Capacitive Sensors – Part I

Written by: Bjoern Schaefer

In this new series we will write about different aspects of capacitive sensors in today’s factory automation world. Capacitive sensors found their place in certain industries and applications as effective problem solvers for specific tasks such as plastic pellet detection devices in injection molding machines and liquid level monitors in the semiconductor industry.

In the first part, I would like to give you a brief introduction to this extraordinary sensing technology. Probably the most amazing aspect, is the fact that capacitive sensors can be found in such an incredible diverse spectrum of applications.

Pressure – the capacitive sensor measures the spacing to the diaphragm which provides a signal linear to the pressure level.

Liquid level – capacitive liquid level sensors can detect liquids by direct immersion into the tank or through non-metallic walls by measuring the change of capacitance between two conductive electrodes.

Displacement – capacitive displacement sensor can measure spacing between conductive objects down to resolutions of 10-9 mm.

Thickness measurement – with a known and constant dielectric, capacitive sensors can be used to measure the thickness of non-metallic objects.

Presence detection – capacitive proximity switches detect non-metallic objects for rather short distances disregarding color or texture of the target.

Material composition – in oil refineries, capacitive sensors detect the relative amount of water in oil.

Touch-pad – a 2-dimensional capacitive sensor matrix provides exact position feedback through glass or plastic surfaces.

Humidity – a change in humidity causes a change of the dielectric constant of air.

Certainly each area of application provides it own challenges to the sensor design and functionality, but the important point here is to show the obvious adaptability and robustness of capacitive sensing technology in general.

In the next part we will look at the underlying physical basics and challenges of capacitive sensors.


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