Jemtech had an unusual technical requirement for a safety system that could determine whether the crane was inside or outside the safety zone. When inside the safety zone, special conditions had to be applied to the operation of the crane hoists.
Being a safety application, Jemtech approached the problem by using their VSY contactless safety switches.
The crane had to be detected as it passed the zone limit. The conventional solution meant fitting the key on the crane and the switch in a stationary position. This was not a safe solution if in the event the key was not detected, the crane could move in and out of the zone undetected.
In all safety switch applications, the switch had to be used so that it was closed except when the unsafe condition occurred. Jemtech decided to fix the key and the switch so that detection occurred all the time.
Failure of the switch or the key would result in detection of the crane as being in zone and therefore safe. By passing a metal flag between the key and switch to interrupt the sensor, electrically reliable mechanical and electronic detection was possible.
Jemtech moulded the key and switch parts into a single robust housing featuring a 100mm deep throat and a 30mm opening. This provided a large space for the metal flag to travel through and guarantee the positive breaking of the switch.
In the crane application, this meant that wheel wear that caused movement vertically and poor tracking laterally did not affect the reliability of the safety system.
A total of four switches were fitted to this application and have successfully enabled Jemtech to detect the position of the crane.
The new slotted safety switches are called VSSL safety switches and available from Jemtech.