These isolators provide 3-way isolation to separate input, output, and power circuits. They are the safest choice when retrofitting or expanding systems where instrument isolation or the grounding schemes are unknown. These 3-way isolators source current out and do not utilize a separate output power supply. The outputs are designed to drive purely resistive loads. The isolator can be located several or hundreds of feet away from the PLC/DCS and obtain power from an external AC or DC source. This source may have a different ground potential than the PLC/DCS or field device. In this case, the power ground must be isolated from both the input and output. Across long distances, the ground potential at a sensor is likely different from the power source and PLC/DCS. Consequently, input to output isolation is also necessary. Additionally, these units can isolate 4-20mA control outputs from the PLC/DCS to field actuators. In the case of analog outputs, the PLC/DCS output is wired to the isolator input and the isolator output is wired to the field device/actuator.