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Abstract

A motion detector responsive to infrared radiation, e.g. for use in burglar-alarm installations, comprises a pair of juxtaposed sensors monitoring adjacent fields of view of a space to be surveyed, giving rise to output signals of opposite polarity upon detecting a disturbance in their respective fields. These output signals are fed to an evaluator comprising two complementary transistors with interconnected emitters and interconnected bases whose junctions are separated by a resistive branch of an RC network, the emitter junction receiving the output signals while the base junction is capacitively coupled to ground or some other point of fixed potential. The collectors of these transistors, energized via respective resistors from opposite terminals of a d-c supply, are connected to respective timers working into a common AND gate which triggers an alarm when an alternation of output signals from the two sensors renders the timers conductive for overlapping periods.

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First Claim