistor (R) and a capacitor (C) that together form an RC resonant circuit as well as an electronic circuit for evaluating the oscillation.

An electrostatic field is generated between the active electrode and the ground electrode of the capacitor. A stray field forms on the front side of the sensor. When an object is brought into this stray field, the capacitance of the capacitor changes (cf. Figure 4.5). The resonant circuit is attenuated and the downstream electronic unit actuates the output.

Capacitive proximity sensors not only respond to materials with a high electrical conductivity (e.g. metals), but also to all insulators with a high dielectric constant (e.g. plastics, glass, ceramic, liquids and wood).