Secondary detection circuit with sharp cutoff for security validating

Claim 2

In a paper security validating apparatus having means for scanning a portion of the security to determine the authenticity thereof and to produce an output signal when the scanning indicates a valid security, the improvement comprising: means for illuminating a portion of the security; a first sensor for detecting the amount of illumination reflected from the illuminated portion of the security; a reference surface, illuminated by the means for illuminating and having substantially the same reflective qualities as the portion of the security being illuminated; a second sensor for detecting the amount of illumination reflected from the reference surface; means for comparing the output signals of the first and second sensors; and means responsive to the comparing means for blocking the output signal of the authenticity determining means when the output signals of the first and second sensors differ by more than a predetermined amount.

Claim 3

The improvement according to claim 1 wherein the first and second sensors are silicon solar cells.

Claim 4

The improvement according to claim 2 when the first and second sensors have closely matched characteristics and are connected in a series-aiding network.

Claim 5

The improvement accordiNg to claim 1 wherein the means for illuminating and the sensors are located on the opposite side of the paper security from the means for scanning.

Claim 6

The improvement according to claim 1 wherein the means for illuminating is an infrared light source.

Claim 7

Apparatus for determining the authenticity of a paper security, comprising: a first detection circuit including means to scan a portion of the security and means to produce an output signal when the scanning means detects an apparently authentic security; and a second detection circuit for scanning a second portion of the security and operative to block the output signal of the first detection circuit when an invalid security is detected, the second detection circuit including means for illuminating the second portion of the security, a sensor for detecting the amount of illumination reflected from the second portion of the security, circuit means receiving the output of the sensor and operative to block the first detector circuit output signal when the output of the sensor departs from a reference level by more than a predetermined amount, wherein the first detector circuit means to produce an output signal includes a first normally non-conductive transistor which becomes conductive when an apparently valid security is scanned, the circuit means of the second detection circuit including a second transistor which is normally non-conductive but becomes conductive upon detection of an invalid security by the second detection circuit, conduction of the second transistor holding the first transistor in a non-conductive state, wherein the circuit means of the second detector circuit includes a second sensor illuminated by reflection from the means for illuminating, the first and second sensors being connected in a series-aiding network, and where a reflective surface is provided to direct illumination from the means to illuminate uniformly to the second sensor.

Claim 8

Apparatus for determining the authenticity of a paper security, comprising: a first detection circuit including means to scan a portion of the security and means to produce an output signal when the scanning means detects an apparently authentic security; and a second detection circuit for scanning a second portion of the security and operative to block the output signal of the first detection circuit when an invalid security is detected, the second detection circuit including means for illuminating the second portion of the security, a sensor for detecting the amount of illumination reflected from the second portion of the security, circuit means receiving the output of the sensor and operative to block the first detector circuit output signal when the output of the sensor departs from a reference level by more than a predetermined amount, wherein the first detector circuit means to produce an output signal includes a first normally non-conductive transistor which becomes conductive when an apparently valid security is scanned, the circuit means of the second detection circuit including a second transistor which is normally non-conductive but becomes conductive upon detection of an invalid security by the second detection circuit, conduction of the second transistor holding the first transistor in a non-conductive state, wherein the circuit means of the second detector circuit includes a second sensor illuminated by reflection from the means for illuminating, the first and second sensors being connected in a series-aiding network, and where a reflective surface is provided to direct illumination from the means to illuminate uniformly to the second sensor.

Claim 9

Apparatus according to claim 6 wherein the sensors are silicon solar sensors having closely matched characteristics.

Claim 10

Apparatus according to claim 7 wherein the reflective surface is adjustably mounted to controllably vary the amount of reflected illumination to the second sensor.

Claim 11

Apparatus according to claim 6 further including an amplifier receiving the output of the sensor network and controlling the second transistor.

Claim 12

Apparatus according to claim 9 further including a zener diode in series connection between the amplifier and the second transistor to block current flow from the amplifier until the amplifier signal exceeds a predetermined level.

Claim 13

Apparatus according to claim 10 further including a third transistor which is normally non-conductive and which biases the second transistor to a conductive state when the third transistor conducts, a second zener diode being provided between the amplifier and the third transistor to permit current flow to the third transistor only when the amplifier output is below a second predetermined level.