Re: [foxboro] Clearing Accum block
- From: "Doucet, Terrence" <tdoucet@xxxxxxxxxxxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Thu, 20 Oct 2005 11:48:08 -0400
Alex,
Your second approach (IND block with Ext. Ref) you describe
the implementation not being fault tolerant. Can you explain why?
Are not the ACCUM and the IND in the same (FT) CP?
Thanks,
Terry
-----Message d'origine-----
De=A0: foxboro-bounce@xxxxxxxxxxxxx =
[mailto:foxboro-bounce@xxxxxxxxxxxxx] De la part de Johnson, Alex P =
(IPS)
Envoy=E9=A0: October 20, 2005 11:35 AM
=C0=A0: foxboro@xxxxxxxxxxxxx
Objet=A0: Re: [foxboro] Clearing Accum block
According to the block documentation for the ACCUM block, the CLEAR =3D
(reset)
input works as follows:
CLEAR=3D20
Clear is a Boolean input that sets the accumulator output to zero =3D
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 =
=3D
the
top of the hour. That is, at 10:01 not 10:00 the ACCUM block would be =
=3D
reset.
This approach will reset the accumulator every hour, but not at the top =
=3D
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 =3D
manual
reset it from the ACCUM faceplate. The CLEAR parameter would be secured =
=3D
to
the CALC output. Sometimes this is an issue.
The problem with the second approach is that you have to write a =3D
sequence
block, but the CLEAR parameter would not be secured and the =3D
implementation
is not fault tolerant.
The problems with the last approach are:
1) If the AW is down, the reset will not occur.=3D20
2) One might forget about the script during an upgrade and not =3D
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 =
=3D
not
be needed.
Hope this is useful.
Regards,
=3D20
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
=3D20
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx =3D
[mailto:foxboro-bounce@xxxxxxxxxxxxx] On
Behalf Of "Perrot, Fran=3DE7ois"
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 =3D
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 =3D
[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 =3D
might
have a "better or clever" way. I need to clear an ACCUM block at the =
=3D
top of
every hour.
Thanks in Advance,
Brian Long
Arkansas Kraft
=3D20
=3D20
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