Waters 2996, Operator'S Manual

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38 Principles of the 2996 PDA Detector Optics
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4.4.2 Resolution
The data reported by the 2996 Detector to the Millennium
32
database can be the average of
a number of data points. After calculating absorbance, the detector averages absorbance
values based on:
• Spectral resolution
• Sample rate
Averaging Spectral Data Based on Resolution
Spectral resolution (or bandwidth) is the wavelength interval (in nanometers) between
data points in an acquired spectrum. The minimal resolution of the 2996 Detector is
1.2 nm. For example, in 3D mode, the 2996 Detector averages three adjacent diodes for
each reported wavelength when the spectral resolution is set in the Millennium
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software
to 3.6 nm. In 2D mode, absorbance values are computed based on the bandwidth setting.
2D mode is supported in Millennium
32
software versions 4.0 or higher.
Averaging Chromatographic Data Based On Sample Rate
Sample rate is the number of data points per second reported to the Millennium
32
database.
The number of times the photodiodes are read during the sample rate interval is dependent
on the exposure time. For example, if exposure time is 25 msec, and sample rate is 1 sec,
then readings per data point are:
The readings are averaged and reported as a single data point.
Combining Spectral Resolution and Sample Rate
Spectral resolution and sample rate have opposite effects on noise and spectral detail.
Increasing the value of the spectral resolution parameter and decreasing the number of
spectra per second decrease the size of the data file.
Note: The data storage rate is based on wavelength range, spectral resolution, and
sample rate, which are set in the General tab of the 2996 PDA Instrument Method Editor.
For details, refer to the
Millennium
32
Help .
4.4.3 Filtering Data
Use the General tab of the 2996 PDA Instrument Method Editor (for details, refer to the
Millennium
32
Help) to apply an optional noise filter (the Filter Response parameter) to
1000 msec
25 msec
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