In brief
A capacitive sensor detects objects and fill levels without contact by evaluating the change in an electric field between its electrodes.
Contents
What is Capacitive sensor?
With its active face, a capacitive sensor forms an open capacitor. When an object enters the stray field, the capacitance changes because the material has a different dielectric constant from air. As a result, it detects not only metal but also plastic, glass, wood, powder, granules and liquids. Common applications are level detection on tanks, hoppers or silos and presence detection of non-metallic parts.
Key ratings are sensing distance, housing style, mounting type, output type (PNP, NPN, normally closed, normally open), supply voltage, degree of protection and temperature range. On many units, sensitivity can be adjusted by potentiometer or teach-in. The actual sensing distance depends heavily on the material; substances with a low dielectric constant are only detected at a shorter distance. For liquids, there are designs with media-resistant housings that are screwed directly into a vessel.
False switching is often caused by build-up, moisture or condensation on the sensor face and by sensitivity that has not been readjusted. After a replacement, the setting usually has to be made again. Modern units partly compensate for slight build-up themselves, but they do not replace regular cleaning of the active face.
In practice: maintenance and procurement
In addition to the manufacturer part number, housing style, output type and voltage, it should be stated which medium is detected and whether the sensor measures through a vessel wall. Note the sensitivity setting so that the replacement unit can be adjusted again quickly.
Synonyms and abbreviations: capacitive proximity switch · capacitive proximity sensor · capacitive level sensor · proximity sensor
Frequently asked questions
Which materials does a capacitive sensor detect?
Capacitive sensors detect almost all substances whose dielectric constant differs from that of air, i.e. metals, plastics, glass, wood, paper, bulk materials and liquids. The higher the dielectric constant, the greater the achievable sensing distance. Water-based media are therefore usually detected more reliably than dry plastic granules.
Can a capacitive sensor measure through a vessel wall?
Yes, if the wall is made of a non-conductive material such as plastic or glass and is not too thick. The sensor then detects the medium behind the wall, for example for level detection. The sensitivity must be set so that the wall itself is not detected as an object.
What information is needed for a replacement capacitive sensor?
The manufacturer part number, housing style and size, sensing distance, mounting type, output type, normally closed or normally open function, supply voltage, connector type, degree of protection and temperature range are needed. It is also helpful to state the medium being detected and whether the sensor comes into contact with the product, for example in food applications.