Re: [foxboro] Foxboro field bus access errors
- From: "Dirk Pauwels" <dirkpauwels_1@xxxxxxxxxxx>
- To: foxboro@xxxxxxxxxxxxx
- Date: Mon, 12 Sep 2005 09:08:45 +0000
We have exactly this problem on our CP60's. Lots of noise interference which
causes multiple bus errors and therefore a lot of bus switching. According
to Foxboro this is due to our coax connection. We've done everything
possible (except FO) to decrease the noise,(implemented the advise from
Invensys) but still the problem remains. Strangly enough it was Foxboro who
advised to change from twinax to coax when we upgraded from CP40 to CP60...
I'm trying to find the budget to change to fibre optic, but it's difficult
to defend such an expense when at first view (for management) everything
seems to be normal. It would have been easier to get the budget when we did
the upgrade to CP60.
Rgds,
Dirk Pauwels - DCS coordinator
Engineering dept.
Hexion Specialty Chemicals
E mail: dirk.pauwels@xxxxxxxxxxxxxx
T. +32.(0)3.570.95.97
F. +32.(0)3.570.16.09
Mob. +32.(0)497.428.300
>From: <tom.vandewater@xxxxxxxxxxxxxx>
>Reply-To: foxboro@xxxxxxxxxxxxx
>To: <foxboro@xxxxxxxxxxxxx>
>Subject: [foxboro] Foxboro field bus access errors
>Date: Fri, 9 Sep 2005 15:12:16 -0400
>
>List, I received the following off-list from someone that wishes to
>remain anonymous. I thought it might be of some value. I found it
>informative!
>Tom,
>I read your message on Cassandra regarding PIO Bus access errors.
>
>If you have 100 series FBM's running on a CP60, then I would think that
>there was a strong likelhood that you upgraded from CP10 or CP30A/B or
>CP40A/B. The 10, 30 and 40 ran a serial fieldbus that started at about
>22V p-p. If you had noise around at 200 -600 mV, the electronics could
>handle the signal to noise ratio and you were OK.
>
>When the CP60 was first introduced, it ignored communication errors.
>Foxboro let the hardware failure take care of SMDH alarms. But the CP60
>fieldbus runs Ethernet that starts at 2 V p-p and now the electronics
>has difficulties when noise of 200 - 600 mV hits the wires. A later
>version of CP60 actually looked at the communication errors, but then
>the famous PIO bus access errors started to hit the CP60 client base.
>
>The above has been discussed on Cassandra, many times.
>
>There are some Ethernet rules supported by bodies like ISA (see their
>Ethernet book) that I have never seen in Foxboro documentation. One
>states that for 802.3 ethernet, co-ax cable should never run outside one
>rack, in an industrial area. It does not provide enough noise immunity.
>Based on the number of Quick Fixes that got released on the CP60 and the
>FCM's and DCM's, Foxboro made many attempts to try and massage the code
>to intelligently work around the basic signal to noise ratio, but there
>is only so much that can be done until one deals with that ratio and
>tries to increase it (get rid of the noise) for 24 hours a day, 7 * 365!
>
>Foxboro provides help in trying to suppress noise on the CP60. If your
>field service rep has been in and has done all the recommended action,
>it may be time for you to consider fibre and splitting fieldbuses with
>as many FCM's as you can. Remember that with 100 series FBM's and a
>single FCM or DCM, the CP60 fieldbus is actually less "powerful" than a
>CP40A fieldbus where the cpu had no RAM error detection and correction
>code. The CP60's power only comes with multiple FCM's or DCM's.
>
>I doubt that any of the above will help with your problem because you
>have a running plant that likely goes for 5-6 years between planned
>shutdowns but it may provide some help to know why this is happening.
>
>
>
>
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