Capacitive proximity sensors are similar in size, shape, and concept to inductive proximity sensors. However, unlike inductive sensors, which use induced magnetic fields to sense objects, capacitive proximity sensors react to alterations in an electrostatic field. The probe behind the sensor face is a capacitor plate. When power is applied to the sensor, an electrostatic field is generated and reacts to changes in capacitance cause by the presence of a target. Capacitive proximity sensors are similar in size shape, and concept to inductive proximity sensors.
Capacitance is affected by the insulating characteristic of the target, or the dielectric constant.
The higher the dielectric constant, the more sensitive a capacitive sensor is to that target. For example, water and air are dielectric extremes. A capacitive proximity sensor would be very sensitive to water, with a dielectric constant of 80, which makes it ideal for applications such as liquid level sensing or product filling lines. The same sensor, however, would not be sensitive to air, with a dielectric constant of 1. Other target items would fall within the sensitivity range, such as wet wood, with a dielectric constant between 10 and 30, and dry wood, between two and six.