Answer / carl_ellis

Failure to connect with HART can be a laundry list of
issues, the most common of which is the

lack of minimum 230 ohm resistance in the loop.
Other reasons can be
- HART probes connected across the DC power supply, not in
the loop
- failed DC power supply
- electrically noisy DC power supply
- HART modem lacks installed PC driver or internal setup
(serial modems were touchy)
- HART device not at expected HART address (address zero for
point-to-point comm)
- device does not have HART option or HART option has been
disabled.
- HART option replaced by different fieldbus comm card (it's
happened! !)
- Connecting across the test terminals on a pressure
transmitter where there's no HART signal
- HART communicator is dysfunctional or its batteries are
discharged
- lack of DD in communicator/program limits access to the
common commands

Carl Ellis
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