Logarithmic primary testing system for security validation

摘要

Apparatus for performing tests for determining the validity of a paper purported to be a valid instrument is presented. Fundamentally, the invention comprises a tray for receiving a paper offered as a valid instrument and maintaining the same in sliding relationship between a light source and reticle. A photocell is operatively connected to the reticle and senses light passing from the light source and through the paper and reticle. The output of the photocell is applied to an operational amplifier having a dynamic feedback network and the output of this amplifier is characteristic of both a grid pattern upon the paper and the optical density thereof. This output is then passed to an amplifier circuit which establishes an optical density domain and is operative to pass a signal only if the paper falls within such domain. This output is then passed to appropriate integrating and comparator circuitry to ultimately determine the validity of the paper.