Machine Integration

Im attempting to integrate a machine into a production line. The master machine has a terminal box with 1734 point i/o all pnp inputs 1734-IB8. The slave machine has its own controls and power supply that are npn style outputs. What would be the best option to get npn outputs from the slave machine to the master. I have seen the input card option 1734-IV8. Not sure if this will cause issues with two different power supplies feeding each machine. Would the common side of each power supplied have to be linked together for a common refferance signal?
I would appreciate an suggestions.

Thank you

If both power supplies are grounded I guess ut works but I wouldn't do it. Do you have to exchange many signals? My suggestion would be using interface relays.

I believe eight inputs and eight outputs would do the trick. If I installed a 1734-AENT in the slave machine and used its own power supply would the ethernet communication be okay?
It would be an expensive alternative but I'm really trying to minimize dry contact isolation methods.

thanks for the feedback.

For your consideration:

http://http://www.dot-as.dk/files/npn-pnp_new.pdf

Are both machines capable of ethernet comms? Can you use Messaging, Produced/Consumed tags, or do you need hardwired signals? For hardwired, I tend to use the slimline AB or Phoenix solid state relays.