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In electrical engineering, a limit switch is a switch 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 , as a safety interlock , or as a counter enumerating objects passing a point.
For example, elevators are equipped with an interlock that prevents the moving elevator from opening its doors and prevents the stationary elevator (with open doors) from moving. Interlocks may include sophisticated elements such as curtains of infrared beams , photodetectors , simple switches , and locks .
Tamper-resistant switches (or tamper-proof switches) are types of vandal-resistant switches which are not intended to be operated except by authorized users. They may control special functions, such as auditing of voting machines , operation of power tools or equipment, enabling of security alarm systems (e.g., arming and disarming), or ...
A stop switch to halt the elevator while in motion, which is often used to hold an elevator open while freight is loaded. Keeping an elevator stopped for too long may set off an alarm. Unless local codes require otherwise, this will most likely be a key switch. Some elevators may have one or more of the following:
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The hysteresis thresholds for switching (specified as B OP and B RP) categorize digital Hall ICs as either unipolar switches, [9] omnipolar switches, [10] or bipolar switches, [11] which may sometimes be called latches. [12] Unipolar (e.g., A3144) [13] refers to having switching thresholds in only one polarity of the magnetic field. Omnipolar ...
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The comb bearer, depending on what brand of the escalator will push back and/or up and activate limit switches in the event of an impact of something that jams through combs (typically stones, screws & popcorn) can be someone's shoe/item loose clothing.