PR-680/680L User Manual
1
T
HEORY OF
O
PERATION
S
PECTRORADIOMETER
The PR-680/680L combines the functionality of a Spectroradiometer and filter photometer. As a
Spectroradiometer, it collects the optical radiation (light) through the objective lens or other optical accessory.
The signal then passes through the aperture (hole) in the aperture mirror to the diffraction grating (see Figure
47). The grating breaks up the light into its component wavelengths much like a prism turns white light into a
rainbow. A broad band light such as sunlight is composed of a large number of different wavelengths of light.
When the diffraction grating is exposed to this type of light, it will refract the light at several angles thus creating
a dispersed spectrum much like a rainbow. Similarly, if the grating is exposed to a source such as a laser which
emits a nearly monochromatic wavelength of light, only the wavelength(s) of the laser will be refracted.
FIGURE 45
–
SPECTRUM MEASURED BY THE PR-680/680L
The measurement wavelength range is 380 nanometers (nm) (violet) to 780 nm (deep red)
–
the visible
spectrum of the electromagnetic spectrum (see Figure 45).
The diffracted spectrum is then dispersed onto the detector. For the PR-680/680L, the detector is comprised of
128 individual elements. The PR-680/680L detector utilizes 256 elements. Each of the detector elements in
both instruments samples a unique color.
During a measurement, the optical radiation (light) is sampled for a period of time determined by the Adaptive
Sensitivity
™
algorithm. Adaptive Sensitivity automatically determines the correct integration (exposure) time
based on the available signal. Following the light measurement, a measurement of the dark current of the
detector is made for the same length of time that was used for the light measurement. The dark measurement
is then subtracted from the light measurement yielding the contribution of light for each detector element.
FIGURE 46 - PR-680/680L SIMPLIFIED BLOCK DIAGRAM
380 nm
500 nm
600 nm
780 nm
Spectrometer
CPU