4-20mA Signal Isolators – 4 Wire AC DC Powered Isolators

Acromag 4 wire AC/DC powered isolators provide reliable electrical isolation between field instruments and industrial control systems. They accept a standard 4–20 mA process signal and deliver a corresponding isolated output to a PLC, DCS, data acquisition system, indicator or controller.

Unlike loop-powered models, these isolators use a separate power connection. As a result, the power circuit operates independently from the input and output signal circuits. This arrangement supports three-way isolation and helps protect sensitive equipment from ground loops, electrical noise and transient signals.

How Do 4 Wire Signal Isolators Work?

A 4 wire signal isolator receives a 4–20 mA input from a field device or process transmitter. It then reproduces the measurement as an isolated 4–20 mA output for the receiving control system.

Meanwhile, a separate AC or DC source powers the isolator. The required supply depends on the selected model. Therefore, engineers should confirm the available control-panel power before choosing an isolator.

By separating the input, output and power circuits, the isolator breaks unwanted electrical paths. Consequently, differences in ground potential cannot circulate current through the measurement loop and distort the signal.

Benefits of AC/DC Powered Isolators

External power gives 4 wire isolators greater flexibility for demanding signal-conditioning applications. For example, selected models can provide excitation power for a two-wire field transmitter or support multiple isolated channels within one unit.

Additional benefits include:

• Three-way isolation between input, output and power
• Reduced ground-loop measurement errors
• Improved protection against electrical noise and transients
• Reliable 4–20 mA signal transmission
• AC or DC power options across the product range
• Single and dual-channel configurations
• Compatibility with PLC, DCS and DAQ inputs
• Stable operation when output loads change
• Compact installation within control cabinets

Furthermore, many Acromag models include factory calibration and zero or span adjustment. Therefore, technicians can complete installation and future maintenance more efficiently.

Applications for 4 Wire AC/DC Powered Isolators

Engineers use externally powered signal isolators across manufacturing, energy, water, transportation and industrial automation systems. Typical applications include:

• Process control and instrumentation
• PLC and DCS signal interfacing
• Water and wastewater monitoring
• Pump and motor control
• Tank-level measurement
• Pressure, flow and temperature monitoring
• Power and utility systems
• Manufacturing equipment
• Remote field instrumentation
• Control-panel upgrades and retrofits

In addition, multi-channel isolators can save panel space where several process signals require independent isolation.

Choosing the Correct Powered Isolator

First, confirm whether the installation provides AC or DC power. Next, check the required input and output ranges, number of channels, isolation rating, accuracy, response time and operating temperature.

Also consider whether the field transmitter requires excitation power. Some externally powered isolators can energise a two-wire transmitter while retransmitting its 4–20 mA signal. However, model capabilities vary, so check the complete loop requirements before selection.

The Acromag range includes DC-powered, AC-powered and selectable AC/DC-powered configurations. Metromatics can help you compare models such as the 330i, 430i and 631T/632T series according to your signal, power and installation requirements.

Metromatics supplies and supports Acromag signal-conditioning products throughout Australia and New Zealand. Contact our team, to identify a suitable 4 wire AC/DC powered isolator for your application.