We build small deburring cells. The next one has two E-stops, one guard door with a tongue interlock, one PowerFlex 525 on the spindle and a pneumatic clamp. Standard PLC is a CompactLogix 5069-L306ER, nothing exotic.
Our usual panel shop quoted a 440R dual channel relay and two 100S contactors, a few hundred. The integrator the customer uses says put a Compact GuardLogix in, 5069-L306ERS2, "future proof", and quoted about ten times that.
I've priced both and read the ISO 13849 summary twice, and I still can't say what actually decides it. The customer's risk assessment says PLr d for the door and the E-stops.
Is PL d only reachable with a safety PLC? That's what the integrator implied. I don't believe it, but I can't argue it, am I missing something obvious?
What does the risk assessment say has to happen for each one? Door open and E-stop pressed, same response, spindle off and clamp released? Or different? That's the question, not the brand of the box. I've seen the same cell done three ways on three platforms and all three passed.
Same response for all three. Drop the contactors, STO on the 525, clamp goes to the safe state. No zones, no muting, nothing runs while the door is open.
Sorry, so PLr is what the risk assessment says you need, and PL is what the circuit you built actually reaches, I think? So a relay could reach d?
Right, finn, that is the difference. And yes it can.
olly, for what you've described: both E-stops and the door in series, two channels, into one dual channel relay with monitored reset. Relay outputs open two C09-class contactors with mirror contacts in the feedback loop, and both STO inputs on the PF525. That's Category 3, and with decent parts it reaches PL d without trying. Easy to validate too, a screwdriver and a stopwatch.
A safety PLC earns its money when there are zones, muting, safe speed, or more than a handful of functions that change over time. One door and two stops isn't that. The risk assessment decides, not the budget and not the quote. Someone did a decent article on the PL side of it: https://plctr.com/introduction-to-functional-safety-in-plc-programming/
One thing I'd add. If the customer ever wants the door and the E-stops to do different things, say door stops the spindle but holds the clamp, that's two functions and two relays. By the third relay a small safety controller starts to be cheaper and easier to change, I reckon. Still not "future proof", just arithmetic.
Went relay. 440R-D22R2, both E-stops and the door on the two channels, monitored reset, two 100S-C09 in series with the NC mirrors in the loop, and both STO terminals on the 525 off the relay outputs. Customer's safety person did the SISTEMA on it, PL d, and signed the RA against it.
What I had wrong the whole time was thinking the PL came out of the box you buy. It comes out of the architecture and the parts in it.
Kai's point is the one that will bite me. If the customer ever wants the clamp to hold with the door open I'll be back. Thanks ronh55, kaim and finn.
Ok, so the box doesn't set the PL. Got it.