IO Module Selection

Hey all,

I've done mostly PLC programming work and not much design. I have a question about IO module selection. I know there are different types of modules like
24VDC digital input, 24VDC digital output, 120VAC digital input, 120VAC output...sinking/sourcing I/O, isolated I/O, relay outputs cards....etc. etc. etc.

My question is how do I know which one of these to select for a particular piece of equipment? I understand stuff like analog inputs and outputs cards since there's not too much selection for that. But i'm a little confused when it comes to selecting whether a digital I/O should be 24VDC or 120VDC, sinking, sourcing etc.

I'm trying to get IO to a watermain Gate valve that has an actuator. The I/O I need are:
Valve Command to Open
Valve Command to Close
Valve Opened
Valve Closed
Valve Fault

For UPS
UPS Fault

How do you find out which I/O cards these should use? Does anyone know of a guide that is out there?

Thanks!

The electrical needs and capabilities of the external equipment determines what you need in I/O. Get ALL the information for these pieces of equipment.

If they have links on the web provide them to us so that we may help. The Sinking/Sourcing can be troublesome if specifics of the equipment is not supplied as different vendors use these terms differently.