Patent ID: 8510068

Claim:
A photoelectric smoke sensor comprising: detection means including a light-emitting element and a light-receiving element housed within a smoke detection space, for outputting a detection value of the light-receiving element for receiving light scattered by smoke, the light being emitted from the light-emitting element; a smoke-density computing section for converting the detection value output from the detection means into smoke-density data based on a conversion formula; a zero detection value storing section for storing a zero detection value corresponding to the detection value of the light-receiving element when a smoke density is zero; an initial zero detection value storing section for storing an initial zero detection value corresponding to an initial value of the zero detection value; a moving average value calculating section for calculating a moving average value of the detection values output from the detection means; a zero detection value updating section for dividing the initial zero detection value by a predetermined correction factor to calculate a new zero detection value when a sensitivity of the detection means is decreased as compared with that in an initial state, and in addition, when a rate of change in the moving average value with respect to the zero detection value exceeds a predetermined value; and a detection value correcting section for multiplying a difference between the detection value and the zero detection value updated by the zero detection value updating section by the predetermined correction factor to correct the detection value, wherein the smoke-density computing section converts the detection value corrected by the detection value correcting section into the smoke-density data based on the conversion formula.