Re: [foxboro] Timer Question
- From: "Johnson, Alex P \(IPS\)" <alex.johnson@xxxxxxxxxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Fri, 12 Oct 2007 11:18:10 -0400
Re: If memory serves, Alex Johnson had some tips some time ago on this
list
for "tuning" the fieldbus by changing the order that segments were
scanned depending on the scan times for those segments.
The FCM/DCMs are scanned in the order shown in <cpLbug>_ECB.
In general, you want the FCM with the fewest FBMs to be listed first.
The CP issues all data requests in that order and then goes to the each
one in that order to pickup the requested data.
Each FCM processes in parallel so by putting them in increasing chain
length you maximize the probability that the FCM will have the data when
CP comes back to request it.
Make sense?
Regards,
Alex Johnson
Invensys Systems, Inc.
10900 Equity Drive
Houston, TX 77041
713.329.8472 (voice)
713.329.1700 (fax)
713.329.1600 (switchboard)
alex.johnson@xxxxxxxxxxxxxxxx
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
On Behalf Of Kevin Fitzgerrell
Sent: Thursday, October 11, 2007 6:48 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] Timer Question
Matt,
Just a couple more comments:
Station idle time includes idle time in overrun cycles, which means
once your CP starts overrunning, idle time is not a good indication of
CP load. In fact, it is a good indication of how inefficient the CP
is when overrunning. When the CP can't finish it's processing in a
BPC, it schedules an extra cycle to finish the processing in. That's
the overrun cycle. Your timer blocks should be processing fine,
however the extra overrun cycles aren't accounted for in the timer
block algorithm with would account for your inaccurate timing.
How many FBMs to these CPs have? Are they using 100 series FBMs? If
so, how many 100 series FBMs are on each pair of DCM10E modules? Do
you have any Intellegent Transmitter FBMs? Do you have any digital
bus FBMs (223 or 224)?
Most of my experience with high I/O scans has been with 100 series
FBMs where not enough DCM10Es had been specified. Once extra DCMs
were added to split the load better our I/O scans went way down.
Intellegent Transmitter FBMs seem to be an unusually high load on the
fieldbus - I ended up replacing a couple in one plant area (with
FBM01s) which made a huge difference in I/O scans.
If memory serves, Alex Johnson had some tips some time ago on this
list for "tuning" the fieldbus by changing the order that segments
were scanned depending on the scan times for those segments.
Regards,
Kevin FitzGerrell
On 10/12/07, Gunter, Matt <Matt.Gunter@xxxxxxx> wrote:
> MeeOuch! As Spencer Katt of eWeek would say!
>
> Thanks to everyone for their comments.
>
> We are running CP60s and I have suspected loading. Here's the skinny
> ...
>
> CP Field Bus Scan Cont Blks Seq Blks Total
> Station Idle
> Good Timer CP 61.4 13.4 3.2 78.0
> 62.9
> Bad Timer CP 1 121.2 15.8 7.6 144.6
> 77.6
> Bad Timer CP 2 114.8 13.0 6.0 133.8
> 80.4
>
> When I check the loading in our lab, the field bus scan is zero - of
> course since it is not hooked to any real hardware.
>
> Apparently the higher station idle time is not indicative of resources
> available to process timer blocks. It appears that I am going to have
> to figure out a way to reduce field bus scanning.
>
> Best Regards
>
> Matt Gunter
> ATK Launch Systems
=
=
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