short circuit monitoring on 24 dc DI modules

Has anybody used to for short circuit monitoring with 1756-IB16D,24vDC DIGITAL INPUTS(Diagnostic modules).Manufacacture talks about open circuit only.

You can do it with an analog card and a couple of resistors at the
feild device. You can detect on, off, open, or short.

What is the difference between a "short circuit" and an ordinary True condition on an Input module ?

Here, Here!!!

As far as I know, there is no 'Short Circuit Detection' (SCD) on the diagnostic input modules. There is however, 'Open Circuit Detection' (OCD).

Ken succinctly stated it above, that you really cannot determine a field-wiring short on an input module, but didn't get into the 'Open Circuit Detection'.

Basically, for the diagnostic input modules, OCD must be first enabled in the module, for a specific channel, and then, you put a loading resistor across the field device. Note, that the loading resistor may not be required if the field device is a solid state switch that has some leakage. The module will then be looking at all times for current flow... tiny current = device is open, large current = device is closed, no current = there is an open in the field wiring (or the leakage/loading current is insufficient).

Decent 'burglar alarm' type systems do indeed employ both OCD and SCD, but as stated above, it's a bit more complicated, and requires an input that can resolve 4 states.

I've always found a blown fuse as a pretty reliable indicator of a short-circuit; but that's just me.