Alarm detection device and method
First Claim
1. An alarm detection device comprising:
- a microphone;
a filter that filters the output of the microphone;
a comparator that operates on the output of the filter;
a counter that is locked or gated by the output of the comparator; and
a controller that samples the output of the counter at periodic intervals.
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Abstract
An audible alarm detector is disclosed, consisting of a microphone, band-pass filter, counter and controller. The microphone converts the acoustic signal to an electrical signal for further processing. The band-pass filter removes frequencies different from the nominal frequency of a pulsed tone alarm. The counter detects the fundamental frequency of the filtered signal in sequential time intervals. The controller compares the counter'"'"'s output for each time interval with the nominal count for the expected alarm frequency. The controller also compares the results from sequential time intervals against the nominal time-sequence of the anticipated, pulsed-tone alarm. A sufficiently close match results in a positive detection condition. An audible alarm detection method is also disclosed, consisting of low-pass filtering, followed by baseline-comparison, followed by counting, followed by discrimination based on counts, followed by comparison of discriminator output sequence versus the nominal sequence.
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Citations
11 Claims
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1. An alarm detection device comprising:
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a microphone; a filter that filters the output of the microphone; a comparator that operates on the output of the filter; a counter that is locked or gated by the output of the comparator; and a controller that samples the output of the counter at periodic intervals. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method for detecting an acoustic alarm comprising:
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electromechanical conversion of the acoustic signal to electrical signal; time-domain filtering of the signal by analog means; comparison of the filtered signal to a reference level close to the quiescent level of the filtered signal; counting of the transitions of the comparison output; sampling of accumulated counts from the counting step at periodic intervals; subtraction of successive sampled counts from the sampling step; and comparison of the subtraction results with a nominal pattern. - View Dependent Claims (8, 9, 10, 11)
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Specification