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Old September 18th, 2023, 10:50 AM   #1
lanczos
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Safety PLCs

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?

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Old September 18th, 2023, 11:03 AM   #2
mk42
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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.
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Old September 18th, 2023, 11:08 AM   #3
Steve Bailey
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That's a feature of every PLC I've ever dealt with, not limited to safety PLCs.
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Old September 18th, 2023, 12:15 PM   #4
lanczos
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Thanks, figured as much, just wanted to confirm.
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