Circuit for sorting currency

A circuit arrangement for providing a digital representation of the intensity of light transmissivity of an article being transported through an examination station over an interval of time, said representation being compared to a predetermined light intensity reference level, said circuit arrangement determining fitness and wear characteristics of said article, and comprising:

• a first circuit means including a photosensitive element which is positioned at the examination station for receiving light transmitted through the article as said article is transported through the examination station, said first circuit means generating a first electrical signal having an amplitude which is proportional to the intensity of the light transmitted through said article;
• a second circuit means coupled to said first circuit means for forming the integral of said first electrical signal, said second circuit means including gating means, said gating means receiving a gating signal from a bill present comparator for enabling and disabling, representively, the second circuit means, said gating signal being representative of the presence and absence, respectively, of an article at the examination station;
• a bill present comparator operatively coupled to said gating means for generating and applying said gating signal to said gating means;
• comparator circuit means having first and second input terminals, said comparator circuit means providing a first DC output level when an input signal applied to said first terminal is greater in amplitude than a reference signal applied to said second input terminal, and, for providing a second DC output level when the amplitude of a signal applied to said first imput terminal is less than the amplitude of a refernce signal applied to said second input terminal;
• means for applying the integral of said first electrical signal to the first input terminal of said comparator circuit means;
• means for establishing and applying to the second input terminal of said comparator circuit means a reference signal having an amplitude representative of a predetermined light intensity;
• and
• compensating circuit means disposed at said examination station and operatively connected to said comparator circuit means for detecting variations in the light intensity at the examination station in the absence of an article at said examination station, and for varying the reference potential applied to said second input terminal of said comparator circuit means in response to said variations in light intensity.