What is detection principle of capacitive proximity sensors


Can anyone please explain me the detection principle of capacitive proximity sensors in layman terms? I tried to read various online articles but didn’t get much.

Looking to receive some useful advise.


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Hi @electronerd224,

What online sources have you already gone through, and which part of the online resource left you with doubts?

To understand how a capacitive sensor works, you must first understand how a capacitor is constructed and works. This I believe you can look up online.

For the capacitive proximity sensor, detects objects in its detection range, as these objects change the dielectric medium through which the electric fields from the capacitor pass. This causes the charge capturing capacity of the capacitor to change. This change can be detected by continuously charging and discharging the capacitor through a constant value resistor, and measuring how fast or how slow the capacitor charges or discharges.

As with any type of proximity sensor, the detection distance of the capacitive sensor also changes based on the material which it is detecting.

Capacitive Proximity Sensors detect changes in the capacitance between the sensing object and the Sensor. The changes in the capacity generated between these two poles are detected. The objects that can be detected depend on their dielectric constant, but they include resin water in addition to metals.

The capacitive proximity sensor consist a high-frequency oscillator along with a sensing surface formed by two metal electrodes. When an object comes near the sensing surface, it enters the electrostatic field of the electrodes and changes the capacitance of the oscillator.
As a result, the oscillator circuit starts oscillating and changes the output state of the sensor when it reaches certain amplitude. As the object moves away from the sensor, the oscillator’s amplitude decreases, switching the sensor back to its initial state.

The capacitive proximity sensors uses the variance in the capacitance of the sensor to conclude that an object has been detected. The mechanism for this category is quite simple in which the sensor act as a separate plate of the capacitor and the object acts as another plate or voltage source for the object. The air is the dielectric material between these two potentials. As soon as the object enters the dielectric of the plates, the capacitance of the capacitor changes. This change is taken as detection of object.

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Hi @vinayak,

Thank you for the response!

I recently visited this one https://www.derf.com/an-overview-on-proximity-sensors/ where I got the information about construction and working of proximity sensors but they have not mentioned about the detection principle. So I thought to ask here. I’m sure there must be a range(Sense to some distance) of sensors as well, correct?

Thanks for answering.

Yes, correct. I understood now. Thanks so much!