What Are Proximity Sensors ?

Proximity Sensors

A proximity sensor is a component which is designed to detect the absence or presence of an object without the need for physical contact. They are non-contact devices, highly useful for working with delicate or unstable objects which could be damaged by contact with other types of sensors.  This non-contact operation also means that most types of proximity sensor (excluding types such as magnetic proximity sensors) have a prolonged lifespan. This is because they have semiconductor outputs, meaning that no contacts are used for output. 

Proximity sensors are not affected by the surface color of the object detected. They rely purely on physical movement and the motion of an object, so its color does not play a role in the effectiveness of the sensor.

Proximity sensors are designed to provide a high-speed response (the interval between the point when the object triggers the sensor and the point when the output activates). Different types use varying sensing technologies, but they all have the same purpose. Different types of sensors are best suited to detecting different objects:

  • Capacitive proximity sensors – metals, liquids, water, resin, powders

  • Inductive proximity sensors – metals including aluminum, copper, brass, and iron

  • Magnetic proximity sensors – magnets

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 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 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.

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