Inelectrical engineering, alimit switch is aswitch 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 acontrol system, as a safetyinterlock, or as a counter enumerating objects passing a point.[1]
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. Areed switch 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 orsolenoid valve is directly controlled by the contacts of an industrial limit switch, but more typically the limit switch is wired through a controlrelay, a motorcontactor control circuit, or as an input to aprogrammable logic controller.Fail-Safe Wiring: In safety-critical applications, such as end-of-travel stops for industrial actuators or CNC machines, limit switches are typically wired in aNormally Closed (NC) configuration. This creates a fail-safe architecture: if a wire breaks or a connector becomes unplugged, the circuit opens and the machine controller interprets the signal as the limit being reached, causing an immediate stop. Conversely, if a switch were wired Normally Open (NO), a broken wire would result in the signal never changing, potentially allowing the machine to drive through its physical hard stops and cause catastrophic mechanical failure.
Miniature snap-action switches are components of devices likephotocopiers,computer printers,convertible tops ormicrowave ovens 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 agarage door opener shut off the motor when the door has reached the fully raised or fully lowered position. Anumerical control 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.
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