Patent ID: 8552355

Claim:
A smoke sensor, comprising: a light-emitting section; a light-receiving section; a current-voltage conversion circuit; a current source; and a determination processing section, wherein the light-emitting section outputs pulsed light towards a sensing space at a predefined sensing period, the light-receiving section is disposed at a position not struck by direct light from the light-emitting section, but struck by light from the light-emitting section, that is diffused and reflected by smoke that flows into the sensing space, the current source causes a sensor current of a magnitude corresponding to a light reception intensity to flow in the light-receiving section, the current-voltage conversion circuit has a conversion section, the conversion section converts an input current to an output voltage and outputs the output voltage from an output terminal, and the input current is inputted into an input terminal of the conversion section connected to the light-receiving section, the determination processing section determines presence or absence of the smoke in the sensing space on a basis of the output voltage, the current-voltage conversion circuit has low-frequency correction means, and the low-frequency correction means extracts, of the output voltage, a low-frequency component that is not greater than or equal to a cut-off frequency that is lower than a frequency of a pulsed detection signal that is generated when the light-receiving section receives light from the light-emitting section, causes a flow of a correction current of a magnitude according to the low-frequency component, and uses a combined current of the correction current and the input current as the sensor current, to reduce thereby the input current by the correction current.