I think most here would want to know your data rate (i.e. how many
bits of resolution are you reading with, and how often?)  Sounds a LONG
way for RS-485, perhaps current loop (Ick, I know <G>) if slow enough
baud rate here?  Also using a "Leased Line" modem pair would perhaps
work, if you can find good modems for the job (ZyXEL's did it for me,
once.)  What's cheapest, would take more data for an optimized answer
here.

  Mark

Pedro Drummond wrote:
>
> Hi, folks.
>
> What is the best way to keep track of a 0-24V instrument from a distance of
> 2 miles (approx. 3 km) ? I have wires from point to point, already. Well, I
> have a PLC at the monitoring station, but I guess I can't help but add some
> treatment to the signal at the source and then send it digitally. What is
> the max. distance for a RS-485 interface ? Am I forgetting something ?
>
> Best wishes,
>
> Pedro.