Black Box CL1090A-F converters can be configured for active or passive Current Loop. In active mode, an async RS-232 device can communicate with a passive 20-mA Current Loop device. In passive mode, an async RS-232 device can communicate with an active 20-mA Current Loop device.
These compact solutions are configured as RS-232 (DCE), but they can be modified for DTE use with an asynchronous modem eliminator (ME212).
Each converter has a Transmit (T+ and T-) and a Receive (R+ and R-) loop. Optical isolators in both the transmit and receive loops keep out electrical interference and eliminate ground loops.