limit switch is a switch operated by the motion of a machine part or presence of an object. They are used for controlling machinery as part of a control system, as a safety interlocks, or to count objects passing a point. A limit switch is an electromechanical device that consists of an actuator mechanically linked to a set of contacts. When an object comes into contact with the actuator, the device operates the contacts to make or break an electrical connection.
Limit switches are used in a variety of applications and environments because of their ruggedness, ease of installation, and reliability of operation. They can determine the presence or absence, passing, positioning, and end of travel of an object. They were first used to define the limit of travel of an object; hence the name “Limit Switch”.
In most cases, a limit switch begins operating when a moving machine or a moving component of a machine makes contact with an actuator or operating lever that activates the switch. The limit switch then regulates the electrical circuit that controls the machine and its moving parts. These switches can be used as pilot devices for magnetic starter control circuits, allowing them to start, stop, slow down, or accelerate the functions of an electric motor. Limit switches can be installed into machinery as control instruments for standard operations or as emergency devices to prevent machinery malfunction. Most switches are either maintained contact or momentary contact models.
- Windmill Switches: Another slightly more complicated example would be a windmill limit switch which allows it to operate in two different directions and have multiple positions and switches.
- Rotary Gear Limit Switch: If you would like the motor to stop after a set number of shaft rotations, a rotary gear limit switch can be used. The shaft on the switch is attached to a motor (usually indirectly via sprockets or gears) so the limit switch shaft turns as the motor turns. Inside the switch are gears, and a series of cams.
- Reed Switches: Reed switches detect the presence of magnetic fields and can be used to indicate proximity to a magnet. So you can mount a magnet to a device and use a reed switch to detect when the magnet reaches a set position.
- Proximity Switches: Proximity switches use a magnetic field and detect disruptions in that field usually caused by the presence of metal to indicate when a piece of metal is in the desired position.
- Gold-silver alloy
- Platinum-gold-silver alloy
- Silver-palladium alloy
- Silver-nickel alloy
- Silver-indium-tin alloy
- The designs are generally simple and straightforward
- They work well in almost any industrial setting
- They exhibit high accuracy and repeatability
- They are low power consumption devices
- They can switch high-inductance loads
- They can be used to switch multiple loads
- They are simple to install
- They are rugged and reliable
- They typically have heavy-duty electrical contacts meaning they can be used to switch higher levels of current directly without the need to utilize secondary relay control
Source : Wikipedia, Springercontrols, Thomasnet
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