Photoelectric smoke detecting apparatus

Abstract

A photoelectric smoke detecting apparatus capable of generating analog data accurately indicating a smoke density regardless of a presence or absence of contamination. A control unit for outputting the analog data corresponding to the smoke density based on a detection value derived from the output of a smoke sensor includes a smoke density arithmetic module having a characteristic function for converting the detection value to a smoke density value, a zero-density detection value storage device for storing a detection value at a time point when the smoke density is zero as a zero-density detection value, a change ratio arithmetic module designed for arithmetically determining a ratio of change representing a change of the zero-density detection value, and a compensation arithmetic module designed for compensating conversion characteristic for converting the detection value to the smoke density value based on the ratio of change. The compensation arithmetic module is designed to cause the smoke density arithmetic module to generate the smoke density value in such a manner to counter a change of an output characteristic of the detection value for of the smoke density, which change depends on the ratio of change. A self- or auto-compensation function against aged deterioration of the detection value due to contamination is realized.