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Standardized limit switches are industrial control components manufactured with a variety of operator types, including lever, roller plunger, and whisker type. Limit switches may be directly mechanically operated by the motion of the operating lever. A
electrical engineering
Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electronics, and electromagnetism. It emerged as an identifiable occupation in the l ...
, a limit switch is a switch
In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
operated by the motion of a machine part or the presence of an object. A limit switch can be used for controlling machinery as part of a control system
A control system manages, commands, directs, or regulates the behavior of other devices or systems using control loops. It can range from a single home heating controller using a thermostat controlling a domestic boiler to large industrial ...
, as a safety interlock, or as a counter enumerating objects passing a point.Stephen Herman, ''Industrial Motor Control'' Cengage Learning, 2009 chapter 11 "Limit Switches"
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, 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".
Standardized limit switches are industrial control components manufactured with a variety of operator types, including lever, roller plunger, and whisker type. Limit switches may be directly mechanically operated by the motion of the operating lever. A reed switch
Reed or Reeds may refer to:
Science, technology, biology, and medicine
* Reed bird (disambiguation)
* Reed pen, writing implement in use since ancient times
* Reed (plant), one of several tall, grass-like wetland plants of the order Poales
* ...
may be used to indicate proximity of a magnet mounted on some moving part. Proximity switches operate by the disturbance of an electromagnetic field, by capacitance, or by sensing a magnetic field.
Rarely, a final operating device such as a lamp or solenoid valve is directly controlled by the contacts of an industrial limit switch, but more typically the limit switch is wired through a control relay
A relay
Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts
An automotive-style miniature relay with the dust cover taken off
A relay is an electrically operated switch ...
, a motor contactor
:''In semiconductor testing, contactors can also be referred to as the specialized socket that connects the device under test.''
:''In process industries, a contactor is a vessel where two streams interact, for example, air and liquid. See Gas ...
control circuit, or as an input to a programmable logic controller
A programmable logic controller (PLC) or programmable controller is an industrial computer that has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, machines, robotic devices, or any activity t ...
.
Examples
Miniature snap-action switches are components of devices likephotocopier
A photocopier (also called copier or copy machine, and formerly Xerox machine, the generic trademark) is a machine that makes copies of documents and other visual images onto paper or plastic film quickly and cheaply. Most modern photocopier ...
s, computer printers
In computing, a printer is a peripheral machine which makes a persistent representation of graphics or text, usually on paper. While most output is human-readable, bar code printers are an example of an expanded use for printers. Diff ...
, convertible
A convertible or cabriolet () is a passenger car that can be driven with or without a roof in place. The methods of retracting and storing the roof vary among eras and manufacturers.
A convertible car's design allows an open-air driving expe ...
tops or microwave oven
A microwave oven (commonly referred to as a microwave) is an electric oven that heats and cooks food by exposing it to electromagnetic radiation in the microwave frequency range. This induces polar molecules in the food to rotate and produce ...
s to ensure internal components are in the correct position for operation and to prevent operation when access doors are opened. A set of adjustable limit switches installed on a garage door opener
A garage door opener is a motorized device that opens and closes a garage door controlled by switches on the garage wall. Most also include a handheld radio remote control carried by the owner, which can be used to open and close the door from a ...
shut off the motor when the door has reached the fully raised or fully lowered position. A numerical control
Numerical control (also computer numerical control, and commonly called CNC) is the automated control of machining tools (such as drills, lathes, mills, grinders, routers and 3D printers) by means of a computer. A CNC machine processes ...
machine such as a lathe has limit switches to identify maximum limits for machine parts or to provide a known reference point for incremental motions.
References
Safety switches Sensors {{Engineering-stub