Re: [foxboro] Hart FBM's
- From: sssmith1@xxxxxxx
- To: foxboro@xxxxxxxxxxxxx
- Date: Tue, 24 Aug 2010 11:41:00 -0500
Corry,
We have experience similar "infant mortality" problems with FBM214 TA's
during recent commissioning. I believe we had 2 such failures. None
since.
Technician wrote up the below technote capture for future diagnostics of
similar occurrences in house.
During Foxboro Controls installation and testing, we experienced loss of
control on a piece of equipment utilizing 4-20ma current loop of an
FBM214. Hart communication in this instance is only utilized for a
feedback indication. Upon discovery of this malfunction, we replaced the
suspected FBM module with a new one with no change of symptoms noted.
Further investigation led us to suspect that the problem was in the FBM214
Termination Assembly. Utilizing a digital ohmmeter, we checked the
resistance readings across terminals ?A? and ?C? of each input. It was
discovered that the input in question read approximately 80K-120K Ohms, as
compared to a normal reading of 8+Megohms on known good inputs. Readings
were taken with the module deenergized and field wiring lifted. We then
replaced the TA, and the problem was solved.
We have experience other HART FBM issues as well.
Most recently, last week we encountered issue where ALL CURRENT values
from a FBM 214 ( EEPROM version 2.40D ) experienced an abrupt gain across
all channels of approximately 20-30 percent.
Foxboro TAC told us that this was a known issue ( No technical advisory
bulletin ever issued??????)
A EEPROM new EEPROM update was released on Friday last week (QF1013828)
that is supposed to partially address the issue. They still don't know,
and I don't believe have been able to replicate the problem in house, but
this has occurred at 4 customer sites. This could have been a very
catastrophic event, but fortunately, our IO and logic was partitioned and
segmented in such a way that disaster was averted.
We exclusively use CURRENT from the HART channels for control. Do not
poll HART signals. for RIN's. We do use RIN HART PV signals against our
215 hart AO's for deviation alarm purposes though.
During the HART AI gain event, the HART PV signal was unaffected, as
confirmed at the transmitter, via 375 hand held, and by PACWare
interrogation.
Scary to say the least.
I would be interested to lean who the other customers were that
experienced this A/D Gain, and how their systems were affected. And why
an advisory bulletin was never issued.
Foxboro??
Sheldon Smith
Office:972-884-2843
Cell: 214-460-4073
EFax: 866-734-2905
Conf: 877-253-4307 #7082843
Mailto: sssmith1@xxxxxxx
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