2TLC172083M0201, rev. A
9
www.jokabsafety.com
2011-09-16
System description / Application example
While the machine is running the movable guard is closed. The separate actuator is nested in the head of the
safety switch. In this state the safety outputs are closed and unlocking is disabled. In case of e.g. maintenance the
operator will need to gear into the machine behind the movable guard. In this case the operator will stop the
machine first. The safety switch will keep the actuator locked until the dangerous machine has come to a safe stop.
This can be achieved by using a suitable control device, such as a timer or lost motion detector. When the machine
is stopped, unlocking is enabled. An unlock command (power supplied or power cut off, depending on type), will
unlock the actuator and open the safety circuit. The safety relay will fall, and the machine cannot be started. The
movable guard can now be opened. Any of the forced disconnect contacts can be used in the safety circuit. Two
contacts are required for a dual-channel system. At least one of the contacts 31-32 or 41-42 should be used to
monitor the locking. The remaining two contacts can be used as auxiliary contacts signals or as a complement in
the safety circuit to the safety relay, to achieve certain functions.
The contacts for monitoring the position of the actuator are operated directly by the actuator in order to register the
position of the guard directly. The contacts for monitoring the locking function are directly connected with the
locking bolt. A failure of the locking function can be detected by the safety relay. The design of the locking is of
such a kind that the locking cannot be activated unless the actuator is completely inserted into the head of the
safety switch. Thus the contacts for monitoring the locking function can also be used to monitor the position of the
movable guard. The possibility to monitor both contacts (movable guard and locking function) separately leads to a
dual channel mode.
