I'm a PC software guy, a newbie to electronics. Recently, I've got a project in which I need to source for a DAQ that can provide dry contact inputs to an interfacing digital output controller. The controller generates alarm signals. I've uploaded the system diagram here -
Link to larger image: http://i.stack.imgur.com/KL88h.png
As shown in the diagram, the digital outputs are Form A relays that "are closing contacts with one common terminal (C) and one normally open terminal (NO). The terminals are isolated from signal ground.". So the digital outputs are normally open and I suppose will close only when there's an alarm. It is not indicated in the data sheet whether the digital outputs are wet or dry.
Here's how I figure it will work:
If the digital output relays are open, my dry contacts will not form a circuit. If the digital output relays are close, my dry contacts will become a closed circuit and current will flow because the digital outputs are rated 250VAC/30 VDC, 2A??
But dry contacts are not suppose to have voltage or current? I can't figure how this part works out and will appreciate any pointers. Thank you.