Acromag manufactures 4-20mA Signal Isolators. There are several different types to choose from:
2 Wire Loop Powered Isolators
|3 Wire DC Powered Isolators|
4 Wire AC / DC Powered Isolators
4-20mA Loop-Powered Isolators, 2-Wire Models get power from the 4-20mA output or input loop (sinks or sources current). Typical uses are as a current repeater or to drive resistive loads.
DC-Powered Isolators – These models are used to drive resistive loads (sources current). The 4-20mA output signal and DC power share a common lead which is wired directly to the PLC/DCS’s internal ground.
4-Wire AC/DC-Powered 4-20mA Isolators – These isolators provide 3-way isolation to separate input, output, and power circuits. They are safest for retrofitting or expanding systems where instrument isolation or the grounding schemes are unknown.
For more information on the different signal isolators 4-20mA ; please see below or contact us.
Or to learn how to choose the right isolator for your application – check out this blog titled “Selecting the right signal isolator”
4-20mA Loop Powered Isolators, 2 Wire
Models get power from the 4-20mA output or input loop (sinks or sources current). Typical uses are as a current repeater or to drive resistive loads
651T and 250T models are ideal for applications that require an isolator with a power supply in series with the output signal. Power is obtained from the output loop. The isolator must control current draw from the power supply in the output loop which is the 4-20mA signal. Since output and power share the same two wires, this type of isolator can be placed anywhere between the field sensing device and the PLC/DCS or monitoring device. Usually, the isolator is located close to the field device. Since both the input and output signal are 4-20mA, location of the device is not critical.
670T and 270i models are useful when adding and isolating a monitoring instrument to an existing current loop. When adding a field device such as a recorder or display, no additional power source is required for the added loop or for the isolator. The isolator’s output is powered by the input loop power and drives passive loads only.
These models are used to drive resistive loads (sources current). The 4-20mA output signal and DC power share a common lead which is wired directly to the PLC/DCS’s internal ground.
3 Wire DC Powered Signal Isolators
Acromag’s 340i model is ideal for applications requiring multiple isolators at a single location where all isolators share the same power supply. PLCs and DCSs usually have 24V DC power available at their input terminals.
4 Wire AC / DC Powered Signal Isolators
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 signal isolators source current out and do not use a separate output power supply. The outputs are designed to drive purely resistive loads.
The isolator can be located several or hundreds of metres 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 analogue outputs, the PLC/DCS output is wired to the isolator input and the isolator output is wired to the field device/actuator.