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Safety Sensor: Use PNP Output Instead of NPN Output

FAQ No. FAQ02285

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Why does the Short-range Safety Light Curtain "F3SN/F3SH" employ the PNP output?


In the case when equipment is connected to a common earth ground (0V), the PNP output is used to prevent an output malfunction due to earth fault.

Therefore, Safety Sensors/ Safety Light Curtains designed for safe use employ the PNP output for ensuring the safety of customers.

Earth fault

* If the side of 24VDC is grounded, safety is ensured.

When using the NPN output, if a coating of output lines peels off and they are touching the frame of facilities, a hazardous source keeps existing and uncontrollable. It is very dangerous. Burnout of the coating and short circuit to the frame occur at an extremely high ratio.

Earth fault

If output lines are short-circuited, loads are stopped without running away because any voltage is not applied to them. It is very safe.


However, the system connected to 24VDC ground can also use equipment with NPN output, thus NPN output type models are also available for the F3SN-B Series.