US 3,942,898 AGranted

Densitometer for measuring the density of an optical element such as a film badge

AssigneeBeckman Instruments, Inc.

InventorRobert J. Anderson

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Abstract

A densitometer for providing an output which is a function of the density of a film badge in a photodosimeter system. The light passing through the film badge is received by a photodiode which generates a current signal which is directly proportional to the intensity of the received light. The current signal is converted to a voltage signal, the converting means being biased so that the voltage signal is zero when no light is received by the photodiode. The voltage signal is applied, together with a reference voltage, to a log-ratio circuit which generates an output signal proportional to the log of the ratio of the reference voltage to the voltage signal, the output of the log-ratio circuit being displayed. A circuit is operative, when the film badge is removed from the light path, to adjust the reference voltage until the output of the log-ratio circuit is zero.

Claims9

Dependent claims

A densitometer for providing an output which is a function of the density of an optical element such as a film badge comprising:

a source of light;
means for holding said optical element in the path of said light, said optical element transmitting an amount of light which is inversely proportional to the density thereof;
detector means positioned to receive the light transmitted through said optical element for generating a first signal which is directly proportional to the intensity of the received light;
means for generating a reference signal;
circuit means responsive to said first signal and said reference signal for generating a second signal proportional to the log of the ratio of said reference signal to said first signal, said second signal being proportional to the density of said optical element;
means for displaying said second signal;
and
means operative when said optical element is removed from said light path for adjusting said reference signal until said second signal is zero.

5 more elements

Dependencies are inferred from the claim text.