Light transmission type smoke detector

Abstract

A light transmission type smoke detector detecting smoke by sensing attenuation of light beam due to smoke is provided with a first voltage-holding circuit with a smaller time constant and a second voltage-holding circuit with a greater time constant both connected to a photoelectric transducer means; and an output from the photoelectric transducer means, which has sensed the light beam, charges the two voltage-holding circuits. When the photoelectric transducer means detects attenuation of the light beam by smoke, the first voltage-holding circuit holds the output voltage of the photoelectric transducer means for a relatively short time while the second voltage-holding circuit holds the output voltage for a relatively long time. The detector is further provided with a comparing circuit, which compares the output voltage of the first voltage-holding circuit and that of the second voltage-holding circuit and gives an alarm when the output of the first voltage-holding circuit falls lower than that of the second voltage-holding circuit. By means of the above-mentioned mechanism, the detector can compensate the effect of the slow attentuation of light beam caused by some factors other than smoke such as deterioration of the light source or light-receiving element and/or contamination of the optical system, and thus is prevented from mis-alarming.

Dependencies are inferred from the claim text.