Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1997-03-07
1998-08-18
Swarthout, Brent A.
Communications: electrical
Condition responsive indicating system
Specific condition
340550, 340544, G08B 1300
Patent
active
057963363
ABSTRACT:
To improve accuracy in detection of glass breakage, a microphone converts a glass breaking sound into an electrical signal, and high-pass filters and extract high frequency components of 2 kHz or higher and 150 Hz or higher, respectively, from the signal. A half-wave rectifier circuit half-wave rectifies these signals and an amplifier amplifies them. The output of the amplifier is smoothed by smoothing circuits. When the output of the smoothing circuit reaches a predetermined value, a trigger circuit outputs a start pulse to a start terminal of a CPU. Started by the start pulse, the CPU inputs the outputs of the smoothing circuits, converts them into digital values using an A/D converter, determines integrals over 30 ms, and stores the integrals into a RAM. Then, the CPU calculates a ratio of the integral of the output of the smoothing circuit to the integral of the output of the smoothing circuit based on a program stored in a ROM. If the ratio is within a predetermined range, the CPU determines that the detected acoustic waves are the first waves of a glass breaking sound and outputs a glass breakage detection signal.
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Ishino Hirotugu
Kurahashi Akira
Denso Corporation
Swarthout Brent A.
Trieu Van T.
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