The stacker's guard door switch went bad last month, so I replaced it with the same part number, two channel mechanical. Wired it back the way the old one was, through the little junction box on the door frame and into a 1734-IB8S, channels 0 and 1. GuardLogix is a 1769 L30ERMS.
Now every time the door closes the module faults that input. Studio 5000 shows a short to test output fault on channel 0 and the point status LED goes red. Open the door and it clears after a reset.
I tried a second new switch from stock, exact same thing, and checked the wires are tight at the module. The stacker's down until this is sorted.
Is the 1734-IB8S dying on those points? Two new switches did exactly the same thing though, so I'm not sure it's the module at all, is it something in that junction box on the door frame?
Before anyone starts looking at the test pulse settings, leave them alone. That fault is the module telling you something real. Which test outputs are channel 0 and channel 1 sourced from in Module Properties, T0 and T1? And in the junction box on the door, how many terminals do the two channels go through, four or two?
T0 for channel 0 and T1 for channel 1, that part I did not touch. In the JB it is a little strip with three terminals. Two channel wires come in from the switch on one side, and I put the two panel wires on the other side. I think the old switch was on the same strip.
Three terminals for four wires. Which two share?
Take the switch off the strip and put your meter across the two panel wires at the JB, ohms. If you see near zero, your channels are tied together before they ever get to the module.
Meter across the two panel wires with the switch disconnected reads 0.3 ohms so they are connected somewhere, but the old switch worked for years on this same box.
They were probably not tied together before. Doesn't matter now.
Both channels on one terminal or one crimp lug means T0 and T1 pulses see each other. The module pulses T0 low for a moment, expects only channel 0 to drop, and channel 1 drops with it. That is the short to test output fault, and it is exactly what the IB8S is there to catch. A door switch with the channels bridged is a single channel switch pretending to be two.
Separate them. Two terminals per channel in that box, nothing shared. Then reset. Someone did a decent article on wiring these up here: https://plctr.com/implementing-plc-safety-interlock-systems-in-industrial-environments/
Opened the JB properly this time. The two wires from the panel were in one crimp lug together, someone had ferruled them as a pair, and that pair sat on terminal 2 with one switch wire. Put in a four terminal strip, one channel each side, reset, door closes clean. Ran all shift.
Never the 1734-IB8S, and never the switch. Both channels were bridged in that box, which put the T0 and T1 pulses on the same wire, and giving each channel its own terminal sorted it.
What I still don't get is how it ever worked with the old switch. Maybe the old switch had something different inside, I chucked it so I can't check now. Thanks edj and garyb.
Marking solved. Module did its job.
plctr.com team