Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Patent
1991-03-13
1992-05-26
Howell, Janice A.
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
250214AG, 356443, 356444, G01N 2122
Patent
active
051171198
ABSTRACT:
A film densitometer for generating digital density values as a function of analog transmittance signals received at an input. A comparator coupled to the input compares the transmittance signals to one or more range references characterizing a plurality of ranges of transmittance signal magnitudes, and provides digital transmittance range signals as a function of the comparison. An amplifier amplifies the transmittance signals to provide amplified transmittance base signals. A gain control circuit coupled to the amplifier and the comparator controls the gain factor of the amplifier as a function of the magnitudes of the transmittance signals. The amplified transmittance base signals are converted to digital transmittance base values by an analog-to-digital converter. A lookup table of data characterizing the logarithmic relationship between transmittance base values and density base values is stored in base memory. A lookup table of data characterizing the relationship between the transmittance range signals and range gain values is stored in range memory. A digital processor accesses the memory as a function of the transmittance base values and transmittance range signals, and generates the digital density values as a function of a sum of the density base values and range gain values.
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Lemberger Richard R.
Schubert Paul C.
Griswold Gary L.
Howell Janice A.
Kirn Walter N.
Linder Walter C.
Minnesota Mining and Manufacturing Company
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