Replacing the lamp
4-17
The Waters 2489 Detector uses a combination of front-end electronics and
lamp optimization software that makes the best use of the energy present to
optimize instrument performance. The design also compensates for the lamp
energy changes that occur across the deuterium spectrum as well as lamp
aging. These enhancements allow the detector to 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 it is powered up or
when the Calibrate key is selected. One of these steps is the lamp optimization
software routine. After the unit has verified the calibration of the
monochromator, the instrument evaluates energy levels in a number of
characteristic regions across the spectrum. The integration time of the
front-end electronics is adjusted to maximize the signal within these regions.
The intent is to maintain a high signal-to-noise ratio and operate with a clean
signal. In this way, the instrument’s sensitivity to lamp energy is virtually
eliminated as a major contributor to performance.
When operating the detector, regularly invoke the lamp optimization software
routine to maintain performance. Waters recommends that the detector be
cycled off and on or the Calibrate key be selected at least once a week.
Eventually, the lamp’s signal becomes low enough that replacement is
necessary. You should replace the lamp when the energy value drops below 15
nanoamps (nA). This value corresponds to the cut off used in the detector’s
diagnostic tests. You should set a higher energy value to avoid dropping below
this value during an analysis.
Ultimately, the detector’s performance is a function of the user’s unique
application. Noise and drift measurements are appropriate for evaluating
performance and setting the boundaries for acceptable sensitivity limits. The
detector’s on-board diagnostic tests allow lamp usage to be recorded and the
lamp serial number to be reported. You can replace lamps at any time that is
appropriate to your method.
When to replace the lamp
Rule:
Always run the Change Lamp diagnostic test after you install a new
Summary of Contents for 2489
Page 8: ...viii...
Page 32: ...1 16 Theory and Principles of Operation...
Page 134: ...3 66 Preparing the Detector...
Page 193: ...Warnings that apply to all Waters instruments A 9...
Page 204: ...B 6 Detector Specifications...
Page 220: ...D 14 Solvent Considerations...
