In the simplest terms, proximity sensors work by transmitting data about the presence or motion of an object into an electrical signal. They output an ON signal when the object enters their range. There are some key differences in the way that different proximity sensors work, as explained below:
Capacitive Proximity Sensor Working Principle
Capacitive proximity sensors work by detecting changes in capacitance between the sensor and an object. Factors such as distance and the size of the object will affect the amount of capacitance. The sensor simply detects any changes in capacity generated between the two.
Inductive Proximity Sensor Working Principle
Inductive sensors work by detecting eddy currents causing magnetic loss, generated by external magnetic fields on a conductive surface. The detection coil generates an AC magnetic field, and impedance changes are detected as a result of generated eddy currents.
Magnetic Proximity Switches Working Principle
Magnetic proximity switches are comparatively simple and straightforward. The reed end of the switch is operated by a magnet. When the reed switch is activated and ON, the sensor also turns ON.
It is also worth noting that proximity sensors are not affected by the surface colour of the object detected. They rely purely on physical movement and the motion of an object, so its colour does not play a role in the effectiveness of the sensor.