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Proximity switches are switches that are capable of opening or closing an electrical circuit when they come in contact with or come within a certain distance of an object. Hence, Proximity switches are most commonly used in manufacturing equipment, robotics, and security systems. There are four basic types of proximity switches: infrared, acoustic, capacitive, and inductive.
Infrared proximity switches
The working of Infrared proximity switches is based on use of invisible infrared light beams. When infrared proximity switches sends out beams of invisible infrared light. A photodetector on the proximity switch detects any reflections of this light. These reflections allow infrared proximity switches to determine whether there is an object nearby. However, proximity switches with just a light source and photodiode are susceptible to false readings due to background light. Hence to avoid this, more complex switches modulate the transmitted light at a specific frequency and have receivers which only respond to that frequency. Even more complex proximity sensors are able to use the light reflected from an object to compute its distance from the sensor.
Acoustic proximity sensors
The working of Acoustic proximity sensors is based on use of sound instead of invisible infrared light These sensors use a transducer to transmit inaudible sound waves at various frequencies in a preset sequence. After sending sound waves, they measure the length of time the sound takes to hit a nearby object and return to a second transducer on the switch. To be precise, acoustic proximity sensors measure the time taken by sound waves to hit the target and come back (similar to the sonar devices), or the time it takes for sound pulses to "echo".
Capacity proximity switches
The working of capacity proximity sensors is based on detection of change in capacitance around targeted source. Generally, a radio-frequency oscillator is connected to a metal plate. When the plate moves closer to an object, the radio frequency changes, and the frequency detector sends a signal telling the switch to open or close.
Downside
These proximity switches have the disadvantage of being more sensitive to objects that conduct electricity than to objects that do not.
Inductive proximity switches
The working of Inductive proximity switches is based on magnetic fields. In fact, the working of inductive proximity switches are similar in principle to metal detectors. Inductive proximity switches detects distant objects by generating magnetic fields and measuring changes around the targeted object. A coil of wire is charged with electrical current, and an electronic circuit measures this current. If a metallic part gets close enough to the coil, there change in the current (i.e., there is an increase in the current) and the proximity switch opens or closes accordingly.
Downside
The main disadvantage of inductive proximity switches is that they can only detect metallic objects.
Applications
Manufacturing processes: To measure the position of machine components.
Security systems: For detecting the opening of a door
Robotics: They can used to monitor a robot or its components` nearness to objects and steer it accordingly.
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