Reference Manual
748384-C
September 2003
1-34 Introduction
Rosemount Analytical Inc. A Division of Emerson Process Management
NGA2000 Reference
1-18 ANALYZER INTERNAL DATA STORAGE
Analyzers store up to 24 hours of averaged data
in their volatile memory. It is stored as 96 fif-
teen-minute averages. You can select which
two variables out of a list of about 20 are stored.
The analyzer validity, and calibration status, as
well as the time of each segment are stored.
This data can be retrieved using a computer in-
terface. It is not available through the menus.
It is intended for certain CEMS monitoring re-
quirements where data must be reported to a
monitoring authority, and absence of data due
to, for example a fault in the monitoring com-
puter will cause significant monetary cost.
NOTE
The data is volatile!
If you lose power, the data is lost. However
if the analyzer power stays on, the data re-
mains despite network upsets and anything
else that happens.
a. Basic
Instructions
Select Technical level configuration...
Select Diagnostics menus...
Select Analyzer module diagnostics...
Select Trend display control...
Select the desired parameters to store.
Setup a computer with a suitable LON inter-
face.
Using the DDE server program and an ap-
plication such as Excel, use a macro or
program to interrogate the analyzer.
It will take a few minutes to download all the
data.
b. Details
The data is stored in an array inside the
analyzer memory. The data may be re-
trieved by the use of two specific variables,
DATA_INDEX and DATA_POINT.
You set DATA_INDEX to refer to a particu-
lar data point, wait for about one second,
and then read DATA_POINT.
Both these variables are arrays, whose
elements refer to specific things. See the
variables appendix for details.
The Excel example spreadsheet called
NGATREND.XLS shows how to do this in
the Visual Basic for Applications language.
If the analyzer has not been powered for the
full 24 hours, the unused sets of data will be
filled with large negative numbers. This is
so that it will be obvious that the data is not
correct.
The analyzer puts the data into the appro-
priate time slot. If its internal clock is not
corrected by a platform, this may be wrong.
However the analyzer will store the time for
each data point along with the data, so you
can see which data is which. The data is
retrieved point by point, so that you have to
be aware when the day has rolled over.
Network variables: DATA_POINT,
DATA_INDEX