(57) A fire sensor discriminates between fires and the flash caused by a projectile piercing
the wall of a protected area. The sensor system comprises first and second radiant
energy detectors, each sensitive to radiation within different spectral bands. Each
detector is coupled to a control signal means for generating a control signal when
the radiation sensed exceeds a predetermined amplitude. A third control signal means
is responsive to the first and second detectors, and is operative to generate a third
control signal whenever the ratio of the amplitude of the energy sensed by the first
detector to the amplitude of the energy sensed by the second detector is less than
a predetermined value; not generate the third control signal whenever the ratio of
amplitudes exceeds the predetermined value; and delay generation of the third control
signal for a predetermined period of time after the ratio of amplitudes falls below
the predetermined value. An output control signal is then generated only if all three
control signals are simultaneously generated. The decay of the flash radiation is
thereby electrically simulated, allowing the fire sensor to sense whether a fire develops
after the flash passes.
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