Jadak PHOTO RESEARCH SpectraScan PR-655, Руководство пользователя

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PR-655/670 User Manual
53
T
HEORY OF
O
PERATION
The PR-655 and PR-670 are true Spectroradiometer. They collect 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 48). 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 46 – SPECTRUM MEASURED BY THE PR-655 AND PR-670
For the PR-655 and PR-670, the measurement wavelength range is 380 nanometers (nm) (violet) to 780 nm
(deep red)
– the visible spectrum of the electromagnetic spectrum (see Figure 46).
The diffracted spectrum is then dispersed onto the detector. For the PR-655, the detector is comprised of 128
individual elements. The PR-670 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 47 - PR-655 / PR-670 SIMPLIFIED BLOCK DIAGRAM
380 nm 500 nm 600 nm 780 nm
Spectrometer CPU