Stan,
The I/A Series Historian, a.k.a, the "old" Historian and the "data"
Historian, works as follows:
1) The last two hundred samples are kept in a standard UNIX flat file.
The format is proprietary. These samples were originally used only to
support the recent history option of the trend displays.
2) Samples beyond the first two hundred are kept as extended samples.
The original AP20 had very limited disk space and the ability to keep them
was not considered to be important in the original system design.
3) Reduced data - averages, totals, kurtosis, etc., are kept in
Informix tables. These tables are know as Reduction Groups. The only time
the historian stores values in an Informix table is when the data is reduced
and stored in a Reduction group. It is interesting to note that the sample
data files (1 and 2 above) are not used in the calculation of the reduction
values. Rather, a parallel collection of data is performed using the same OM
lists as the ones we normally associate with the sample data. Data reduction
is relatively expensive - esp. on old boxes - due to the overhead of
inserting the data into Informix.
None numeric data is also stored by the Historian.
1) Process Alarms are stored by the Historian in a circular buffer of
as many as 5000 entries. This buffer is a flat file and there are tools to
dump this file to a flat file, but generally it is pretty useless.
2) Operator Action Journal messages are stored in an Informix table and
the table is treated as a FIFO queue. The size of the queue is configurable.
However, the replacement algorithm is barbaric. When the table fills, an SQL
query is run to delete the oldest 10% of the messages in the table. This
operation can take quite a while - esp. on the older Solaris boxes (50s,
51As, and 51Bs) if the table is sized to its maximum (5000) and the machine
is busy. While the deletion is waiting to complete, the WP is "frozen"
waiting for the operation to complete. This can be quite upsetting to an
operator trying to ramp a setpoint. The only workarounds are: to not use the
table or to limit the size of the OAJ table.
3) System Monitor messages are also stored in an Informix table and
they are treated in the same manner as OAJ entries. However, the delay is
not visible to the operator when the oldest 10% are removed.
Basically, the I/A Series Historian was a pretty poor place to put messages.
FoxAMI provides a much better archive for Process Alarms, Operator Action
Journal Messages, and System Monitor messages. It provides command line and
GUI interfaces for message extraction and presentation.
The next question is going to be, "How do I view the data that my Historian
collects?"
The original answer was, "You can't. The Historian is write only." This
answer did not satisfy most of our customers so we said, "Use the ACE report
writer."
This answer was only minimally better since it could report on only the data
in the Informix tables and most people did not setup reduction groups
because they consumed a large amount of CPU time. Worse yet, the ACE report
writer meant that one had to write a SQL program. It was not a pretty
situation.
A number of options were developed using the Spreadsheets (Prelude and
Lotus) and various reporting tools. Finally, the company released the
'Report Writer 50' as a corporately supported product. This tool can access
Informix based (reduction group) data and live process values, but cannot
access the sample data. Still, it is pretty easy to use and is good for
periodic (shift) reports.
There is also a tool, 'Extract', that allows one to use a GUI to select up
to eight points and pull out the sample or reduction data in a report or to
raise a trend with those points. This tool also has a command line mode that
can be used to extract data for an arbitrarily large number of points.
Hope this helps.
Regards,
Alex Johnson
The Foxboro Company
10707 Haddington
Houston, TX 77043
713.722.2859 (v)
713.722.2700 (sb)
713.932.0222 (f)
[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
-----Original Message-----
From: Stan Brown [SMTP:[EMAIL PROTECTED]]
Sent: Monday, May 01, 2000 9:20 PM
To: [EMAIL PROTECTED]
Subject: Classic historian data location(s)
I am trying to find out where the "classic: historian stores
data. Is
it in the Informix database? Or in the flat files called
samples?
I just located a refernce on bacing up Informix databases,
and I was
wondering if there were other dynamic places that historian
data might
be kept.
--
Stan Brown [EMAIL PROTECTED]
843-745-3154
Charleston SC.
--
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