Safety PLCs

[lanczos]

Do all of the so-called "Safety PLCs" have a software-generated watchdog or heartbeat, so that if the software locks-up, crashes, or enters an infinite loop (for whatever reason), a hardware layer will detect the loss of the heartbeat and move all outputs to a safe state? Is that a standard feature?

Thanks!

 

[mk42]

For every safety system that I've used, it's there somewhere, yes. Otherwise it wouldn't be very safe.


In Siemens systems, the outputs themselves are "smart" and do the heartbeat detection as part of the internal diagnostics. If they find a fault in themselves, or if they lose comms to the PLC, then they go to the predefined safe state.

 

[Steve Bailey]

That's a feature of every PLC I've ever dealt with, not limited to safety PLCs.

 

[lanczos]

Thanks, figured as much, just wanted to confirm.