STO wiring question

[dwoodlock]

Is the proper way to control a dual channel STO circuit for a servo or VFD with force guided relays which are actuated by the machine safety controller?

I understand generally how STO works, just trying to learn more about the safety circuitry.

Thanks

 

[joseph_e2]

I've done it through relays and with the safety outputs of the controller directly wired to the STO inputs of the drive. Generally, it depends on how many things I need to control with the same logic.

 

[Scottryan03]

It comes down to current required for your devices. A digital safety controller output is typically .5a, safety controller relay output closer to 6a, a safety rated control relay or contactor you can get 10-20a. I typically use the safety controller to power a safety control relay or contactor for my safety power.

Let me know if this helps. I can assist better with example schematics. My comm skills aren't always easy to understand.

 

[jholm90]

Check the STO current draw on all of the devices and compare to the output rating (just like all other output calcs)


If using interposing relays for the STO signals, be sure to add EDM monitoring to ensure they are not stuck on/bypassed and switching when commanded to.