Waters 2489, Overview And Maintenance Manual

Page: 104 / 150

June 11, 2015, 715004752 Rev. A
Page 104
This section describes the procedure for removing and replacing the detector
deuterium lamp.
4.5.1 Lamp characteristics
The intensity of the deuterium source lamp varies by wavelength, as shown in the
figure below.
Figure 4–4: Deuterium lamp sample beam intensity profile
4.5.2 Lamp energy and performance
As the lamps used in traditional detectors age, the signal-to-noise performance of the
instruments degrade. Determining the longevity of useful lamp life can be difficult
because of varying user requirements and individual lamp behavior.
The detector’s design also compensates for the lamp energy changes that occur
across the deuterium spectrum as well as lamp aging. Thus the detector can operate
at the same, high signal-to-noise performance at longer wavelengths of the visible
range without the use of a second lamp, such as tungsten.
The detector performs several self-diagnostic tests when powered-on or when the
Calibrate key is selected. One of these tests is the lamp optimization software routine.
After the detector verifies the calibration of the monochromator, it evaluates energy
levels in several characteristic regions across the spectrum. The integration time of
the front-end electronics is adjusted to maximize the signal within these regions. The
effect is to maintain a high signal-to-noise ratio and operate with a clean signal.
When operating the detector, run the lamp optimization software routine at least once
a week.
Eventually, the lamp’s signal becomes low enough that replacement becomes
necessary. You should replace the lamp when the energy value approaches 15
nanoamps (nA), which corresponds to the cutoff adopted in the detector’s diagnostic
tests. Ultimately, however, the detector’s performance is a function of its application
so replace lamps whenever you determine doing so is appropriate for your method.
Inte
n
sity
Wavelength (nm) 190 700