Safety Torque Off wiring with optocouplers

[Jeroen3]

You probably also want to comply with the relevant input levels defined in IEC 61131-2 instead of simply throwing an optocoupler in there "because everyone does that".
ST has some chips that can help with that.

[bookaboo]

How could that be done? Are you saying within the PCB footprint?
For context, the size of the PCB is at the moment 70mm diam, with a 15mm hole in the middle.

Best to keep the safety circuit outside your PCB, your PILZ PNOZ is likely a good idea, but it's outputs need to be used to reliably cut all the power to the hazard (i.e. not just issue a command to your controller, as that controller cannot be relied upon without it's own safety certification). In many applications you can use another relay or contactor, provided it's MTBF is high enough.

Safety certification is an engineering field in itself, your local compliance test house should be able to give you a free initial consultation (don't worry they charge plenty later ! )