Electrical capacitance sensors detect and measure capacitance, which is the ability to store an electrical charge. Capacitive sensors are essentially oscillators with open an capacitor that generates an electrostatic field. If there is no object nearby, the oscillator does not oscillate, and the electrical capacitance sensor remains quiet. But as an object to be detected comes closer, capacitance increases, and oscillation begins. As the oscillation increases, it is detected by a circuit that, in turn, generates an output signal that indicates the proximity of the object.
Electrical capacitive sensors can be used to perform high speed, non-contact detection of a wide variety of materials – including cardboard, paper, plastic, and metals -- at distances up to 10 mm. The output of electrical capacitance sensors can be used to drive other equipment to perform tasks such a counting items on an assembly line. Electrical capacitive sensors can also be used to detect fluids in non-metallic containers. Through careful adjustment (they are maximally effective at low switching frequencies), electrical capacitive sensors can perform reliably in a wide variety of applications and offer extremely long life.
Because dissimilar materials influence the electrostatic field differently, the capacitive sensors must be tuned during installation in order to achieve optimum effectiveness. For example, capacitance level sensors used to detect fluid levels through the wall of a glass (using capacitance glass sensors) or plastic tank must be adjusted to “null out” the influence of the tank wall, and this adjustment will change, depending whether the tank is made of glass or different types of plastic. Once adjusted, however, electrical capacitive sensors usually provide extremely reliable operation and long life in relatively clean environments.