Spectral Range; Time Constant And Data Rate; Fig. 29 Bandwidth - Knauer Azura DAD 2.1L Benutzerhandbuch

39
Default bandwidth
Response time
Time constant
KNAUER
Optimizing the Detector
For example, a wavelength set at 254 nm with a bandwidth of
4 nm results in an average absorbtion of 252–256 nm.
Fig. 29 Bandwidth
The selection of the bandwidth is a balance between sensitivity
and selectivity. Narrow bandwidths increase selectivity, whereas
broad bandwidths increase sensitivity.
By default (see "Re-Setting the Device" on page 34), the band-
width for the signal wavelength is set to 8 nm and for the refer-
ence wavelength the bandwidth is set to 30 nm.

Spectral Range

When measuring with chromatography software, the spectral
range selected for a given measurement influences the integra-
tion time and consequently the sensitivity of the measurement,
as well as the disk space. The disk space is necessary to save gen-
erated data.
A narrow spectral range increases sensitivity and reduces disk
space. The range, however, should be wide enough to ensure
the detection of all components. Also, the spectral range always
must include the signal wavelength and the reference wave-
length.

Time Constant and Data Rate

The time constant influences the response time of the detector.
The response time determines how quickly the detector
responds to a change in signal. A good rule of thumb for selec-
tion of the detector time constant is that it should be no larger
1
than of the baseline peak width of the first peak of interest
------
10
(in seconds). Increasing the time constant allows more averag-
ing of the signal (also known as digital filtering) and results in
less baseline noise (see figure 30). However, increasing the time
constant too much may result in broad peaks, reduced peak
heights and asymmetric peak shapes. Therefore, a compromise
has to be found.
In general, the best time constant is the reciprocal of the data
rate. If increased sensitivity is desired, or if the baseline noise is
DAD 6.1L, DAD 2.1L, MWD 2.1L User Manual V6700, Version 1.0