Zero speed switch

Zero speed switches (ZSS) also known as Speed Actuating Sensing Switches^[1] are used to detect whether a rotating shaft is turning (even at very slow speeds) ^[2] in various machines, conveyors, power plants, and in industries involving the production of cement, sugar, textiles, paper, etc. Zero speed switches mainly use electromechanical, electronic, or magnetic proximity technologies. Electromechanical speed switches are direct coupled, speed-indicating devices which open or close a set of contacts mechanically, as a function of the rotational speed of the switch shaft. Electronic zero speed switches are direct-coupled, speed-indicating devices that open or close a set of contacts through a relay and electronic circuit. User-defined settings and the rotational input speed of the shaft determine the speed at which an electronic zero-speed switch trips.

A small timing delay may be required for avoiding nuisance tripping during running as well as during starting of the machine. This is taken care of in the electronics of the ZSS.