228-90095F
7
Chapter 2 Specifications
Please read a see instruction manual.
Chapter 3 Measurement systems
3.1 Optical system
Figure 3.1 illustrates the instrument’s optical system. It is equipped with a D2
lamp and W lamp (model 20AV) for the light source. The angle of mirror M1 is
used to choose between the two light sources. The angle of mirror M1 is switched
by the “LAMP” setting under the function key (operation controls). When the
mirror M1 position is switched, the lamp switching photomicrosensor detects the
angle of mirror M1, so only the selected light source stays on and the other lamp
turns off. In addition, if “LAMP” is set to “3”, then it is possible to select both
lamps. Model 20AV uses the D2 lamp for the UV region (190 -- 370 nm) and the
W lamp for the visible region (371 －900 nm). Model 20A uses only the D2 lamp
(190－700 nm).
When the angle of mirror M1 is in the position shown, the light from the D2 lamp
is reflected and focused through the quartz window and enters the slit. When the
angle position of mirror M1 is switched, the light from the W lamp passes
through a stray light cut-filter (short wavelengths) and heat-absorbing filter, then
in the same manner is reflected and focused by mirror M1 and passes through the
quartz window and enters the slit. A filter assembly (high order cut-filter or
blocking filter) is inserted in front of the slit, based on the wavelength setting.
The blocking filter is inserted to detect zero order light. The high order cut-filter
is inserted in front of the slit to filter higher order spectra in the specified
wavelength region corresponding to the wavelength setting. The filter is inserted
in front of the slit at the 371－700 nm range for model 20A and 701 nm -- 900 nm
for model 20AV. After the light beam passes through the slit, it is reflected and
focused by mirror M2 and hits a holographic grating of 1600 grooves per
millimeter, where it is separated into its spectrum. The light separated by the
grating emerges as parallel light beams that are reflected by mirror M3 and are
wide enough to straddle and enter both of the sample and reference cells. The
spectrum is generated in an orientation perpendicular to the line bisecting both
cells, so both cells receive identical light wavelengths. After passing through each
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