Re: [foxboro] CP60 Sizing
- From: Terry Doucet <doucet427@xxxxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Wed, 21 Apr 2010 14:24:44 -0400
Donato,
One would expect that 100% - idle time = CP load but this is not always the
case with the CP station block. I would suggest that you monitor CPLOAD,
fieldbus load and the accumulated overruns and ignore idle time as it is often
meaningless. These numbers can be historized to give you long term information.
I would also monitor the OM parameters from the Station display.
If you get overruns, then your CP is overloaded. Howmany overruns you get per
day gives you an idea of how often you are overloaded. You want zero overruns.
Any overruns can give errors in ACCUM blocks and CALC timing functions.
Foxboro EDOC has an Excel spreadsheet for the CP60 loading. If you do not have
any sequence blocks, you should be able to get the Excel spreadsheet to match
your existing CP60 load and fieldbus load. You can then transfer this data to
the newer CP270 Excel spreadsheet and get a very good idea of what the existing
loading would be on a new CP270. I suspect that you could ask that this be done
by Invensys / Foxboro as part of any quotation for an Upgrade.
I believe that Foxboro recommends that total CPLOAD is less than 80 and total
FB scan is less than 60.
If you have sequence blocks then loading gets very complicated since lines of
sequence code processed per block period can vary with the logic and it is
tough to assign a value in the Excel spreadsheet for this logic. If you have a
lot of sequence blocks you likely need assistance from a Foxboro expert.
Terry
> I am proposing a migration to a Preferred platform of I/A. We
> currently have I/A 7.1.1 with CP60 controllers. I would like to base
> my proposal on two arguments:
>
> 1) Processor idle time is 30% and there are possible additions on the
> way. Are there recommendations as to how little idle time is too
> little?
>
> Donato Azevedo
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