Re: [foxboro] HIC's
- From: "Tom VandeWater" <tom@xxxxxxxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Tue, 4 Jun 2002 15:09:52 -0500
Tim,
The following strategy might be too simple but I think it would work
fine.
PIC (PIDA block) -> SWCH #1 (SWCH Block) -> HV#1 (AOUT Block) -> FBM37
or
05 connected to turbine control valve #1
SWCH #2 (SWCH Block) -> HV#2 (AOUT Block) -> FBM37 or 05 connected
to turbine control valve #2
Basically, replace the HIC/PIDA blocks with SWITCH blocks configured as
follows:
SWCH#1&2.INP1 are configured to a value of zero "0"
SWCH#1&2.INP2 are configured to the PIC.OUT
SWCH#1&2.BTIME1 & .BTIME2 are configured to desired value as described
below:
"Balance Time to Input 1 is a real input that specifies the balancing time
for toggling from Input 2 to Input 1. The output approaches the Input1 value
with a response characteristic of a first order lag having a time constant
of BTIME1, in minutes. The value actually input to this parameter represents
nearly one-fifth of the time that it takes the out-put to transfer from the
Input 2 value to the Input 1 value."
HV#1.MEAS is configured to the SWCH#1.OUT
HV#2.MEAS is configured to the SWCH#2.OUT
ALL HV and SWCH blocks are locked in AUTO
SWCH#1 & #2.TOGGLE are set from individual graphical picks that toggle from
0 to 1 or 1 to 0
The graphic representation of HV#1 and HV#2 is set to change color based on
the .TOGGLE for each valve:
TOGGLE = 0 = closed
TOGGLE = 1 = open
The PIC.FBK and .BCALCI can be connected to either SWCH#1.INP2 or
SWCH#2.INP2 parameters It really doesn't matter because they are both
connected to PIC.OUT and the SWCH blocks will always be in AUTO. If you
desire to close all valves you simply put the PIC in Manual and set the .OUT
to zero.
The beauty of this strategy is that it doesn't matter how many HV's you
have or how many are in concurrent use because the PIC will adjust it's
output based on feedback that it gets from it's measurement. When one of
the HV's is removed from service by toggling the .TOGGLE parameter of it's
associated SWCH block, it won't slam it's output to zero but will degrade
based on the value in .BTIME1 of the SWCH block.giving the PIC an
opportunity to control the transition. If there are only two HV's you could
set the .TOGGLE of SWCH#1 from a graphic and connect SWCH#1.TOGGLE.~ to
SWCH#2.TOGGLE. You would then get a simultaneous decrement from the PIC.OUT
value to zero on one valve and a corresponding increment up to the PIC.OUT
value to the other valve. This would not work if you had three or more
valves.
I've never used this strategy but think it will be somewhat better than the
one you currently use. I hope this helps. If nothing else, I bet it
stimulates more discussion.
Tom VandeWater
Dow Corning Corp.
Carrollton, KY, USA
> The HIC#2.MEAS is configured to the HV#2.OUT
> The HIC#2.INITI is configured to the HV#2.INITO
> The HIC#2.BCALCI and .FBK are configured to the HV#2.BCALCO
> The HIC#2.RSP is configured to the PIC.OUT
> The HIC#2.LR is configured to always be in REMOTE
>
> The HV#1.MEAS is configured to the HIC#1.OUT
> The HV#2.MEAS is configured to the HIC#2.OUT
>
> We couldn't figure out how to make the make the M/A transition on the
HIC's
> bumpless, so they aren't. The Console guys just place the HIC that isn't
in
> service in Manual and line up the HIC output with the PIC remote setpoint
> before switching turbines, and then put the newly-in-service turbine HIC
in
> AUTO after the outside guy switches pumps. This is essentially what they
> did on the old board.
