Comparison of Safety: General Switches vs Non-contact Safety Switches

In Case of General Switches (e.g. Installed on a Door)

Machine door is open: Switch is OFF → Machine is stopped (Machine cannot be operated).
Machine door is closed: Switch is ON → Machine is running or ready to operate.
If the machine door is opened during its operation, the machine will stop.

(1) Safety cannot be ensured in the event of an emergency.	(2) The switch can be invalidated.
Overcurrent can cause loss of functions.	Fix actuator Put magnet intentionally on detecting unit
Very dangerous for workers because machine can be activated even when machine door is open.

(1) Safety cannot be ensured in the event of an emergency.

(2) The switch can be invalidated.

Overcurrent can cause loss of functions.

Fix actuator Put magnet
intentionally on detecting unit

Very dangerous for workers because machine can be activated

even when machine door is open.

In case of Non-contact Safety Switch “SS2 series”

Simplified Internal Diagram and its Operation

How Non-contact Safety Interlock Door Switches Work

The magnetic sensors in the decoding circuit detect polarities of multiple magnets in the transmitter unit.
Relays K1 and K2 make output only when the decoding circuit detects a specific combination of polarities.
The anomaly detecting circuit monitors whether any failure (single failure) has occurred in the controlling circuit 1. & 2. and the decoding circuit when the machine door is opened.
When a failure occurs in either controlling circuit, the anomaly detecting circuit will communicate the failure to the other controlling circuit, so that any output will not be made thereafter to the relay that is not experiencing a fault.

*Anomaly mentioned here means that one of the relays does not turn OFF due to its internal failure.