This signal conditioner provides the galvanic isolation between field circuits and control circuits. The device repeats the input signal from a control system to drive SMART I/P converters, electrical valves, and positioners located on the field side. Digital signals are superimposed on the analog values at the field side or control side and are transferred bi-directionally. The current is transferred via a DC/DC converter and repeated at the output terminals. An open field circuit presents a high impedance to the control side to allow alarm conditions to be monitored by the control system. Test sockets for the connection of HART communicators are integrated into the terminals of the device.