Micro820 on the bench here, the 2080 LC20 20QWB. The old NPN prox on my little conveyor died and I bought a PNP one out of the catalog because that's what was in stock. Brown to +24VDC, blue to 0V, black to input 0.
Input never comes on. The rung is just XIC _IO_EM_DI_00 OTE _IO_EM_DO_00 and the output never fires. So I tried a second PNP sensor, same nothing, then put a meter on the black wire and got 0V with nothing in front of it and 24VDC with metal there. The sensor is doing its job.
Is the sensor just wrong for this input, or am I missing something obvious about which way the current is meant to run?
You proved the sensor with the meter, so leave it alone. What's the common terminal for that input group wired to, +24VDC or 0V? That decides everything here.
The COM terminal for inputs 0 to 3 is on +24V. That's how it came from the guy I bought it off, not sure it was ever deliberate.
COM on +24 is the whole thing. That makes it a sourcing input, not a sinking one, different animal. With COM at +24 the module pushes current out of the input terminal, through the sensor, to 0V. That's what an NPN sensor wants, it sinks. Your PNP is trying to push 24V into a terminal that's already sitting at 24V. Nothing flows, no input.
On ours the input commons are a terminal you can move, check yours. Put that group's COM on 0V, now the module sinks and the PNP sensor sources into it. Or buy an NPN sensor and change nothing. Photo of our terminal block attached.
The sinking and sourcing bit with a drawing is here: https://plctr.com/understanding-the-basics-of-input-output-modules-in-automation/
Moved that COM to 0V and input 0 comes on with metal in front of it. But now inputs 1 to 3 with the old NPN sensors on them do nothing at all, no luck there. I think I've just moved the problem along one.
Correct, they share the common. One sensor type per group.
Put the PNP sensor on input 4 in the second group and took that group's COM to 0V. First group's COM back to +24V for the three NPN ones. Everything reads now.
I had it backwards from the start. A PNP sensor into a group that's wired to source means both ends are pushing and nothing moves, so the PNP gets its own group and the three NPN ones keep theirs.
Still don't know what the status bit next to the input in the tag monitor is telling me, but it's on. Thanks mike, marek.
Sink or source means you pick. Per group. Good call on the NPN ones.