Input types for A-B 1756-IB16 Input Module

Every now and then, you get asked a question that humbles you and makes you realize just how much more you've got to learn! I was just asked one of those questions... here it is?

"Does the attached Digital Output module supply the output you are expecting on your Input module?"

This is a contractor asking me if a new module they will be supplying in their new system will work with my 1756-IB16 modules to provide some DI's for us.

The "attached" as he calls it is attached. The .pdf doc refers to several different output types starting with CURRENT SINKING and so on...


My answer is ... only way I've ever wired these modules is dry contacts where it's looking at its own DC coming back. Please pass down any wisdom you may have.

I would always advise on putting interposing relays between any two hardwired systems. Also you easily avoid any issues with Voltages, meaning two different systems normally have different power supplies and you cant just mix and match.

It makes life easier for testing and is good practice in my opinion.

Rheinhardt

Since the 1769-IB16 expects a sourcing signal and the supplied module is a sinking type you need to calculate if the pull-up resistor pack can supply enough current to activate the IB16 inputs. Even then you would have to reverse the logic since a logical ON from this module would be a logical zero to the input. If not you may have to provide isolation relays.

you'll probably find the 1756-IB16I easier to work with ... the "I" on the end tells you it's an "isolated" module - so you can use sinking or sourcing - and as long as safety isn't an issue, the isolated will be easier to interface with other systems ...

http://literature.rockwellautomation.com/idc/groups/literature/documents/td/1756-td002_-en-e.pdf

see page 21 for the wiring - and page 22 for the specs ...

pay careful attention to the specs for "On State" and "Off State" conditions - particularly with respect to how much voltage - and how much current - will reliably be registered as either On or Off ...

Thank all you gentlemen for your wisdom. I got a little bit out of each of your posts which is enough for me to do some checks and come up with some kind of answer for this fellow. I love this fourm. :site:

Thanks again.