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?
Nothing is broken. Part number of the sensor, the full one? And where does the brown wire go, the panel 24V bus or the VS sensor supply terminal for that channel on the F-DI? List the three wires exactly.
3RG4012 something, I'll check tomorrow, a Siemens M18 PNP NO. Brown: panel 24V bus, the one the standard modules use. Blue: 0V bus. Black: DI3. I didn't use the VS terminals, I didn't know what they were for.
Put a meter on the black wire with metal in front of the sensor. Solid 24VDC, out of the sensor's own supply. The F-DI pulls its sensor supply low for a moment and expects the input to go low with it. Yours can't, the sensor holds 24V from the panel bus. The module reads that as a wire shorted to 24V. Correct answer, not a fault.
Turning the test off leaves a channel that can't tell a shorted cable from a closed gate. A standard prox isn't a safety device whichever module you plug it into.
Two proper answers: a mechanical positive opening switch, two channels, test pulses on. Or a safety sensor with OSSD outputs, test off for that channel because the sensor does its own. Through a relay is no.
What does OSSD mean? And my supervisor still wants to keep the prox because it's "more reliable than a switch with moving parts".
Output Signal Switching Device, the pair of self testing outputs on a safety sensor or curtain. Reliable is not the question. The prox has no way to fail safe and no way to be tested. Wiring list for a proper one: two channels to two F-DI inputs, each on its own VS supply, test pulses on. Then someone has to do the risk assessment for that gate, before the robot part, not after.
Supervisor ordered a magnetic safety switch with two channels, a 3SE6 I think. I wired it as petra66 listed, each channel on its own VS terminal, test pulses on. No fault, channels follow the gate, safety program sees it. The prox is back in the box.
Neither sensor was broken and the module was never wrong. A standard PNP holds the input at 24V from its own supply, the test pulse never sees the input follow, and the module calls that a short to 24V. A real safety switch on a test pulsed pair and there's no fault at all.
The risk assessment for that gate is still "somewhere", I asked twice. Thanks marekw and petra66.
A prox tells you where the gate is. It doesn't promise.