OK, here is another option, given that I have not seen any mention of transmission latency. Rather than convert a binary word into an analog voltage, why not have each input that is active set a specific voltage in one volt increments, so that outputs will be identified by a specific voltage from one to nine volts, and then an analog scanner sequentially selecting each point in sequence. Then on the receiving end each specific voltage reading can set a bit indicating which contacts are active. That scheme can simply be multiplexed by an analog data acquisition scanner, and on the receiving end be recorded as set bits entirely in software. And the whole system will not need to be synchronized.

 

Well, this would be indeed a good design, but again, the only solution I have is a 4-20mA level. I don't have any control on the Monitoring system.

From my initial question, I guess I am going to use an arduino even if I would have preferred an industrial design.

Thanks for the inputs

I don't understand why are you stuck with the 4-20mA loop. You will need to design both the encoder and decoder so would it not be simpler, more reliable and less expensive to use a digital bus, especially in the quantities you have mentioned.

 

Exactly the same scheme that I described could be set up to provide eight different current values, based on eight resistors. it would exhibit only a small amount of delay and it could be very stable.