Emerson NGA2000 Reference Manual page 31

NGA2000 Reference
presence of interfering compounds, such as
ammonia added to control NOx emissions.
You must remove these somehow.
After a span, the reading is very erratic...
You have spanned with a gas of much
lower concentration than you think, typically
zero gas or the measuring sample. Trou-
bleshoot the sample system until you are
sure that you are spanning off the real span
gas, and also enter into the analyzer menu
the real span gas concentrations. Enable
limit checking so that this does not happen
again.
The analyzer refuses to span...
If the analyzer considers that it has to
change its span factor by more than the al-
lowed amount, it will refuse to span, if the
calibration limit checking is enabled. Verify
that you have the correct span gas, and its
concentration is correctly entered into the
analyzer. If so, troubleshoot why the ana-
lyzer's span has changed so much.
Rosemount Analytical Inc. A Division of Emerson Process Management
Reference Manual
Possible cause are:
•
Contaminated sample cells in the NDIR
and CLD analyzers
•
Loss of ozone production in the CLD
•
Flame out in the FID
•
Incorrect flame position in the FID
•
Incorrect pressures and flows in all ana-
lyzers
•
Rapid temperature changes (greater
than 10°C per hour change)
•
Temperatures outside specification
•
Foreign substance contamination such
as water carry-over
•
Large ambient pressure changes
•
Sample leaks either within or outside
the analyzer
•
Exhaust back pressure changes
•
Incorrect linearizer coefficients
•
Span gas outside allowable range
748384-C
September 2003
Introduction 1-17