Description of the AF45 sensor
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optek-Manual--1004-2003-02--AF45-US-2011-01-04
www.optek.com
Attenuation of light intensity, as a result of absorption and / or scattering of
substances in the process medium, is described by the Lambert-Beer Law. It
states, the logarithm of the transmission loss is proportional to concentration of
the substance. This is true for dissolved substances and undissolved material.
Depending on the particular material properties, concentrations can be detected
in ppm as well as in %.
According to this law, the extinction coefficient, defined through ingredient and
wavelength, affects the logarithm of the transmission loss, too. Therefore, the
choice of wavelength or range of wavelengths is of decisive importance for the
measurement and is defined for each measurement type with the help of optical
filters.
The third factor of influence in the Lambert-Beer Law is the path length of light
passing through the process medium. Equally proportional, the path length, too,
is an important aspect with regard to specification of a photometer. The distance
to be covered by light is defined through the optical path length (OPL), that is the
distance between the windows of a sensor body. In the technical data, OPL is
always given corresponding to window combination A-A.
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