Computing Absorbance Data Points
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4
Averaging Chromatographic Data Based On Sample Rate
Sample rate is the number of data points per second reported to the Millennium
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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 second, 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 996 PDA Instrument Method Editor.
For details, refer to the “Waters 996 PDA Detector Properties” topic in the
Millennium
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Online Help Find tab.
4.4.3 Filtering Data
Use the Channel 1 tab of the 996 PDA Instrument Method Editor (for details, refer to the
“Waters 996 Detector Properties” topic in the
Millennium
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Online Help
Find tab) to apply
an optional noise filter (the Filter Response parameter) to the data sent to the Millennium
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software database. A noise filter of 1 second is the default value, which provides a good
signal-to-noise ratio for most chromatographic separations.
Note the following with regard to filtering data:
• The noise filter is similar in function to an analog RC filter.
• The filter calculates a data point that is a modified rolling average for a wavelength
over a number of readings.
• The filter values are comparable to the effects of a 1-, 2-, or 3-second RC filter.
1000 msec
25 msec
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40
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