Thermonicolet Omnic Software User's Guide 6.1 (PDF) - Charles E ...

Specify the sensitivity for this check by using the scroll bar. The sensitivity value
indicates how readily the check finds and reports signs of detector icing. If you
use a low value, these signs will be found only if they are large; if you use a high
value, these signs will be found even if they are small. The current setting appears
below the scroll bar, between the minimum and maximum values.
Checking the background
for carbon dioxide or water
Turn on CO2 Levels in the background checks if you want collected background
spectra to be checked for carbon dioxide absorptions that exceed a specified level.
Turn on H2O Levels to check the background spectra for water absorptions. This
is a routine check that you should normally leave turned on.
A spectrometer is normally purged or has a sealed and desiccated optics
compartment to minimize the amount of carbon dioxide and water vapor inside it.
If the carbon dioxide or water vapor levels are too high, absorptions of infrared
energy by the gases will result in unwanted peaks in the background spectrum.
This in turn can affect the ratioing of sample spectra, producing spectral features
not due to the samples.
Use the scroll bars to specify the sensitivity for these checks. The sensitivity value
indicates how readily the check finds and reports carbon dioxide or water
absorptions. If you use a low value, these absorptions will be found only if they are
large; if you use a high value, they will be found even if they are small. The current
setting appears below the scroll bar, between the minimum and maximum values.
Checking
the background
for an accessory
Checking the
interferogram amplitude
Turn on Background Correct For Accessory in the background checks if you want
the software to check the appropriateness of the current background for an
accessory. This is a routine check that you should normally leave turned on.
The ratioing of sample spectra collected with accessories requires that a
background spectrum be collected under special conditions or using an
appropriate background material. In general, you should collect the background
using the settings used to collect sample spectra and using the sample holder (if
one is used for samples) without the sample installed. See “Collecting a
background spectrum” for more information.
Turn on Peak Amplitude Within Range in the interferogram checks if you want the
maximum amplitude of collected interferograms checked. The maximum amplitude
is the absolute value of the largest interferogram peak (the peak can be positive or
negative). This is a routine check that you should leave turned on unless the sample
peaks are extremely small and you are collecting a large number of scans.
Type in the Interferogram Minimum and Interferogram Maximum text boxes the
limits within which you want the maximum amplitude to fall.
Note
For the purposes of this check the interferogram amplitude is automatically
normalized to a gain value of 1 to compensate for changes that can occur at
different actual gain settings. ▲
Comparing the
interferogram amplitude
with the noise level
Turn on Minimum Peak Above Noise in the interferogram checks if you want the
software to check to make sure the peak-to-peak amplitude of collected
interferograms is greater than the specified peak-to-peak noise level. (The peak-topeak
amplitude of the interferogram is obtained by subtracting the actual intensity
value of the largest negative peak from the intensity value of the largest positive
peak.) This is a routine check that you should leave turned on unless the sample
peaks are extremely small and you are collecting a large number of scans.
OMNIC User’s Guide 135