|
Gravity Limit Switch. Gravity 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 Gravity type Crane Control Equipments make Limit Switch is to stop the mechanism of drive at the extreme top position of the snatch block in a Crane . The contacts of these Limit Switches are rated for 40 amps at 500 Volts A.C. The Limit Switch can be provided with 1NC contact or (1No + 1NC) contacts as per the requirement. Special configurations can also be supplied on request This limit switch is some what similar in construction to a Lever Limit Switch except for the Lever. In this case one side of the Lever has a weight and from the other side a plate is hung which eventually operates when the snatch block reaches its top position. The lever Limit switch operates in the following manner – When the Snatch Block of the Crane reaches its top position the Snatch Block pushes a Plate which is hanging from one end of the Lever of the Limit Switch. Due to the weight placed on the other end of the lever this lever is pushed up. When the lever is pushed up the shaft to which this lever is connected rotates there by rotating the cams which eventually open the contacts and disconnect the motor The Limit Switch contacts are automatically reset when the lever returns to zero position due to Gravitational force. The cam shaft on which the cams are fitted is mounted in the housing on moulded bushes of synthetic material which are fixed to the front and rear walls by means of screws.
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.
|
