Answer / carl_ellis

1) How do you know that the device talks HART? Many field transmitters talk Brain, Honeywell DE, Foundation Fieldbus, Profibus or 4-20mA only.

Have you confirmed the HART functionality on that device?

2) Point-to-point (communicator-to-transmitter) is usually done with the device at address 0 and with the communicator polling address 0.
Is the communicator polling address 0?
Is the device at address 0?

3) On many transmitters, HART can be disabled. Is HART enabled on this transmitter?

4) The transmitter has to be powered, initialized and in its operating mode in order to communicate via HART. Sometimes transmitters are not powered, but when connecting from the a marshalling panel, it is obvious, because the transmitter is remote location. Is the transmitter powered and operating?

5) Are connections across the dropping resistor or across the transmitter's (+) or (-) terminals? Connecting across a pressure transmitter's 'test' terminals will not work properly for HART communication.

6) A loop isolator module that is not specifically designed for HART will strip off the HART signal, but pass the 4-20mA current signal. If a loop isolator is installed in the loop, is it designed for HART operation.

7) If the power supply ripple and noise exceeds the HART specification, the power supply noise will interfere with HART or prevent communication entirely.

8) The 475 can have 3 terminals at the top where the banana plug field cable plugs in. 2 terminals are for HART, 2 terminals are for Foundation Fieldbus (FF). If the cable is plugged into the 2 terminals for FF, HART communications will be blocked by not having a cable in the correct port.

Carl Ellis
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