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Instruction Manual
748332-F
April 2003
Rosemount Analytical Inc. A Division of Emerson Process Management Maintenance and Troubleshooting 4-11
Model NGA2000 NDIR
4-14 MODULATION CHECK
The modulation check is a measure of the
energy absorption capacity of a gas mixture,
where total absorbency is 100% modulation
and zero absorbency is 0% modulation. The
modulation check can be used as a tool for
tracking the sensitivity of the Analyzer Module
and for discovering potential detector/source
problems.
To perform a modulation check, do the
following:
Access the Primary Variable Parameters
menu.
Select Modulation Check.
Follow the Instructions and Then line
commands, which are the following:
Flow zero gas, press START softkey and wait.
Flow span gas when prompted, press START
softkey and wait.
When the Instructions line again prompts the
user to flow zero gas, the modulation check is
finished.
Note the value on the Percent Modulation line.
Find the Percent Modulation value on the
Data Sheet in the rear of this manual. Some
standard Analyzer Modules will not have a
value. If a value is present, compare this to
the new value.
If 100% span gas was used during the
modulation check, the new value should be
within ±10% of value on the Data Sheet. If it is
out of this range, call the factory for further
interpretation. If modulation checks are used
for trending, variance from check to check
should not exceed ±20% per month.