For non-contact detection of non-metallic and metallic materials at ranges generally under 50mm (2 inches), capacitive sensors detect a change in capacitance caused by the approach of objects into their electrostatic field. Capacitive sensors find broad use in detecting plastic granules, liquids, bulk food products, or very small metal parts, and are used extensively in applications involving plastic injection molding, packaging, and liquid level detection.

Advantages of capacitive sensors include the ability to “tune out” non-metallic walls and barriers in order to detect liquids or bulk materials on the other side, and detection of very small metal parts that would be ignored by inductive proximity sensors.