How does a proximity sensor work?

The Proximity Sensor is a sensor that detects the proximity of an object in the vicinity and is commonly used in industrial sites. As the name implies, as a sensor, it can output either 0 or 1 result.

Depending on the working principle, the proximity sensors can be divided into inductive and capacitive. In today’s article, we’re going to talk to you about how an inductive proximity sensor works.

Let’s get acquainted with what an inductive proximity switch looks like first.

Inductive proximity switch operates differently when in contact with ferrous and ferrous-free metals.
The inductive proximity switch generates a high-frequency magnetic field on its front surface through its internal oscillation circuit. The ferrous metal is easily magnetized when it is approached by a ferrous metal, and the process of magnetization absorbs the energy of a high-frequency magnetic field.

As the ferrous metal gets closer to the proximity sensor, the more the metal is magnetized, the more energy from the high-frequency magnetic field is absorbed. This causes the load on the oscillation circuit inside the

proximity switch to get bigger and bigger, and eventually, the oscillation circuit attenuates or stops.

The detection circuit inside the proximity sensor detects changes in the state of the oscillating circuit, thereby changing the output state and changing the signal value of the proximity switch from 0 to 1.

The waveform of the oscillating circuit before and after contact with the ferrous metal can be seen in the following figure.

When iron-free metals (e.g., aluminum, copper, etc.) are close to an inductive proximity switch, they do not absorb the energy of a high-frequency magnetic field. Conversely, such metals can also increase the frequency of the oscillation circuitry inside the proximity sensor. The internal detection circuit also detects this change, which changes the output state, changing the signal value of the proximity switch from 0 to 1.

The waveform of the oscillating circuit before and after contact with non-ferrous metals can be seen in the following diagram:

Totally, the working principle of inductive proximity switch is introduced here, let’s stay tuned!