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

Setting the gain
The Gain parameter determines how much the detector signal is amplified
electronically, making it larger relative to the level of electronic noise. Amplifying
the signal is helpful when the signal is weak, such as when you use some sampling
accessories. For example, ATR and diffuse reflection accessories typically use a
Gain setting of 2 or 4.
You can let OMNIC automatically adjust the gain to maximize the signal by
setting the Gain parameter to Autogain. For spectrometers other than Mattson and
IR Series models, we recommend using this setting to ensure the best spectral
quality for experiments not involving quantitative analysis.
Note
Set Gain to 1 before performing an automatic alignment. ▲
The actual gain value appears above the Gain text box.
Note
The Gain parameter does not affect detectors used with the optional detector
interface kit. ▲
Specifying the mirror velocity
The Velocity parameter determines the velocity of the moving mirror in the
interferometer. The default value is determined by the detector type and is set
when you select a detector from the Detector drop-down list box.
Using a faster velocity lets you collect more scans in a given amount of time;
however, using a velocity that is faster than the default setting will produce a
noisier signal.
If you are using a sampling accessory with very low throughput, you may find that
you can increase the signal intensity to an adequate level by using a slower
velocity. The results will depend on the detector you are using.
Using a slower velocity increases the time required for an individual scan, but that
does not mean the total measurement time needs to be longer. The stronger signal
obtained (with some detectors) at the slower velocity can allow you to collect
fewer scans, resulting in a shorter measurement time and better quality spectra.
Note
While a wide range of moving mirror velocities is available, some velocity
settings cannot be used for collecting data at certain combinations of spectral
range and resolution (and sample spacing for a Nexus 870 or Magna-IR 860). See
the user’s guide that came with your spectrometer for details. ▲
Setting the aperture size
Use the Aperture parameter to set the size of the aperture opening. The aperture is
a variable-diameter opening which controls the intensity of the infrared radiation
that reaches the sample.
Note
Some systems have a fixed-diameter aperture. On those systems the Aperture
parameter is not available or has no effect on the aperture opening. The rest of this
section applies only to systems with an adjustable aperture. ▲
Using an aperture provides the following advantages:
• It allows the use of more sensitive detectors.
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