Mesa 7i96 mixed voltage field input wiring

Assuming a 24V field voltage and conventional current flow for simplicity.

Sourcing inputs have the input common tied to +24V (so they "source" current)
They are activated by connection to ground (a sinking or NPN type sensor)

Sinking inputs have the input common tied to ground (negative of the 24V supply so they "sink current)
They are activated by connection to +24V (a sourcing or PNP type sensor)

A sinking sensor must be matched with a sourcing  input and vice-versa.

Maybe a diagram will help:


(Diagrams such as these could make a huge improvement to the Mesa manuals IMO.)

Edit: cuz PCW's 100% right. A brain fart had me spun around on sinking and sourcing.

I will say that the comment about the manual section is a bit misleading. The case of a PNP switch doesn't imply that switches have a common positive, just a "less positive" reference. not sure that saying a "negative reference" is correct to say.

The issue is that ground is common for sinking inputs but the + voltage is the reference
for sourcing inputs.

With sourcing inputs, when you have contacts or NPN sensors,
having a common say 24V reference is fine (since the inputs will
swing the full 24V) but they will not work with 5V outputs (say a MPG).
I guess you could use a 5V common but that is marginal with switches
and NPN sensors with indicators (which have a built in pullup to 24V)

With sinking inputs you have none of these issues with mixed voltages.

No, once you corrected me in typical PCW fashion I realized you were right on both accounts. Trying to fix my brain to say "sourcing" for positive is gonna be a challenge.....I've been saying it wrong for years lol.

But that's what I mean about the manual page, it pretty much says the same thing thing for NPN and PNP where it is correct for NPN but PNP the sensors just have to be more positive than the input common pin, not that they need to be connected as a common positive between each other.

A negative (ie -15v) input common would be a really tricky thing to explain when the positive input would be the 0v common of other things in the box.

PCW, how do you solved that inputs can source and sink (depends on one comm pin voltage/ground) and also can source/sink 5-36V range? I am definitely not master electronic engineer like you, but need to solve a simmilar issue. Some schematic?
Thank you.

Typically you can only use mixed voltages with sinking inputs (input common grounded)
In this case, any positive input voltage from +5V to +36V will be detected by the 7I96
isolated inputs.
 

I get the general principle of inputs in your MESA cards, I understood. You have made a very simple and easily understable manuals with you cards, btw.

But I am trying to solve simmilar inputs possibilities in one of my arduino wirings. I would like to have a little universal solution like you have on 7i96 cards, not just TTL as usual, but cant figure out what parts is best to use to achieve this.

Here is the 7I96/7I96S input circuit

Notes:

1. The quad optos are AC input type

2. The solid GND symbol is input common