Re: [foxboro] FCP vs. ZCP? (forked from: network storm)

  • From: "Badura, Tom" <tbadura@xxxxxxxxxx>
  • To: <foxboro@xxxxxxxxxxxxx>
  • Date: Thu, 12 Feb 2009 17:56:04 -0600

Please pardon my ignorance René, but what are UCM's.  You have pointed out some 
very valuable information, but I am not sure if I followed it fully.  It sounds 
like the jest is that you can reduce I/O loading on ZCPs by increasing the 
number of FCM (pairs) thus reducing the number of FBMs on each pair. Is there 
then some configuration to be down to level the load in the ZCP? (similar to 
phasing in the control scan cycle?).  We have been going merrily along with the 
assumption that the most cost effective use of equipment was to "load up" each 
FCM pair with its max. I/O modules (30 each); however, sounds like there may be 
some other things to consider.

Thanks for the great info,


Tom Badura
Plastics Engineering Company
920-458-2121 x3366
tbadura@xxxxxxxxxx




-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx] On 
Behalf Of Bakker, René
Sent: Thursday, February 12, 2009 4:38 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] FCP vs. ZCP? (forked from: network storm)

Sorry Glen, with all respect but I, in turn, don't agree with you.

Especially if DCM's are involved, one should take care migrating to FCP270.
Fact is that the use of DCM's behind a CP60 allowed you to bring the I/O load 
down substantially.
An identical issue plays a role when using 270 series CP's.
The FCP270 does not allow the leveling of its I/O load by using FCM's (=270 
equivalent of DCM's). The ZCP270, however, does!
Be aware that when applying a FCP270, the I/O load caused by the communication 
with the total of the connected I/O, regardless of the type (FBM100 series, 
FBM200 series, migrated Foxboro Spectrum or competitor stuff or any 
combination) just adds up and defines the total I/O load. There is NO way of 
leveling that I/O load when using FCP270 and we, Invensys, state clearly that 
the buck stops at an I/O load of 70 percent.
However, when using ZCP270's connected to your FBM's of whatever kind, you CAN 
level the I/O load, simply by applying (enough) FCM(pair)s.
Example: you intend to replace 30, 40 or 60 series CP's connected to migrated 
Foxboro UCM's by 270 CP's.
Applying FCP's would force you to stick to 2 UCM's per FCP270 (assuming there 
are 60 I/O cards to be scanned at 0.5 second rate). Reason being that you 
otherwise exceed the 70 percent I/O load (and will end up with a block 
processor load that is likely to stay below 10 percent. How is that for a 
waste?)
Applying ZCP270's will allow you to go to a significantly higher number of 
UCM's, assuming you apply enough FCM's.
Basic rule is as follows: Apart from a small (2 to 4 percent) overhead per FCM 
(pair), the total I/O load imposed on a ZCP270, equals the I/O load for the FCM 
with the highest FBM I/O load, regardless of the number of FCM(pair)s 
connected!!, nothing more!! (be aware: the max no. of allowed FCM(pair)s is 32)
When using FCP270, the I/O load can't be spread because there are no FCM's or 
equivalents that you can use or apply. That means that the FCP270 gets the 
total accumulated I/O load.
In practice this means that you can connect two fully loaded (total 60 I/O 
cards) UCM's to a FCP270 while you can easily connect 4 or more fully loaded 
UCM's to a ZCP270, assuming you apply enough FCM(pair)s.
If it is a wise decision to put that many UCM's behind one and the same CP is a 
different story. I would say that such depends completely on how your plant as 
well as control strategy is built and defined.
So, to make a long story short: before deciding on which of the two new CP270 
types to apply, you should have a long and detailed discussion with your 
Invensys sales rep and don't leave your local service man/woman out. Together 
you will certainly be able to come to the best solution. One thing is for sure: 
it is NOT a black and white story. As always, there are far more sides to the 
medal than visible at first glance.
And, if all else fails (which I doubt), contact the TAC group in your area for 
details on such an important decision. That is what we are here for.
Succes and best regards,
René Bakker - Invensys EMEATAC - Baarn - the Netherlands

 
 
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