Which Bus are you running on??
With 100 series fieldbus, active bus constantly used....secondary bus gets
touched twice a minute for health.
Something wrong with that oscilloscope analysis
If the CP was not actually communicating with the FBM's for that period of time
they would be going into Failsafe and being reflected in many places in the
system.
The FBM's would be getting marked bad after missing 3 successive BPC scan passes
Also the sysmon messages would be reporting if the fieldbus is switching
between A and B
Above set to defaults would be 10 seconds for Failsafe
1.5 seconds for FBM error messages..(.5 BPC)
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx] On ;
Behalf Of John Pilman
Sent: Friday, September 30, 2016 10:10 AM
To: foxboro@xxxxxxxxxxxxx
Subject: [foxboro] Odd Fieldbus behavior
We recently found a Fieldbus which quits communicating for about 25 seconds
each minute without generating a fieldbus error. Now we wonder if this is
normal behavior, or if there is some other explanation. We will be trying to
reproduce this behavior in the shop, but it may take some time to set up that
test. Have any of you seen this before?
We went to a customer's site to troubleshoot the fieldbus because there are
occasional fieldbus errors reported on the system monitor. This site has a
fault tolerant FCP270 pair and a number of Series 100 FBMs. They are
experiencing errors which appear on the system monitor as fieldbus B failures
approximately once per day. During the investigation, using an oscilloscope,
we observed that the activity on fieldbus A was stopping approximately 25
seconds each minute. Fieldbus A does show some errors, but far fewer than bus B.
Here is a still image of the oscilloscope trend of the voltage on both busses
(file size 225 KB).
https://drive.google.com/file/d/0B4-fZtD9qOhIQWVmYmlUalhjaEU/view?usp=sharing
This image clearly shows that one bus ceases activity. The time that the red
trace was idle was approximately 24 seconds.
Note: The Y scales (voltage) appear to have different ranges. That is strictly
an anomaly of the scope settings and the different probe impedances at the time
these measurements were taken. Please don't let that interfere with your
interpretation of the bus activity.
Here is a video of the oscilloscope with probes on both busses (97.3 MB).
https://drive.google.com/open?id=0B4-fZtD9qOhIMG9MdThXZUw4bW8
The scope's time stamp can be seen in the upper right hand corner. The blue
trace shows normal activity on bus B throughout the video. The red trace, bus
A, activity stops at 13:22:38 and resumes at 13:23:04.
Here is a video of the oscilloscope with a probe on A bus only (117 MB).
https://drive.google.com/open?id=0B4-fZtD9qOhIdW1Qc2pJNVllWWM
The bus activity is consistent until 11:01:01, when it stops. It then resumes
at 11:01:26.
Thanks
...John
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