Proximity switches are devices that can open or close an electrical circuit when they come within a certain distance of another object. There are a number of possible functions for proximity switches, including uses in industrial equipment, security systems and robots.
For instance, a machine designed to grip objects in an assembly line could be fitted with a proximity sensor that would make the machine's gripping arm stop contracting once it makes contact with an object. Otherwise, the machine could crush the object. Another interesting application for a proximity switch is for steering self-driving robots.
There are several different types of proximity switches. Inductive proximity switches, also known as magnetic proximity switches, operate similarly to metal detectors. By generating a magnetic field, inductive proximity switches can detect when they are a certain distance from a metallic object. The drawback to this design is that they can only interact with metal objects.
Capacitive proximity switches are another type of proximity switch. This version functions by detecting changes in capacitance. Basically, it constantly transmits radio waves on a certain frequency. The frequency naturally changes when the switch gets close to another object. The downside is that these proximity switches are more responsive to objects that conduct electricity than those that do not.
A third form of proximity switch is called an infrared proximity switch. These switches send out invisible beams of infrared light, and then detect any reflections of the light to determine if another object is nearby. These devices are fitted with modulators that control the frequency of the light they project and receive, which reduces the chances of background light affecting the sensor. More advanced types of infrared proximity switches can even measure the distance to a nearby object.
The final type of proximity switch is an acoustic proximity switch. These switches essentially use echolocation to determine their proximity to other objects; this is similar to how bats navigate, or how sonar technology works. Sub-sonic sound waves are projected from the switch, and then it measures the time it takes for those sound waves to bounce back. This lets the proximity switch know how close it is to nearby objects.