Fire sensor cross-correlator circuit and method
First Claim
1. A cross-correlation circuit for fire sensing comprising:
- first and second parallel signal channels for responding to long wavelength and short wavelength radiation, respectively;
said first channel including a short wavelength detector, an amplifier, a low pass filter, and signal sampling means coupled together in series;
said second signal channel including a long wavelength detector, an amplifier, a low pass filter and signal sampling means coupled together in series;
a signal multiplier stage coupled to receive the sampled signal outputs of the two signal channels and multiply sampled signals together by pairs; and
means coupled to the output of said multiplier stage for summing the sampled pair products in order to develop a cross-correlation function signal corresponding to said signals from said signal channels which is indicative of the detection by both of said detectors of radiation from a fire source.
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Abstract
A cross-correlation fire sensor circuit includes detectors responsive to heat and light radiation, respectively. Electrical signals from the detectors are processed in two distinct channels through low pass filters and samplers. The sampled signals from the two channels are multipled together and the products are summed over a selected interval to provide a correlation function. This function is compared with an adjustable threshold to provide an indication of fire sensing. The circuit is also included as an adjunct to an existing system to provide improved sensitivity for fire sensing in the presence of noise and enhanced discrimination against false alarms. A ratio window detector circuit is disclosed as an alternative cross-correlator for detected radiation.
28 Citations
36 Claims
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1. A cross-correlation circuit for fire sensing comprising:
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first and second parallel signal channels for responding to long wavelength and short wavelength radiation, respectively; said first channel including a short wavelength detector, an amplifier, a low pass filter, and signal sampling means coupled together in series; said second signal channel including a long wavelength detector, an amplifier, a low pass filter and signal sampling means coupled together in series; a signal multiplier stage coupled to receive the sampled signal outputs of the two signal channels and multiply sampled signals together by pairs; and means coupled to the output of said multiplier stage for summing the sampled pair products in order to develop a cross-correlation function signal corresponding to said signals from said signal channels which is indicative of the detection by both of said detectors of radiation from a fire source. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A cross-correlator fire sensor circuit comprising:
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a first detector adapted to generate an electrical signal in response to radiation of a first selected wavelength in a range above approximately 4.0 microns; a second detector adapted to generate an electrical signal in response to radiation of a second selected wavelength in a range below approximately 4.0 microns; first and second signal channels coupled respectively to the first and second detectors, each of said channels including a low pass filter in series with means for sampling the signals passed by the low pass filter; and means for cross-correlating sampled signals, by pairs, to develop a fire sense signal when the correlation between signal pairs exceeds a predetermined threshold level. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
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30. The method of sensing a fire from incident radiation in wavelength ranges respectively above and below 4.0 microns comprising the steps of:
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detecting short wavelength radiation in the range of 0.8 to 1.1 microns; detecting long wavelength radiation in the range of 7 to 25 microns; processing signals from detected radiation in separate signal channels, one for each wavelength range, wherein each signal channel includes a low pass filter; sampling the signals at the outputs of the respective low pass filters in the separate channels; and further processing said signals by sample pairs and generating a fire sense signal upon the occurrence of a correlation between corresponding pairs of signals. - View Dependent Claims (31, 32, 33, 34, 35, 36)
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Specification