>
----- Original Message -----
From: "Lowell, Tim:" <tlowell@xxxxxxxx>
To: <foxboro@xxxxxxxxxxxxx>
Sent: Tuesday, June 04, 2002 12:04 PM
Subject: [foxboro] HIC's
>
> List,
>
> I have a control problem I'm hoping one of you has solved already. This
> refinery of course used to run on board instruments, and we completed a
> cutover to I/A over several years that wrapped up last year. In one of
the
> areas, we have several sets of steam turbine pumps that are alternated in
> service every few weeks. On the old board, there were pressure
controllers
> that were cascaded to HIC's which actually controlled the steam flow to
the
> turbines. To avoid lots of re-designing and Management-of-Change
paperwork,
> we decided to cut these schemes over as faithfully as we could to the
> original design.
>
> The way we ended up configuring these HIC's is as follows:
>
> PIC (PIDA block) -> HIC #1 (PIDA Block) -> HV#1 (AOUT Block) -> FBM37
or
> 05 connected to turbine control valve #1
> ==> HIC#2 (PIDA Block) -> HV#2 (AOUT Block) -> FBM37 or 05 connected
> to turbine control valve #2
>
> The HIC#1.MEAS is configured to the HV#1.OUT
> The HIC#1.INITI is configured to the HV#1.INITO
> The HIC#1.BCALCI and .FBK are configured to the HV#1.BCALCO
> The HIC#1.RSP is configured to the PIC.OUT
> The HIC#1.LR is configured to always be in REMOTE
>
> The HIC#2.MEAS is configured to the HV#2.OUT
> The HIC#2.INITI is configured to the HV#2.INITO
> The HIC#2.BCALCI and .FBK are configured to the HV#2.BCALCO
> The HIC#2.RSP is configured to the PIC.OUT
> The HIC#2.LR is configured to always be in REMOTE
>
> The HV#1.MEAS is configured to the HIC#1.OUT
> The HV#2.MEAS is configured to the HIC#2.OUT
>
> We couldn't figure out how to make the make the M/A transition on the
HIC's
> bumpless, so they aren't. The Console guys just place the HIC that isn't
in
> service in Manual and line up the HIC output with the PIC remote setpoint
> before switching turbines, and then put the newly-in-service turbine HIC
in
> AUTO after the outside guy switches pumps. This is essentially what they
> did on the old board.
>
> What we have been seeing in recent weeks is a weird thing. On one of the
> sets of HIC's, and only one, the HIC.MEAS and HIC.OUT do not match, by
about
> 20% difference, and in fact, the HIC.MEAS and HIC.OUT are constantly
> switching back and forth between the higher and lower value every
> half-second. The valve actually moves up and down in the field, but not
as
> fast as the HIC is trying to move it, so the pressure stays relatively
> stable.
>
> I'm guessing there is some sort of problem with the way we have configured
> this scheme, having to do with the way the HIC.OUT = HV.MEAS and HV.OUT =
> HIC.MEAS such that some sort of bizarre feedback loop has been created.
The
> weird thing is, we have 3 other sets of HIC's configured the same exact
way,
> and they don't exhibit this strange behavior.
>
> Has anybody configured a scheme similar to this? Is there a better way to
> handle this? We need to send a Pressure Controller output as a setpoint
to
> 2 or even 3 different Control Valves, but the valve(s) that isn't in
service
> needs to be able to be controlled manually and shut when it isn't in
> service, and then matched up with the Pressure Controller output before
it's
> put back into service. We don't want to use straight AOUT faceplates,
> because the Console guys aren't used to these, and will get easily
confused
> when they see a different number in the AOUT.MEAS field (which would be
the
> PIC.OUT) than in the AOUT.OUT field (the actual valve output).
>
> Another question is, what the heck is the deal with this HIC? Why is the
> HIC.MEAS and HIC.OUT differing by 20% when they are configured to follow
> each other, and all the other ones like this work fine?
>
> Tim Lowell
> Control Systems Engineer
> Phillips Petroleum Company, Trainer Refinery
> Phone: 610-364-8362
> Fax: 610-364-8211
> tlowell@xxxxxxxx
>
>
>
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>
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