That sounds like a pretty reasonable request to me Jimmy. Holding an analog
output in last value with no way to override/change it would seem to be a very
serious safety issue. That is similar to the PIDA block parameter called CEOPT
which by default value settings puts the PIDA controller in hold when it gets
an error in its MEAS. If the valve opens up so much that it drives the
Measurement high out of range then it holds the last output waiting for the
measurement to come back in range. Hmm, what is wrong with that picture?? At
least, in that case, the operator CAN put the controller in manual and drive it
closed to bring the measurement back in range.
Tom VandeWater
Control Conversions, Inc.
On Jan 27, 2016, at 10:33 AM, Jimmy Chan <jkchan@xxxxxxxxxxxx> wrote:
Hi All,
I believe this is the same issue we discovered back in 2009.
It only happens when you enable HART and does not matter if you have AOUT or
not. When reported to GCS, this is the response we got:
CAR 1013207 -- Function Needed to Ignore Device Malfunction Status Bit
CAR 1013207 which you submitted is being put in REVIEW status, preparatory to
being CLOSED with the following proposed Response:
9 Dec 2009 (RH) - The described problem is Not a Product Defect (NPD) that
can be remedied within the 8.4.1 I/A system, because the I/A logic was
purposely designed to not override basic safety interlocks within its
external devices. With some devices, such as our SRD991 positioner, the
allowable amount of deviation (output setpoint minus actual position) before
the "Device Malfunction" status is set can be programmed/configured by users
in the device itself. The I/A system is purposely designed to never ignore a
Device-Malfunction status bit that is set by the device, even though it may
not be regarded seriously for this one case, because, it indicates any device
malfunction or failure of any sort, some of which could endanger personnel
and the process itself.
We had another go late 2015 with the latest firmware and tried all available
options: NOFAIL, NOALARM OCD, the same results. This is the new case
(1289589) we submitted, as PER this time:
Problem Description : ROUT connected to a HART device should not be frozen
and not having any other means to alter the output when "Device Malfunction"
bit is set.
Suggested Solution: Make this an option, just like with HART
communication failure or at least, make available a method to recover from
the ''hold'' state like switching block to manual before driving the output
manually.
Expected Benefit: Provide more control to user rather than locking the
block in potentially unrecoverable state. For example, if you are trying to
open a damper but it is stuck closed and ''Device Malfunction'' is set. You
should be able to try to close the damper to reset ''Device Malfunction''. As
it is, the output will hold the last value before ''Device
Malfunction'' is set and there is nothing you can do from then on.
Regards
Jimmy Chan | Systems Engineer
Methanex New Zealand Ltd.
409 Main North Road, SH3, Motunui 4383
Private Bag 2011, New Plymouth 4342
T: +64 6 754 9808
E: jkchan@xxxxxxxxxxxx
