[foxboro] IOBAD
- From: "Lowell, Tim:" <Tim.C.Lowell@xxxxxxxxxxxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Tue, 7 Oct 2003 14:51:19 -0500
List,
We are going through an alarm rationalization process using the EEMUA =
standards, and the one aspect of the Foxboro DCS alarm system that we =
are having the most trouble dealing with is IOBAD for AIN blocks. =20
We get a lot of nuisance IOBAD alarms during upsets that are not really =
indicative of hardware failures. They are really Out of Range =
conditions. The transmitter and FBM are working fine, but the signal is =
either below or above the configured range. We have BADOPT set to 3, =
the default, which means Out of Range High or Low or Bad FBM =3D BAD. =
What we need is to be able to differentiate from an Out of Range =
condition and an actual transmitter failure, meaning the wire is cut or =
the transmitter loses power, i.e. no signal. When we get an Out of =
Range condition, we want to get only an Out of-Range Alarm, set the BAD =
bit which in turn puts any connected PIDA in HOLD or Manual, and not get =
an IOBAD alarm. When the transmitter actually fails, we want the BAD =
bit to be set which puts any connected PIDA in HOLD or Manual and to get =
only an IOBAD alarm. Unfortunately, BAD and Out Of Range seem to be =
inextricably linked in the I/A. Using the BADOPT parameter, it doesn't =
look like you can configure the system to set the BAD bit during an Out =
Of Range condition without also triggering an IOBAD alarm. Am I =
interpreting this correctly or am I missing something?
Has anybody else on the list gone through the EEMUA alarm =
rationalization process? What do you do with IOBAD alarms?
Tim Lowell
Control Systems Engineer
ConocoPhillips, Trainer Refinery
Phone: 610-364-8362
Fax: 610-364-8211
Tim.C.Lowell@xxxxxxxxxxxxxxxxxx
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