Operation and design of capacitive sensors

The capacitive sensor basically functions like an open capacitor. An electrical field is formed between the measuring electrode and the GND electrode. If a material with a dielectric constant εr greater than air enters the electrical field,  the capacity of the field increases depending on the εr of this material. The electronics measure this capacity increase, the generated signal is conditioned during subsequent signal processing and causes output switching at a corresponding magnitude.

Sensors with GND electrode

These sensors can be flush-mounted with the sensing face in a material. Because the measuring field of these sensors extends from the measuring to the integrated GND electrode, a defined measuring field is created. They are particularly suitable for detecting non-conductive materials such as oils, glass, wood or plastics, but can also detect conductive materials just as well. To prevent undesired switching and moisture on the sensor surface, a compensating electrode was integrated to suppress undesired objects.

Sensors without GND electrode

Generally these sensors cannot be flush mounted. Since they do not have a GND electrode, the object to be detected performs the function of a GND electrode. Sensors without a GND electrode feature low sensitivity to soiling and condensation and are suitable especially for level tasks. To achieve long sensing distances, the medium to be detected should be conductive and optimally grounded.