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Theory of Operation
Firmware Description
stored in the wavelength calibration table in an EEPROM
(electrically-erasable PROM) which is part of the spectrograph
electronics. During each start-up of the spectrophotometer, each discrete
wavelength value is assigned to a photodiode of the array.
• Recalibration of the wavelength scale can be performed to compensate for
minor deviations from initial production conditions. Recalibration is
achieved using the deuterium line data, that is, the exactly-known
positions of the deuterium emission lines at 486.0 nm and 656.1 nm.
Because of the real-pass band function of the spectrophotometer, which is
different from the theoretical one, the maximum positions of the two
emission lines cannot be used. Instead the line centroids are used for the
calibration/recalibration process. A description of this method is given in
section Wavelength Calibration in Appendix A of NBS Publication 260-66
from NIST (National Institute of Standards and Technology). For the
address of NIST, see “Source of Standards” on page 14.
Upon request of the operator through the user interface of the software
the new parameters are used together with the wavelength calibration
table to calculate a table of correction coefficients which are applied to
each spectrum.
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