Working principle of rotary limit switch

A rotary limit switch works on the principle of a worm drive . A worm drive mechanism is suited so that enough torque is generated to move the attached gears within the limit switch .
the shaft of the limit switch has threads which are matches and attached to a helical gear.

As the shaft rotates , the gear rotates according to the gear ratio. The gears are attached to a cam mechanism which rotate along with the central gear, a rotary limit switch has a minimum of two cams , one for setting the upper limit of the hoist machinery and one for setting the lower limit of the hoist machinery .

Screws are provided for each cam .Each cam can be adjusted according to user requirements to fine tune the upper and lower limit these cams operate the contacts within the limit switch.

After the cam adjustment is done according to the user , as soon as the hoist machinery reaches the upper vertical limit, the cams operate the contacts which stop the moving machinery . The contacts can be of normal closed (NC) or normally open (NO) type. Once any limit is reached by the EOT crane , the crane will only be able to move in the opposite direction thus preventing an accident.