What Are Proximity Switches?
A "switch" is a device that opens or closes an electrical circuit. In your home, a light switch mounted on the wall turns the flow of electricity on or off to a lighting fixture. Proximity switches are designed to open or close circuits under specific conditions, such as when a person approaches a door, and a motor can then be turned on to open the door (such as automatic door openings at supermarkets).
Applications
Typical uses for proximity switches include machine tool safety, the detection of moving objects (to open a door or turn on security lights) and material handling, and in manufacturing applications there are endless tasks for proximity switches, from counting bottles on an assembly line to checking component positioning.
Specific Types
Proximity switches are used to detect the "proximity" or presence of an object. Because there are different types of objects in different environments, there are unique types of proximity switches, each designed to sense a particular item. The environment they will be used in is also a consideration. In an industrial application, proximity switches may need to work in harsh environments, such as extreme dust or noise. There are switches designed to operate in such hostile areas.
Optical Proximity Switches
Using infrared technology, optical proximity switches are set to only be sensitive to infrared light, and so can be used in environments where there is noise, light and even radiation. For example, in an assembly line situation where a switch needs to close every time a shiny metal can passes by a certain point, an infrared beam of light can be aimed at the area where the cans will pass by, and an infrared proximity switch can detect the light as it is reflected off the cans. However, since there is visible light in the plant, this could interfere with proper operation of the proximity detector if it were not for its ability to screen out visible light and only be sensitive to infrared.
Magnetic Proximity Switches
As its name implies, magnetic proximity switches detect the presence of a magnetic field. A magnet attached to a cam shaft, for example, can trip a magnetic switch every time it passes by the switch.
Ultrasonic Proximity Switches
Typically, a transmitter device sends out a modulated ultrasonic signal (a wave whose frequency is above the range of human hearing). If that signal is reflected by an object, the switch senses the presence of that object.
Inductive Proximity Switches
Inductive proximity switches detect the presence of metallic objects. These must be objects made of electrically conductive metal.
Capacitive Proximity Switches
These switches can be designed to detect the presence of nonmetallic objects, such as plastic parts, glass bottles, bulk materials and metals that are not electrically conductive.
Tags: detect presence, switches designed, assembly line, electrically conductive, every time, only sensitive, only sensitive infrared
