Alarm system control circuit
First Claim
1. A smoke detection alarm system comprising:
- smoke detection means responsive to a clock signal applied thereto for producing an alarm signal representative of the presence of smoke;
means for providing an output indication of the presence of smoke upon the production of a predetermined number of consecutive alarm signals by the smoke detection means;
phase selection means for producing a phase selection signal and for changing the phase selection signal in response to the production of an alarm signal by the smoke detection means;
clock means responsive to the phase selection signal and to an A.C. line signal for producing a variable phase clock signal having a phase relationship with respect to the A.C. line signal which is determined by the phase selection signal; and
means for applying the variable phase clock signal to the smoke detection means.
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Accused Products
Abstract
A circuit for reducing or eliminating the sensitivity of alarm circuitry to false alarms caused by noise occurring synchronously with a 60 Hz line voltage. The 60 Hz line signal is applied to a variable-threshold circuit which produces a 60 Hz clock signal. The clock signal produced by the variable-threshold circuit may be selected to occur at different points during a cycle of the 60 Hz line signal. In response to successive alarm signals, the clock signal produced by the variable-threshold circuit occurs with different phasing relationships to the 60 Hz line signal. Before an alarm indication is made, an alarm signal must be provided by the smoke sensor in response to a plurality of successive samples. If, the alarm signal is a false alarm signal produced by the pickup of noise pulses which are synchronous with the 60 Hz line signal, subsequent samples taken at different points during a cycle of the line frequency sample the output from the smoke detection circuitry during periods when the alarm circuitry does not pick up such synchronous noise pulses; and the false signal is rejected.
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Citations
24 Claims
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1. A smoke detection alarm system comprising:
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smoke detection means responsive to a clock signal applied thereto for producing an alarm signal representative of the presence of smoke; means for providing an output indication of the presence of smoke upon the production of a predetermined number of consecutive alarm signals by the smoke detection means; phase selection means for producing a phase selection signal and for changing the phase selection signal in response to the production of an alarm signal by the smoke detection means; clock means responsive to the phase selection signal and to an A.C. line signal for producing a variable phase clock signal having a phase relationship with respect to the A.C. line signal which is determined by the phase selection signal; and means for applying the variable phase clock signal to the smoke detection means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. In an alarm system of the type having:
- means for producing a periodically-occurring sampling signal in response to an A.C. line signal;
means for testing for the presence of an alarm condition in response to the sampling signal and for producing an alarm signal upon the detection of the presence of an alarm condition; and
means for producing an output signal in response to a predetermined number of consecutive alarm signals produced by the testing means in response to consecutive sampling signals;
the improvement comprising;means for changing the phase relationship between the A.C. line signal and the sampling signal in response to an alarm signal.
- means for producing a periodically-occurring sampling signal in response to an A.C. line signal;
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12. In an alarm system for the type having:
- means for producing a periodically-occurring sampling signal in response to an A.C. line signal;
means for testing for the presence of an alarm condition in response to the sampling signal and for producing an alarm signal upon the detection of the presence of an alarm condition; and
means for producing an output signal in response to a predetermined number of consecutive alarm signals produced by the testing means in response to consecutive sampling signals;
the improvement comprising;means for changing the phase relationship between the A.C. line signal and the sampling signal in response to an alarm signal, including; means for producing a clock signal having one of a plurality of phasing relationships with respect to the A.C. line signal; and means for selecting one of the plurality of phasing relationships and for changing the selected phasing relationship in response to an alarm signal produced by the testing means. - View Dependent Claims (13, 14, 15, 16)
- means for producing a periodically-occurring sampling signal in response to an A.C. line signal;
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17. For use in an alarm system, a circuit for producing a clock signal derived from an A.C. line signal, comprising:
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means for producing a variable-phase clock signal in response to the A.C. line signal, the variable-phase clock signal having a selected one of a plurality of possible phase relationships to the A.C. line signal, the selected one being determined in response to a phase selection signal; means for producing the phase selection signal and for changing the phase selection signal in response to an alarm signal from the alarm system, including; phase-selection means for producing phase selection signals to sequentially cycle through each of the plurality of phase relationships in response to the occurrence of successive alarm signals; and means for maintaining the presently selected phase relationship in the absence of an alarm signal. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24)
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Specification