Importance

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Abstract

Motion is detected from a surveillance monitor by means of a photosensor attached to the monitor screen and an electric circuit connected to the sensor which generates an alarm signal in response to changes in the level of an electric output signal generated by the sensor. The sensor is housed within a suction cup which is readily attached to any part of the screen and is readily movable to any desired area of the screen to be monitored for motion. The electric circuit includes comparators which detect changes in light intensity greater than a predetermined magnitude defined by a window about a preselected voltage level. The circuit includes an operational amplifier and a transistor connected to the output of the sensor and the circuit provides an effective impedance equal to the impedance of the sensing device at various levels of intensity such that the reference voltage level, for detection purposes, is the same at all levels of steady state light intensity. The magnitude of the window is defined by a voltage divider having one end connected to the output of the operational amplifier and the window is adjusted with changes in average light intensity levels.

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First Claim