Safety PLC - PLC Programming & Automation Forum

PROFIsafe F-DI passivates with F-monitoring time exceeded since the MRP ring went in

tomhw — Sat, 19 Sep 2026 15:05:09 +0000

TIA V17, CPU 1515F-2 PN, six ET 200SP stations with F-DI and F-DQ modules, all PROFIsafe. We shipped the machine last year on a line topology.

The customer had their switches changed to Scalance XC208 and asked me to configure MRP, which I did on a site visit. Since then the far station on the ring passivates two or three times a day. Their buffer says "F-monitoring time exceeded" on the F-DI, then it reintegrates after an acknowledge.

I tried swapping the IM 155-6 PN HF on that station with a spare, same thing. The customer wants MRP taken out again, "it worked before".

The F-monitoring time is whatever TIA proposed, 100 ms I think, and I never changed it. I'll own that. Fourteen devices in the ring.

Is it the ring, or the monitoring time itself, any thoughts?

Panel shop used a standard red 22mm pushbutton as the E-stop, auditor flagged it

fee_m — Sat, 19 Sep 2026 14:58:03 +0000

Apprentice, on placement at a small plant. We have a test rig built by a local panel shop last year, a pump and a small VFD. The E-stop is a red 22 mm pushbutton, flat, an 800FP I think, one NC block into a 440R safety relay. Press it, the relay drops out, the pump stops.

An auditor came through last week and flagged it as "not an emergency stop device". My supervisor says add a second NC block and it'll be fine.

I checked the button ten times with the relay, it drops every time, and looked up ISO 13850 on the college portal, where I only got the abstract.

It's NC, so if a wire breaks it fails safe. Photo of the button attached, but what's the difference between that and a "real" E-stop, or am I missing something obvious?

Conveyor restarts by itself when the guard door closes, no reset press, GuardLogix cell

twostroke — Sat, 19 Sep 2026 14:47:49 +0000

New cell from an integrator, commissioned last month. Conveyor inside a fenced cage, one guard door with a 440K tongue switch, safety on a Compact GuardLogix 5069-L306ERS2.

Open the door, conveyor stops, fine. Close the door and the conveyor starts running again on its own, no reset press, nothing. Our safety guy watched it happen and went pale. If you're inside the cage and someone shuts the door behind you, it runs.

I checked the door switch, actuator, tongue and mounting, all tight and clean, and it makes and breaks like it should. Production's suggestion is a horn that sounds before it restarts.

Our laptop guy is off this week, but I can get online with the spare if somebody tells me what to look at. Pretty sure it's not the switch, any pointers?

GuardLogix safety signature missing after a standard online edit, nobody touched safety

jcasey — Sat, 19 Sep 2026 14:43:33 +0000

Palletiser cell, 1756-L73S with the L7SP partner, Studio 5000 v33. Our monthly check compares the signature on the Safety tab against the one in the validation binder. This month there is no signature at all and Safety Status says the task has no lock on it. Last month it was locked, with a signature dated from commissioning.

Nobody has edited the safety task as far as I can find. The one online session in the last month was a contractor changing a standard rung for a reject pusher timer, and he says he never went near safety. I compared the safety routines against the archived ACD by eye and they look identical.

So where did the signature go, is it a firmware thing? Not sure if I can just generate a new one and lock it or if this needs to go further than me, could someone explain?

Two E-stops and one guard door, safety relay or Compact GuardLogix for a small cell

ollyb — Sat, 19 Sep 2026 14:43:27 +0000

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?

PNP prox on an ET 200SP F-DI safety input, short-circuit to P fault from the first scan

bram99 — Sat, 19 Sep 2026 14:37:53 +0000

Hi folks. Internship at a plant, TIA V17, CPU 1512SP F-1 PN with an ET 200SP F-DI 8x24VDC HF. My supervisor asked me to wire a proximity sensor on a sliding gate into a spare channel on the F-DI, so the safety program knows the gate is closed before the robot can move.

