Differential Capacitance Type Proximity Sensor Precautions During Use

Go back to the list of "all products"

[1] Principle of Differential Capacitance Proximity Sensor

The differential capacitance type proximity sensor is a sensor that detects the difference (⊿ C) between a reference capacitance (Cref) inside the sensor and the capacitance (Cx) at the sensor detection surface.
Since it detects changes in lines of electric force coming from the detection surface, it is a sensor that can output minute capacitance changes as an analog voltage.

[2] Two motion models

【Grounding model】

A person or a detected object with a large surface area has a large capacitive coupling and is equivalent as if it is grounded to earth, GND.
When a finger or the like approaches the detection surface, electric lines of force occurring between the electrodes are attracted to the finger and so the lines of electric force between the electrodes are reduced.
As a result, capacitance (Cx) decreases.

【Floating model】

When the capacitive coupling with ground is small, as the dielectric approaches a position between the electrodes, the capacitance increases with the magnitude of the dielectric constant (ε).

[3] Noise control

Because differential capacitance type proximity sensors detect changes in weak electric fields (electric field lines), be sure to connect the sensor power supply GND (0 V) directly or via a capacitor of 0.1 μF or more to the metal chassis so that it is at the same electric potential.

◆How to check the noise voltage

• Set the tester to its AC voltage range
• If the output voltage is 10 mVrms or less, it is no problem