Physical Science - Other

How a Proximity Switch Works



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You may not know the term “proximity switch” but you have seen them in action; you may use them when you golf, fish or hunt, and you may have even sworn at them from time to time. A proximity switch will either open or close an electrical or magnetic circuit when something comes within a certain distance of it. Think of some of the new gadgets in mini-vans, like back-up assist and object detection, which are based on proximity switches and proximity sensors. The proximity switch tells when an object is within an approximate distance (range finders, fish finders, metal detectors, etc.), or when the sensor comes within the proximity of an object (object detection in vehicles, smile detection in cameras, etc.).

A proximity switch is an electromechanical device that emits a beam of light to oncoming objects, and when the beam of light (or a laser beam, radio wave or magnetic field) reaches back to the switch it reverses its position. If the switch was open when the beam is emitted, it will become closed when that beam is redirected back at it by a solid object, like a car, motorcycle, boat, etc. They can also be used to find differences in mass, which is used for mineral detection and other related fields.

Proximity switches are used in red-light cameras and roadside speed-trap boxes, fish finders and depth finders on fishing boats, in metal detectors and portable distance finders like they use for golfing as well as hunting. A sniper’s range finder uses a proximity switch to find the exact distance between the rifle and the target. Sensors for wind speed, altitude and temperature can be incorporated into the circuit, which the proximity switch activates or deactivates once predefined parameters have been met.

There are three main types of proximity switches, and each is defined by the way in which they detect the distance between two objects; photoelectric proximity switches use light, inductive proximity switches use radio waves and magnetic proximity switches use magnetic fields. When a field’s strength or voltage is changed it opens a proximity switch which completes the circuit, which can then be used to translate the distance between two objects. The object that the beam reflects off of can either be a solid object or a field. The solid object can be something like a car going through a red light, which would cause the proximity switch to engage the red-light camera`s shutter. When the reflection used is a field, like the magnetic field between two magnets or a magnet and a conductive field, like a non-porous rock, the differences between two objects can be detected, like how metal detectors work.

A proximity switch needs to have proximity sensors in order to function properly. The proximity sensor is the object that detects the returning beam of light or the returning laser beam or the lessening/growing of a magnetic field, and then it sends a return signal to the proximity switch to close or open the circuit, depending upon the initial stage of the circuit (if it was open when the signal is sent from the sensor to the switch, the circuit will close, and vice- versa).

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  • InfoBoxCallToAction ActionArrowhttp://sensors-actuators-info.blogspot.com/2009/08/proximity-sensor.html