Rosemount 3300 Transmitter/MTL7206/HART Tri-Loop Converter


Thread Starter

Danny Mc Ginty

Field Transmitter is a Rosemount 3300 measuring level and oil/water interface. sending a 4-20mA to our Honeywell 3000 DCS. We are using a (Rosemount) HART Tri-Loop to convert the digital signal to a second 4-20mA. The use of the (recommended) MTL 7206 seems to 'block' the digital signal. The circuit is I.S. Tried MTL 728/707 but, still had problems. Any suggestions???


Danny McGinty

For anybody interested, the problem was that the zener diode type barrier (0 Volt reference) was messing up the digital HART comms signal, going to the Tri-Loop. We installed an MTL 5042 (galvanically isolated) repeater power supply and it solved the problem.

Jonas Berge - F

I think it is important to add that the difference is probably not (zener) "barrier" vs. "isolated" (barrier). The difference is that a particular model has been designed for HART communication. That is, the barrier/isolator must have circuitry inside to carry the HART signal through. Not all barriers/isolators do this. If you are using HART, you should look for this regardless of the supplier.

This applies to any HART master device sitting on the safe side communicating with the hazardous side, including our (SMAR) HCC301 HART-to-current converter and HPC401 communicator.

To learn more about HART in hazardous areas take a look at the yellow book "Fieldbuses for Process Control: Engineering, Operation, and Maintenance" buy online: