Electronic smoke detector

Abstract From the Canadian patent

In a combined obscuration and scattered-light smoke detector, light from a light source in a smoke chamber is reflected from an image-forming optical component onto a first light sensor which senses a reduced electrical signal in the presence of smoke while a second sensor, viewing light from the light source at an angle, senses an increased electrical signal in the presence of smoke. The output of each receptor is subjected to a band pass filter an, amplifier and a comparator; the resultant signals insure early and reliable activation of an alarm when even a low level of smoke is present in the smoke detector. A second light source having a wavelength different from that of the first light …