Mesa 7i96 mixed voltage field input wiring

Hi,

A quick query, probably a silly question but wanted to get confirmation before continuing with this.

I have a situation where in need to mix both 5V and 24V voltage levels on the isolated inputs on the top section of the Mesa 7i96. I have proximity sensors at 24V and some other inputs from optical switches at 5V levels.

I could move the 5V stuff to general GPIO pins but I'd prefer to leave these as is if possible as it would require significant rewiring in my situation.

Am I okay to common connect the GND's from both the field 5V and 24V PSU's to the input common GND? (proximity switches are NPN so it will work from that perspective in my case).

Just to note that the main Mesa card is on a separate 5V supply from the field wiring noted above just to clarify (it has it's own 5V supply not used elsewhere) so it shouldn't compromise the isolation, so to speak. 

Thanks in advance, John

That should be fine

Great, thanks PCW.

I have just recently ordered a 7i96s and I'm trying to get my ducks somewhat lined up prior to its arrival. I am just wondering if the 7i96s would tolerate the same ie. commoned supplies like the 7i96.

Also, would it be OK to use a single 5V supply for both the Mesa supply and some external opto isolated field IO along with the 24V for the other field wiring?? Or is that just asking for trouble?

thanks in advance.





 

7i96 and 7i96S should be the same, the difference being the controler chip.
So any wiring should be the same.
Still, wait till PCW chimes in, he is the Mesa Master.

Yes, the 7I96/7I96S isolated input circuits are identical.

To use mixed I/O voltages you need sinking inputs
(7I96S isolated input common connected to
negative of field supplies and inputs connect to +
to activate)

The main disadvantage I see with using 5V field wiring
is an inadvertent short to say +24V...