Was hoping to get some insight into diagnosis and troubleshooting of a signal error I am seeing. I have a (calibrated) Rosemount 1151 wired to an AI 4-20mA HART CHARM.
With the instrument at 4.0mA output, I am seeing a 0.5% (4.08mA) at the AI. With the instrument at 20mA, I see 102.2% (20.35mA) at the AI in DeltaV.
This behavior has been duplicated by removing the instrument from the loop, and sourcing 4/20 from TREX.
Here is a screenshot of the CHARM in Diagnostics with the Instrument at 4.0 mA:
Greetings Friends -
So for the long awaited update - After a week of "burn-in", I was able to get help checking this loop again.
The first step was to interpose a calibrated Fluke meter in the loop. This was done at the CHARM. The previous error was present UNTIL the loop was opened, and the Fluke was interposed.
As soon as the Fluke was interposed, the error disappeared and we verified - Transmitter sourcing 4.01mA, Fluke seeing 4.01mA, and we see 0.08% at the Charm (4.01mA).
Testing the span, transmitter at 20mA, the CHARM sees 99.99% (20.0 mA)
We literally have no problem, no error at 4 or 20mA now.
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Here is a trend of the PV with the error disappearing after the first loop break.
No idea what was reset by opening and closing the loop, but we now have the expected and desired loop behavior.
In reply to SimHogan:
Andre Dicaire
In reply to Andre Dicaire:
Hello Andre On the first step we did not isolate the field wire, as we were trying to verify the observed error. We were intending to isolate the field wire as a second step, and swap CHARM was the third step. We interposed the Fluke into the field wire loop at the CHARM, and at that moment, we ceased to see the signal error. We then removed the Fluke, and the correct signal was still observed. Since the error disappeared in step one, it left me with nothing to prove/disprove by isolating the field wire. Since we had a spare CHARM on hand, we swapped the CHARM and continued to observe the same, correct signal. I cannot explain the phenomenon. Possibly opening the loop to insert the Fluke caused something with the transmitter to reset? Since opening and closing the loop is essentially a transmitter reboot... Maybe there is a sheild/grounding/connection issue that resolved when we disconnected/reconnected?