Rotary Gear type Crane Control Equipments make Limit Switches are used on Control / Power circuit of reversing drives so as to limit their rotation / movement within a predetermined position.
The function of the Limit Switch is to stop the mechanism of drive at the extreme clock wise / anti clock wise position. These Rotary Limit Switches are particularly suited for use on reversing drives such as Electric Hoists, Winches, Over Head Cranes, Traversers etc.
The contacts of these Limit Switches are rated for 40 amps at 500 Volts A.C.
The Limit Switch can be provided with 2NC contacts or (2No + 2NC) contacts as per the requirement.
The Geared type Rotary Limit Switch basically consists of heavy duty worm gear drive with a ratio of 48 :1 , 60 :1 or 96 :1
We also manufacture Rotary Limit Switches having Gear Ration of 1 : 50 1 : 200 and 1 : 500.
The Rotary Limit Switch is made in IP-41 as well as in IP-54 enclosure .
In case of IP 41 enclosure the housing is made from suitably reinforced sheet where as in case of IP-54, the cover is of cast Aluminum. Also the Base and cover have machined surface to protect the Limit Switch against dust.
The cam shaft which extends from behind the gear into the sheet steel housing accommodates the cams.
2 or 4 cams are used depending upon whether the Rotary Limit Switch is of 2 contacts or 4 contacts operation.
The contacts have a maximum continuous Current capacity of 40 amps AC.
The contact tips are made of high grade Silver Cadmium Oxide alloy.
When used for Series operation[ up to 40 Amps maximum], the Contacts are suitable for 720 operations per hour and in case of Shunt operation [ for Control Circuit ] , the Contacts are suitable for 1200 operation per hour.
The same Contacts can be used in Series as well as in Shunt configurations
The switching capacity of the Contacts when used for Shunt operation is 15 amps at 400 Volts, AC on highly inductive load and 2.5 amps at 220 Volts DC .
These switching capacities in fact are far in excess of what is actually required in practise and hence replacement of Contacts for Shunt may not be necessary for a long time.
The body of the Contacts is made of high grade Melamine which is specifically suited for heavy duty operation .The material is non – tracking and is capable of with standing heavy arcing.
The Rotary Limit Switch operates in the following manner :
The Mechanism or the Drive coupled to the Limit Switch actuates the Contacts through the Worm Gear Drive and the Cams.
When the Mechanism or the Drive approaches the pre determined position, the Cam strikes the Contact finger of the corrosponding Contact which in normal condition is in a closed position.This immediately opens the Contacts and the Circuit is broken there by disconnecting the respective Motor from the supply and resulting in the stoppage of the Drive or Mechanism.
The Actuator or Cam is provided with a maximum follow-through angle of 60 degrees there by ensuring that the normally closed Contact, which has been opened by the Actuator/ Cam shall remain in the open position for at least 7 full additional revolutions of the Input Shaft.
This provision is adequate for most of the Reversing Drives where the Mechanism or Drive comes to a complete stop with in 1/5th of a revolution of the Input Shaft of the limit Switch.