A proximity switch is a sensor that can detect when an object is approaching and is widely used in industrial settings. As its name suggests, it acts as a switch, outputting either a 0 or a 1.
Based on their different working principles, proximity switches can be divided into two types: inductive and photoelectric (mainly infrared). In this article, we'll discuss the working principle of inductive proximity switches.
Let's first take a look at what an inductive proximity switch looks like.
The working principle of inductive proximity switches differs when they contact ferrous metals and non-ferrous metals.
An inductive proximity switch generates a high-frequency magnetic field on its front surface through an internal oscillation circuit. When ferrous metal approaches it, the ferrous metal is easily magnetized, and the magnetization process absorbs the energy of the high-frequency magnetic field.
As ferrous metal approaches the proximity switch, the higher the degree of magnetization of the metal, the more energy of the high-frequency magnetic field is absorbed. This leads to an increasing load on the internal oscillation circuit of the proximity switch, eventually causing the oscillation circuit to decay or stop.
The detection circuit inside the proximity switch can detect changes in the state of the oscillation 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 ferrous metal can be seen in the following figure:
When non-ferrous metals (such as aluminum and copper) approach an inductive proximity switch, they do not absorb the energy of the high-frequency magnetic field. Instead, these metals can increase the frequency of the internal oscillation circuit of the proximity switch. The internal detection circuit can also detect this change, 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 a non-ferrous metal can be seen in the following diagram:
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