Smoke sensor and electronic equipment

• US 7,659,986 B2
• Filed: 11/14/2008
• Issued: 02/09/2010
• Est. Priority Date: 11/15/2007
• Status: Active Grant

• Current Assignee: Fenwal Controls Of Japan, Ltd., Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Fenwal Controls Of Japan, Ltd., Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Sugimoto, Kohichiroh
• Primary Examiner(s): Pham; Hoa Q
• Application Number:
  US12/271,700
• Publication Number:
  US 20090128821A1
• Time in Patent Office: 452 Days
• Field of Search: 356/437, 356/438, 250573-574, 340/628, 340/630
• US Class Current: 356/438
• CPC Class Codes: G01N 2021/4707 Forward scatter; Low angle scatter
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/53 within a flowing fluid, e.g. smoke

Abstract

In a smoke sensor, a first light-receiving element which receives light from a light-emitting element and is disposed in a position where the quantity of received light changes according to a density of smoke and a second light-receiving element which monitors the quantity of light of the light-emitting element are arranged symmetrically with respect to the light-emitting element. Furthermore, a signal from the first light-receiving element and a signal from the second light-receiving element are amplified by an identical amplifier circuit. In a microcomputer, the density of smoke is computed based on a difference between an output obtained by amplifying an output of the first light-receiving element with the amplifier circuit and an output obtained by amplifying an output of the second light-receiving element with the amplifier circuit.

Claims

1. A smoke sensor comprising:

a light-emitting device emitting light;

a first chamber;

a smoke passage providing communication between inside of the first chamber and outside of the first chamber;

a second chamber having a density of smoke of a predetermined value;

a first light-receiving element receiving light which has traveled in the first chamber after being emitted from the light-emitting device directly to the first chamber or light which has traveled in the first chamber after being emitted from the light-emitting device and entering the first chamber through only a place having a density of smoke of zero;

a second light-receiving element receiving light which has traveled in the second chamber after being emitted from the light-emitting device directly to the second chamber or light which has traveled in the second chamber after being emitted from the light-emitting device and entering the second chamber through only a place having a density of smoke of zero;

a first switch receiving and selectively outputting a signal from the first light-receiving element and a signal from the second light-receiving element;

an amplifier section amplifying a signal from the first switch; and

a density detecting section detecting a density of smoke in the first chamber on the basis of a first amplified signal which is a signal from the first light-receiving element amplified by the amplifier section and a second amplified signal which is a signal from the second light-receiving element amplified by the amplifier section.

2. The smoke sensor as claimed in claim 1, wherein:

each of the first amplified signal and the second amplified signal is a voltage signal;

a light-receiving surface of the first light-receiving element is disposed in the first chamber and a light-receiving surface of the second light-receiving element is disposed in the second chamber;

a distance from a light-emitting surface of the light-emitting device to the light-receiving surface of the first light-receiving element is same as a distance from the light-emitting surface to the light-receiving surface of the second light-receiving element;

the predetermined value of the density of smoke in the second chamber is zero; and

the first amplified signal has a magnitude same as a magnitude of the second amplified signal in a state that the density of smoke in the first chamber is zero.

3. The smoke sensor as claimed in claim 1, wherein the amplifier section has one or more amplifiers.

4. The smoke sensor as claimed in claim 1, wherein:

the amplifier section has a current-voltage conversion section;

the current-voltage conversion section has an input terminal connected with an output terminal of the first switch, an output terminal, and a resistor device connected between the input terminal and the output terminal of the current-voltage conversion section; and

the resistor device provides resistances which are different between a case that a signal from the first light-receiving element is processed by the current-voltage conversion section and a case that a signal from the second light-receiving element is processed by the current-voltage conversion section.

5. The smoke sensor as claimed in claim 4, wherein:

the resistor device includes a first resistor one end of which is connected with the input terminal of the current-voltage conversion section, and a second resistor one end of which is connected with the input terminal of the current-voltage conversion section;

the current-voltage conversion section further has a second switch an output terminal of which is connected with the output terminal of the current-voltage conversion section; and

the smoke sensor further comprises a control circuit which outputs a control signal for connecting an input terminal of the second switch to another end of the first resistor when a signal from the first light-receiving element is processed by the current-voltage conversion section, while outputting a control signal for connecting the input terminal of the second switch to another end of the second resistor when a signal from the second light-receiving element is processed by the current-voltage conversion section.

6. The smoke sensor as claimed in claim 4, wherein the resistor device has a positive temperature coefficient.

7. The smoke sensor as claimed in claim 1, further comprising a flat plate-shaped wall, wherein:

the first light-receiving element, the second light-receiving element, the first switch, and the amplifier section are included in one integrated circuit;

a distance from a light-emitting surface of the light-emitting device to a light-receiving surface of the first light-receiving element is same as a distance from the light-emitting surface to a light-receiving surface of the second light-receiving element;

the first chamber exists on one side of the flat plate-shaped wall, while the second chamber exists on an opposite side of the flat plate-shaped wall; and

the smoke sensor further comprises a first interceptor preventing light from the light-emitting device from directly entering the light-receiving surface of the first light-receiving element and a second interceptor preventing light from the light-emitting device from directly entering the light-receiving surface of the second light-receiving element.

8. Electronic equipment comprising the smoke sensor as claimed in claim 1.