Importance

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Abstract

A self-calibrating obscuration smoke detector is provided along with a method for the operation thereof. A light source and a photodetector are mounted in spaced relation to one another with the output of the photodetector being a function of the amount of light sensed by the detector from the light source. The photodetector analog output is converted into digital signals by an A/D converter and digital signals are then delivered to a digital processor adapted to periodically calibrate the detector and to perform sampling operations between calibrations. Other sensing devices may be connected to the system with automatic self-calibrating capabilities with respect thereto including a temperature responsive element the output of which may be used to compensate for changes in ambient temperature. By using a pair of photodetecting cells directly visible to separate light sources or indirectly visible to a single source, a thermally stable system is provided where one cell provides a reference output for the other cell.

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First Claim