Waters 2475, Operator'S Manual, Page: 28 / 228

1-14 Theory of Operation
• Lamp power supply – Provides stable xenon lamp operation.
• DC power supply – Provides voltage for the analog and digital circuitry.
It is the DC power source for the detector.
Wavelength verification and test
The xenon arc lamp and the integral erbium filter exhibit peaks in the
transmission spectrum at known wavelengths. Upon startup, the detector
waits 5 minutes for the xenon lamp to warm and stabilize. The detector
verifies calibration by comparing the locations of these peaks with calibration
data stored in memory. If the results of this verification differ from the stored
calibration by more than
±
2.0 nm, the detector displays a wavelength
verification failure message. This message indicates a manual wavelength
calibration is necessary. The detector verifies, rather than recalibrates, to
avoid errors that can occur if the flow cell contains residual materials.
Calibration requires a clean flow cell and transparent mobile phase. You can
initiate a manual wavelength calibration anytime to replace the previous
calibration data with new data.
Tip:
The combined wavelength accuracy specification of the detector is
±3.0 nm, but the wavelength accuracy of each grating is held to ±2.0 nm.
When the detector runs continuously, you should perform wavelength
verification weekly by turning it off and then on again, or perform the
calibrate wavelength function through the console. The verification tests
require 5 minutes of lamp warmup time to stabilize the lamp.
Operational modes
The detector operates in single or multichannel mode, allows spectrum
scanning using a flow cell, and provides Difference and MaxPlot functions.
Single-channel mode
The detector defaults to single-channel mode, monitoring a single channel for
an excitation/emission wavelength pair. You can specify the excitation
wavelength between 200 and 890 nm on channel A.
In single-channel mode, the detector automatically engages the second-order
filter for excitation wavelengths of 400 nm and longer and removes it for
wavelengths shorter than 399 nm. The second-order filter is an optical filter