Patent ID: 6396405
Filing Date: 2002-05-28
Classification: G08B

Abstract:
A self-contained smoke alarm that automatically tests its own calibration, comprising:(a) a signal sampler, within the smoke alarm itself, cooperating with a radiation sensor to produce acquired signal samples indicative of periodic measurements of a smoke level in a spatial region, the production of each of the acquired signal samples being initiated within the smoke alarm itself; (b) an alarm circuit, within the smoke alarm itself, comprising: an excessive-smoke level corresponding to an ambient smoke level that indicates an excessive smoke concentration; a signal tester having an output and being responsive to a number of the acquired signal samples comprising all or fewer than all of the acquired signal samples to determine whether the number of acquired signal samples corresponds to a smoke level that exceeds the excessive-smoke level, each such determination being initiated within the alarm itself; a humanly perceptible alarm indicator with at least two states; and circuitry, responsive to the output of the signal tester, that changes the state of the alarm indicator when a determined number of acquired signal samples exceed the excessive-smoke level within a time period; and (c) a calibration-testing circuit, within the smoke alarm itself, comprising: upper and lower limits representing smoke levels respectively greater than and less than an ambient smoke level to provide a specified sensitivity range of alarm-circuit operation; a calibration tester, with an output, comparing at least some of the acquired signal samples to the upper and lower limits, each comparison being initiated within the smoke alarm itself; a humanly perceptible calibration indicator, having at least two states; and circuitry, operatively associated with the output of the calibration tester, that changes the state of the calibration indicator in response to the output of the calibration tester, whereby the smoke alarm gives a humanly perceptible indication of a smoke-alarm condition when a smoke-alarm condition exists, and gives a humanly perceptible indication of an out-of-calibration condition when the alarm circuit is out of calibration.