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Dionex VWD Operator's Manual
3.5.1
Time Constant
The time constant is a measure of how quickly the detector responds to a
change in signal. The time constant can be set to any value between 0.00
and 4.55 seconds. The selected time constant applies to all UV-Vis data
collected.
Select a time constant that is about 10% of the peak width at half-height
for the narrowest peak of interest. A longer time constant allows more
averaging of the signal and results in less short-term noise. However, a
time constant that is too long may result in reduced peak heights and
asymmetric peak shapes. When set correctly, the time constant
significantly reduces baseline noise, but reduces peak height only slightly.
The Chromeleon 7 Instrument Method Wizard or Chromeleon 6.8
Program Wizard will automatically calculate the time constant (and data
collection rate), based on the value you enter for peak width at half-height
on the Channels page (in Chromeleon 7) or the UV Options page (in
Chromeleon 6.8).
3.5.2
Data Collection Rate
The data collection rate is the number of data points per second (Hz) that
Chromeleon collects from the detector and stores as raw data. The
number of data points per second generated by the detector electronics
depends on the detector version. The single-channel Dionex VWD
generates data at 10.0 Hz; the four-channel Dionex VWD generates data
at 100.0 Hz.
The Dionex VWD data collection rate can be set to between 0.2 and
10.0 Hz (for a single-channel Dionex VWD) or 0.2 and 100.0 Hz (for a
four-channel Dionex VWD).
•
In general, each peak should be defined by at least 20 data points. For
chromatograms with co-eluting peaks or low signal-to-noise ratios,
40 data points per peak is recommended.
•
If all peaks are relatively wide, select a slower data collection rate
(1.0 Hz, for example).
•
If any peaks of interest are less than a few seconds wide, select a
faster data collection rate (10.0 Hz, for example).
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