Re: [foxboro] Clearing Accum block
- From: "Johnson, Alex P (IPS)" <alex.johnson@xxxxxxxxxxxxxxxx>
- To: foxboro@xxxxxxxxxxxxx
- Date: Thu, 20 Oct 2005 11:35:23 -0400
According to the block documentation for the ACCUM block, the CLEAR =
(reset)
input works as follows:
CLEAR=20
Clear is a Boolean input that sets the accumulator output to zero =
when
CLEAR makes a zero-to-one transition. The ACCUM block automatically
clamps this input at zero if no connection exists.
Since it works on the rising edge, the reset would occur 1 minute after =
the
top of the hour. That is, at 10:01 not 10:00 the ACCUM block would be =
reset.
This approach will reset the accumulator every hour, but not at the top =
of
the hour.
The three ways that I know to do it at the top of the hour are:
1) Connect it to a CALC output
2) Write an IND block to set it using an external reference
3) Write a script on an AW to reset it.
The problem with the first approach is that one would not be able to =
manual
reset it from the ACCUM faceplate. The CLEAR parameter would be secured =
to
the CALC output. Sometimes this is an issue.
The problem with the second approach is that you have to write a =
sequence
block, but the CLEAR parameter would not be secured and the =
implementation
is not fault tolerant.
The problems with the last approach are:
1) If the AW is down, the reset will not occur.=20
2) One might forget about the script during an upgrade and not =
reschedule
it.
3) One-shots across the Nodebus can eventually get expensive.
Me? I'd use the sequence block unless I knew that a manual reset would =
not
be needed.
Hope this is useful.
Regards,
=20
Alex Johnson
Invensys Systems, Inc.
10707 Haddington
Houston, TX 77063
+1 713 722 2859 (voice)
+1 713 932 0222 (fax)
+1 713 722 2700 (switchboard)
alex.johnson@xxxxxxxxxxxxxxxx
=20
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx =
[mailto:foxboro-bounce@xxxxxxxxxxxxx] On
Behalf Of "Perrot, Fran=E7ois"
Sent: Thursday, October 20, 2005 3:56 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] Clearing Accum block
Brian,
An idea is to make the following connection on the reset param:
CPxxxx_STA:STATION.MINUTE.~X0000 where CPxxxx is the name of the CP =
which
contents the ACCUM block.
Each time the minute is equal to zero (Once per hour) it will reset the
accum
Regards
F.PERROT
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx =
[mailto:foxboro-bounce@xxxxxxxxxxxxx] On
Behalf Of BrianLong
Sent: jeudi 20 octobre 2005 14:32
To: Foxboro
Subject: [foxboro] Clearing Accum block
There are a number of ways to do this but I though someone out there =
might
have a "better or clever" way. I need to clear an ACCUM block at the =
top of
every hour.
Thanks in Advance,
Brian Long
Arkansas Kraft
=20
=20
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This mailing list is neither sponsored nor endorsed by Invensys Process
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