Hitachi CHROMASTER 5160 Instruction Manual page 278

2.4 Principle of Operation
And, for measurement in the D2&W lamp mode, filter F (UV-32)
is inserted in the optical path within 351 to 400 nm, and filter F
(O-54) is inserted in the optical path within 601 to 900 nm in
order to cut off the second-order diffraction light.
About 2-wavelength Measurement Mode:
Aberration-free concave grating G1 is reciprocated at a high
speed between any 2 wavelength positions. Signals at the
two wavelengths after beam dispersion are detected
alternately and data is processed at each wavelength.
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