Introduction

Gravity limit switch works on the basic principle of weight balance scale where One counter weight is mounted at one side of the lever and another suspended weight is tied at another end of the lever.

Working principle of Gravity limit switch

At the center of the lever a Shaft is present with attached Coaxial cams .The lever shaft and cams , all rotate simultaneously at the same angle.

These cams are responsible for changing the state of electrical contacts position, placed inside the limit switch enclosure. Electrical Output wire is fed to crane control panel.

The suspended weight is directly connected to the hoist wire rope (as shown in Above Animation ) at the predetermined point where it prevents the hoist from reaching the upper block and rope drum.

Suspended weight is a little heavier than the counter weight ,so due to gravity effect suspended weight wire become stiff and it makes counter weight lift upward.During normal operation the limit switch normally remains closed.A gravity limit Switch will not have a spring return mechanism .

Gravity limit switch operates when the hoist reaches its predetermined point. In this condition the suspended weight rests on the surface of the hoist and suspended weight wire sags and counter weight changes the position and electrical contactor cut off power to stop the hoist motor.

Gravity limit switches can be used parallelly with rotary limit switch in a vertical type motion such as hoisting .

If the rotary limit switch fails to activate at the correct number of turns, the gravity limit switch will be operated to provide an emergency stop .