How to detect faulted or broken wires for PLC inputs
How to detect faulted or broken wires for PLC inputs
(OP)
I have a PLC with several inputs to various field devices with open/closed contacts such as limit switches and proximity switches. For some time now, I've been trying to figure out a way to detect a faulted or broken control wire to one of these devices. To me, the PLC would see would see faulted control wiring as a closed contact and a broken wire as an open contact. This could be bad for my system and I'm looking for ways to protect against it. Any ideas?





RE: How to detect faulted or broken wires for PLC inputs
TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering
www.bluetechnik.com
RE: How to detect faulted or broken wires for PLC inputs
If your prox was the forward position prox, then make logic when the prox is made with the cylinder in the forward positon.
xio prox xic ForwCylinderSolv timer on delay 2sec = latch fault
In the above logic when the cylinder is in the forward position the prox is not made in 2 secs then latch fault the machine.
Create same logic for the retracted position of the cylinder
I have been to so many places that do not do this makes me ashamed to be a controls engineer.
RE: How to detect faulted or broken wires for PLC inputs
RE: How to detect faulted or broken wires for PLC inputs
Thus, a circuit that sources a current into the switch contact can produce, say 5V for a complete open, 2.5V for a normal open, and 0V for a normal close.
TTFN
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RE: How to detect faulted or broken wires for PLC inputs
RE: How to detect faulted or broken wires for PLC inputs
You will need an AI instead of a DI for each circuit which might get expensive depending on numbers and/or PLC used
RE: How to detect faulted or broken wires for PLC inputs
Controlsdude, I am looking around for modules that have this built in feature and think I have a couple of options.
Before I posted this topic, I came across a company that sells separate modules specifically to detect these conditions. They work with the PLC I/O rather than replace it so, its a lot of added hardware. They use zener diodes rather than resistors but function off of the same idea, I think.
RE: How to detect faulted or broken wires for PLC inputs
It's good practice to always make sure a switch fails to the safer state. More often than not a switch will fail to the open not closed.