1. Why HART isolator barriers?

The loop condition may not always be predictable at the beginning of your application. There are instances when input cards are in an active state and others when they are passive. You can potentially connect a transmitter to a line power supply with four wires, which typically has active outputs, or to a two-wire passive power supply.


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2. What happens when we power a loop with 2 different power supplies?

When two devices, such as a 4-wire HART transmitter and a DCS, attempt to supply power to the same loop, it leads to a malfunctioning loop. This is the point at which we begin employing a HART isolator barrier.

3. Using a HART isolator barrier with Rheonics devices.

Rheonics SME has self-powered 4-20mA analog outputs. This means that any connection to a controller device must be considered as a 4-wire transmitter. A 4-wire transmitter consists of two power wires and two signal wires. The two power wires supply the power to the transmitter, while the two signal wires transmit the signal back to the controller device. 

Figure 1. Wiring diagram with HART isolator barrier.

4. Recommended barriers

4.1. RN42 (Endress + Hausser)

The active barrier serves the purpose of transmitting and providing galvanic isolation for 0/4 to 20 mA/HART signals. This device features an input with both active and passive current capabilities, allowing direct connection of 2- or 4-wire transmitters. You can choose to operate the device's output in an active or passive mode. The resulting current signal can then be accessed at plug-in screw terminals or optional push-in terminals, making it available to the PLC/controller or other instrumentation.


Figure 2. RN42 HART isolator barrier.

4.2. HIT/HIX (Moore Industries)

These isolators available in a 2-wire, loop-powered version(HIX), and a 4-wire, mains-powered configuration(HIT), serve the purpose of interrupting the shared electrical (galvanic) connection between a HART transmitter and one or more receiving devices within a process instrumentation loop.

Figure 3. HIX isolator barrier.

4.3. LB4002A2 and FB4302B2 (Pepper+Fuchs)

The LB4002A2 HART isolator barrier is specially prepared to be used in Intrinsically safe applications where it is required to be installed in Zone 2 or safe zone.

Figure 4. LB4002A2 Isolator barrier.

The FB4302B2 HART isolator barrier is specially prepared to be used in Intrinsically safe applications, it can be used in installations suitable for enclosures in Zone 1.


Figure 5. FB4302B2 Isolator barrier.

5. References