Dears,

We plan to install a coriolis flow meter at our plant, which will be powered by a separate 24VDC power supply. The readings will be transmitted to the controller through Exi birrier MTL 4544A.
Can you tell me if it is possible to use the 4544B barrier instead of the 4544A?

 

You want to install a Coriolis flowmeter, which evidently has an Intrinsically safe 4-20 mA output signal.
Now, with a few exceptions, Coriolis flowmeters are 4 wire field devices, because their oscillating tubes requiere more energy than what a usual intrinsically safe transmitter power supply kind of barrier can deliver. 4 wire devices use 2 wires for power and 2 wires for the 4-20 mA output signal. The thing is that 4 wire Coriolis flowmeters feature an active current source powered by a built-in galvanically isolated barrier inside the device's housing. Therefore, you require a passive input barrier to receive the active 4-20 mA. That is, the IS barrier employed must work in sink mode.

MTL's 4544A is barrier is a current repeater, i.e. its 2 inputs work in sink mode and match the active or source mode of the Flowmeter's output.
MTL's 4544B is barrier is a transmitter power supply for either 2 or 3 wires transmitters. It works as current source, or in other words, is an active output.

Conclusion: unless the Coriolis flowmeter is a loop powered device, and the majority of them are not, you cannot use a transmitter power supply with active outputs because it would mean to connect two power supplies together.
You must use a current repeater with a passive input which acts as a current sink.

You cannot use a 4544B barrier for this application, you must use a 4544A barrier.
The corresponding datasheets are attached.

Mirko Torrez Contreras
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