An electrical switch is any device used to interrupt the flow of electronics in a circuit. They are essentially binary devices, meaning they are either completely on/closed or completely off/open. The simplest switches are those in which two electrical conductors are brought in contact with each other by the motion of an actuating mechanism. Other are more complex, containing electronic circuits that are able to turn on or off depending on some form of physical stimulus. In this blog, we will discuss some of the most common types of switches.
Toggle switches are actuated by a lever in one of two or more positions. A common example of a toggle switch is the household light switch. Most toggle switches will come to rest in any of their lever positions, while others have an internal spring mechanism that returns the lever to a normal position, allowing for momentary operation.
A joystick switch is actuated by a lever that moves in more than one axis of motion. One or more of many switch contact mechanisms are actuated based on which way the lever is pushed or how far it is pushed. Some joystick switches are specifically designed to be operated by the motion of a machine arm rather than by a human operator. These motion operated switches are known as limit switches.
Limit switches closely resemble rugged toggle or selector hand switches affixed with a lever pushed by the machine part. The levers are often tipped with a small roller bearing, preventing the lever from being worn off by repeated contact with the machine part.
Proximity switches sense the approach of a metallic machine part either by a magnetic or high-frequency electromagnetic field. Basic proximity switches utilize a permanent magnet to actuate a sealed switch mechanism when the machine part gets close. More complex proximity switches operate similarly to a metal detector, energizing a coil of wire with a high-frequency current and electronically monitoring the magnitude of said current. If a metallic part gets close enough to the coil, the current will increase and trip the monitoring circuit.
Another type of proximity switch is the optical switch, which consists of a light source and photocell. Machine position is detected by the interruption or reflection of a light beam. Optical switches are useful in safety applications, where beams of light can detect when personnel enter into a dangerous area.
In many industrial processes, switches are used to monitor various physical quantities. These are known as process switches and can be used to sound alarms or shut down processes or equipment if their operation is potentially dangerous or destructive. There are many types of process switches, the most common being speed switches, pressure switches, and temperature switches.
These sense the rotary speed of a shaft either by a centrifugal weight mechanism mounted on the shaft, or by a non-contact detection method such as optical or magnetic.
Gas or liquid pressure is commonly used to actuate a switch mechanism if that pressure is applied to a piston, diaphragm, or bellows, which converts pressure to mechanical force.
Finally, temperature switches feature a thin strip of two metals back-to-back, each one having a different rate of thermal expansion. When the strip heats or cools, the differing rates of thermal expansion causes the strip to bend. The bending of the strip can then be used to actuate a switch contact mechanism.
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