The sensor is a normal M18 inductive, PNP, three wires, black into DI3. From the first scan the channel is passivated, buffer says "Short-circuit to P, channel 3". The sensor LED works fine when I hold metal to it.

So I tried a second sensor out of the box, same fault, then moved it to DI5 and got the same again. My supervisor says turn the "sensor supply test" off for that channel and keep the sensor.

Sorry if this is basic, but are both of them broken, or am I missing something obvious?

ET 200SP F-DI 8x24VDC HF passivates a guard door switch with a discrepancy error

tomhw — Sat, 19 Sep 2026 14:37:52 +0000

TIA V17, CPU 1516F-3 PN/DP, ET 200SP with an F-DI 8x24VDC HF. Machine we shipped in spring, a rotary indexer with one guard door, mechanical interlock with two NC contacts on one actuator, into channels 0 and 4 as a 1oo2 pair, equivalent.

Customer rings, the door passivates a few times a shift. Their buffer says "Discrepancy error, channel 0" and then "Channel fault resolved" a couple of seconds later, always while the door is being closed, never when it's sitting shut.

So I went to site and put a new switch of the same type on, same fault by the afternoon. Checked the wiring at the BaseUnit and at the switch while I was in there, both channels tight.

Their electrician's pretty sure it's a bad batch. I'm not. What am I missing on the F-DI side?

SISTEMA gives PL c for a Cat 3 door interlock on an S7-1500F, needed PL d

ines31 — Sat, 19 Sep 2026 14:33:16 +0000

Commissioning a palletiser cell, the customer's risk assessment says PLr d on the guard door, and I built the SISTEMA file the way the drawings show: a Siemens 3SE5 mechanical interlock with two NC contacts, both channels into an ET 200SP F-DI with cross monitoring on, CPU 1512SP F-1 PN running the logic with blocks from the Siemens library, and two 3RT2 contactors in series switched from an F-DQ.

SISTEMA keeps coming back PL c. Category shows 3, MTTFd high, and it's still c.

I tried swapping the switch for one with better B10d numbers, still c. Thought about a second safety relay in front of the contactors, but that felt like guessing so I stopped.

Not sure if its the switch subsystem, or something in how I entered the F-CPU, or neither. Could someone explain what's holding it at c when the category comes out 3 and MTTFd is high?

PNOZ X3 safety relay drops out for a second every time the 30kW mixer drive starts

ramonv — Sat, 19 Sep 2026 14:33:15 +0000

Morning, mixer cell, powerflex 755 30kw on the main mixer motor. every time the mixer starts the safety relay drops for about a second, k1 k2 leds blink off, the whole cell stops and we walk over and reset. relay is a pilz pnoz x3, 24vdc version. started maybe two weeks ago, nobody changed anything they will admit to.

i metered 24.1VDC at a1 a2 sitting still and both e-stop channels at 24VDC, and went round all six e-stops with a screwdriver at 03:00 because the supervisor said loose wire. not loose.

the drive guy says the 755 throws emc noise on start and i should put ferrites on the e-stop wires. that doesnt sound right to me but im not sure why.

is this noise or is the relay on its way out, any suggestions?

GuardLogix safety signature, auditor wants it in the validation file, what is it actually

rookie_ray — Sat, 19 Sep 2026 14:22:47 +0000

Inherited plant, first year, nobody documented anything. We have a safety audit next month and one line on the auditor's list says "safety signature recorded in the validation file for each safety controller". Nobody here knows what that is.

Our line has a 1756-L72S with 1734 IB8S and OB8S modules. I went online with Studio 5000 v32 and found Controller Properties, Safety tab, and there's a long hex number with a date and time next to it, and a padlock icon.

I searched it and got a licensing page for something unrelated, and the maintenance manager reckons it's a password.

Is it a password, a licence, or something else, could someone explain, and what do I write down for the auditor, and who is supposed to sign it off?