2 • Description
Doc. 031644-02 9/03
2-5
Optical System
Component
Function
Tungsten Lamp
The light source for visible and near-infrared wavelengths
(380 nm to 800 nm). The tungsten lamp is focused through an
opening in the internal structure of the deuterium lamp; this
allows the lamps to share the optical axis to the source lens.
Visible Focus Lens
Focuses the visible light from the tungsten lamp to the through-
hole of the deuterium lamp.
Deuterium Lamp
The light source for UV wavelengths (190 nm to 380 nm); also
used to check the wavelength calibration.
Source Lens
Receives the light from the tungsten and deuterium lamps and
focuses it so that the beam passes through the flow cell.
Flow Cell
The measurement site for sample absorbance. The cell has a flat
window on each side.
Spectrograph Lens
Receives the light from the flow cell and focuses it onto the slit.
Filter Paddle
The motorized filter paddle in the spectrograph has three
positions:
•
Open
= Light passes, unobstructed, along the light path when
the holmium oxide filter is moved out of the light path.
•
Blocked
= No light passes along the light path; used to
measure the dark signal without turning off the lamps.
•
Holmium
= Places the holmium oxide filter in the light path;
used to verify wavelength accuracy.
Slit
The width of the slit (equivalent to 1 nm) optimizes the optical
resolution.
Grating
Diffracts the light beam into its component wavelengths and
directs the light onto the photodiode array.
Photodiode Array
A series of 1024 photosensitive elements. Each element measures
a narrow band of the spectrum. A spectrum is obtained by
measuring the light intensity of each wavelength and reporting the
range of results.
