Hi,
I've seen this on many machines over the years. Usually on the main control panel there are two buttons, one for control power on and one for control power off.
I have also seen these called "master on/off"
I have seen these perform various functions. Is there any standard on what these are supposed to do? I have seen them drop out certain contactors etc. Just wondering if there is any standard for this.
you can add this to the "standard" of anecdotal uses.
But typically the systems we design or make will have a safety circuit that cuts out the common power to outputs along with tripping safety relays.
The safety relays would be tied to all the doors, guards, e-stops, etc. cutting a safety relay would have all things tied to it, including locking guards that won't unlock to allow entry until X time has passed (internal safety relay time delay type). and then any contactors powered by the safety relay to cut off any possible motor movement.
the big one is the control power, so the output power would be cut by the safety relay as well. We leave the power to the PLC and inputs on, so you will still see output lights, and inputs working, and the PLC won't be faulted. you can still get feedback, but nothing can be physically powered by the PLC because the power would run through the safety relays. This was a big deal on a lot of machines that required human interaction to do setups, remove bad parts, etc, from machine that had 20-30 air cylinders that needed to stay retracted, but also shouldn't fire and come down while someone is working. The issue always arose that they could have a faulty valve, or be manually activated, so a HVLP air system was added so that when estops were hit, or doors opened. the guns would have a high enough pressure to hold in place, but too low of a pressure to allow them to transition easily or damage someone if they did get activated somehow.
As far as a standard..... it's always changing, Osha and NFPA are always updating based on new incidents happening. Standards are always changing as new ways to do safety are developed or improved on also. I don't know if there is a dead set standard other than the ones written in the Osha and NFPA guarding/safety standard, just because every process is different and requires a different way to maintaining safety.