A basic inductive proximity sensor detects metal objects through the principle of electromagnetic induction. It consists of a coil of wire and an oscillator circuit. Here's a step-by-step explanation of how it works:
Oscillator Circuit: The sensor contains an oscillator circuit that generates a high-frequency alternating current (AC) signal. This oscillator circuit is responsible for producing an electromagnetic field around the coil.
Electromagnetic Field Generation: When the oscillator circuit is activated, the coil of wire generates an electromagnetic field around itself. This field radiates outward from the sensor's active surface.
Metal Object Detection: When a metal object comes within the range of this electromagnetic field, it induces eddy currents within the metal due to electromagnetic induction. Eddy currents are circular currents that flow within the metal as a response to the changing magnetic field.
Changes in Inductance: The presence of these eddy currents within the metal object causes changes in the inductance of the sensor's coil. Inductance is a property of an electrical circuit that represents its ability to store energy in a magnetic field. The proximity of a conductive metal object alters the inductance of the coil.
Oscillator Frequency Change: The changes in inductance affect the frequency of the oscillator circuit. As the inductance changes due to the presence of the metal object, the frequency of the AC signal generated by the oscillator circuit also changes.
Detection and Output: The sensor's circuitry monitors the frequency of the oscillator and compares it to a reference frequency. If the frequency deviates beyond a certain threshold, it indicates the presence of a metal object within the sensor's detection range. This change in frequency is then converted into a digital signal, typically an on/off state, which is used as the output to indicate the presence or absence of the metal object.
Adjustable Sensing Distance: The distance at which the sensor can detect metal objects is called the sensing distance. This distance can be adjusted by changing the properties of the sensor's coil, the frequency of the oscillator circuit, or the sensitivity settings of the sensor.
It's important to note that inductive proximity sensors are specifically designed to detect conductive metal objects. They are not effective at detecting non-metallic objects or materials with low electrical conductivity. These sensors find applications in industrial automation, manufacturing, robotics, and various other fields where non-contact metal detection is required.