Part time at a small shop while I'm at school, they have a shrink wrapper from 2009 with a Micro820 and a PowerFlex 4M on the film roller. The E-stop on the front is a red mushroom into input _IO_EM_DI_05, which everyone here just calls DI05. Rung is basically:
XIC _IO_EM_DI_05 OTE Run_Seq
Press the E-stop and the sequence stops, but if the roller was running it keeps running at speed until someone hits Stop on the little panel.
I tried adding XIO _IO_EM_DI_05 into the drive start rung and an OTE to the stop output, and now the roller stops when you hit the button. But it took a program change to make the E-stop stop the motor, and that feels wrong, I think.
Sorry if this is basic, first real machine. Is that it, or what am I missing?
Which contactor drops when you hit that button? Any? Or does the E-stop only go into the PLC input and nowhere else? Look at the panel, not the program. And is there a safety relay anywhere in there, a little yellow one.
only the PLC. There's one contactor in front of the drive but it's pulled in by a Micro820 output when the machine is switched on. No yellow relay anywhere. So the button doesn't touch anything but DI05.
Then you don't have an E-stop, you have a stop button painted red. That was common on small shop machines in 2009, if I remember right it was cheap and nobody asked. Doesn't make it right. If the PLC stalls, the output card fails on, or the drive holds speed on a comm fault, that button does nothing.
Keep your rung change, it's a good process stop. It is not the E-stop, and no rung ever will be. Same on a Micro820, a Siemens, a CODESYS box.
An E-stop is a safety function. It removes power on its own, with nothing in the standard program in the way. Here: both contact blocks on the mushroom into a dual channel safety relay, monitored reset, relay outputs open the contactor coil, mirror contact in the feedback loop. The 4M has no STO, so the contactor is the only thing that stops the roller. The PLC gets a relay aux as a status input. What PL it needs comes from the risk assessment, which the shop owner has to get done. There's a writeup on the interlock side here: https://plctr.com/implementing-plc-safety-interlock-systems-in-industrial-environments/
So the rung stays on DI05, but it's not the E-stop, the relay is. And the comm loss setting on the drive doesn't matter for this because the relay drops the contactor whatever the drive thinks?
Right. Comm loss is a drive question. The E-stop has to work with the drive on fire.
Shop owner got an electrician in this week. 440R dual channel relay, both NC blocks on the mushroom, contactor coil through the relay outputs, mirror contact in the feedback loop, reset button next to it. Micro820 now reads a relay aux as _IO_EM_DI_05 and my rung is the process stop. Electrician tested it with the PLC unplugged, roller drops.
Turns out the red button only ever went into a standard input, which is why only the program reacted to it. The relay and the contactor stop the roller now, and my rung is the sequence stop it always was.
Still odd to me that it sat like that from 2009 and nobody asked. Thanks louk and kaim.
Retitled for search, the old title was "E-stop weirdness".