6246189 - 

RS-232 Current Loop Converter
The Patton Model 2018 is an optically isolated, multi-function RS-232 to 20mA current loop converter: Hook it up to an active 20mA current loop circuit and it's a passive converter. Hook it up to a passive 20mA current loop circuit, add DC power to one of several DB-25 interface pins, and it's an active converter. Connect two units together, supply DC power to one interface, and it's an optically isolated RS-232 distance extender.
Operates Actively or Passively
Data Rates from 50 bps to 19.2 kbps
Range to 4 Miles (6.4Km) over Two 24 AWG (.5mm) Twisted Pair
No AC Power Required; Draws Necessary Power for (Passive) Operation from RS-232 Interface
External DCE/DTE Switch
Optically Isolated on Line Side
Two Units Work Together as Optically Isolated RS-232 Distance Extenders
Asynchronous communication