Smoke detecting apparatus for fire alarm

• US 5,598,147 A
• Filed: 11/02/1995
• Issued: 01/28/1997
• Est. Priority Date: 11/04/1992
• Status: Expired due to Fees

• Current Assignee: Nohmi Bosai Limited (Secom Company Limited)
• Original Assignee: Nohmi Bosai Limited (Secom Company Limited)
• Inventors: Kobayashi, Ryousaku, Ito, Hideo, Mochizuki, Mikio
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): MANNAVA, ASHOK K
• Application Number:
  US08/552,175
• Time in Patent Office: 453 Days
• Field of Search: 340/628, 340/629, 340/630, 250/573, 250/574, 250/575, 250/576, 356/437, 356/438, 356/439
• US Class Current: 340/630
• CPC Class Codes: G08B 17/107 for detecting light-scattering due to smoke
• CPC Class Codes: G08B 29/043 of fire detection circuits

Abstract

A smoke detecting apparatus for a fire alarm has a smoke chamber into which smoke to be detected is introduced, a light emitting lamp disposed in the smoke chamber, a light receiving element disposed in the smoke chamber so as to receive the light emitted from the light emitting lamp, an amplification device for amplifying an output signal from the light receiving element, a detection device for detecting the density of the smoke on the basis of an output signal from the amplification device, a comparison device for comparing the value of the output signal from the amplification device with a fixed value, an abnormality output device for outputting an abnormality indication when the value of the output signal from the amplification device is judged to be smaller than the fixed value by the comparison device, an augmentation command switch for commanding augmentation of the value of the output signal from the amplification device, and an augmentation device for augmenting, in accordance with a command from the augmentation command switch, the value of the output signal of the amplification device which is input to the comparison device.

Claims

1. A smoke detecting apparatus comprising:

a smoke chamber into which smoke to be detected is introduced;

a light emitting lamp disposed in said smoke chamber;

a light receiving element disposed in said smoke chamber so as to receive light emitted from said light emitting lamp and scattered by said smoke;

amplification means for amplifying an output signal from said light receiving element;

augmentation means for augmenting, upon receipt of a command, the output signal of said amplification means; and

control means for (a) detecting a density of the smoke on the basis of an output signal from said amplification means, (b) comparing an amplitude of the output signal from said amplification means with a fixed value, and (c) generating an abnormality indication when the amplitude of the output signal from said amplification means is judged to be smaller than said fixed value;

augmentation command switch means manually switched on to apply said command to said augmentation means, the amplitude of the output signal from said amplification means being gradually augmented every time said augmentation command switch means is manually switched on when the abnormality indication is generated by said control means.

2. An apparatus according to claim 1 wherein said amplification means includes a first amplifier for amplifying the output signal from said light receiving element.

3. An apparatus according to claim 2 wherein said augmentation means includes a first gain switching circuit for augmenting the gain of said first amplifier.

4. An apparatus according to claim 2 wherein said augmentation means includes a second amplifier for amplifying an output signal from said first amplifier.

5. An apparatus according to claim 1 wherein said amplification means includes:

a first amplifier for amplifying the output signal from said light receiving element;

an A/D conversion circuit for A/D-converting an output signal from said first amplifier; and

a multiplication circuit for augmenting an output of said A/D conversion circuit.

6. An apparatus according to claim 5 wherein said augmentation means includes a multiplying factor augmenting circuit for augmenting a multiplying factor set in said multiplication circuit.

7. An apparatus according to claim 1 wherein said amplification means includes:

a first amplifier for amplifying the output signal from said light receiving element;

an A/D conversion circuit for A/D-converting an output signal from said first amplifier; and

an addition circuit for adding an additions, value to an output of said A/D conversion circuit.

8. An apparatus according to claim 7 wherein said augmentation means includes an addition value augmenting circuit for augmenting an addition value set in said addition circuit.

9. A smoke detecting apparatus comprising:

a smoke chamber into which smoke to be detected is introduced;

a light emitting lamp disposed in said smoke chamber;

a light receiving element disposed in said smoke chamber so as to receive light emitted from said light emitting lamp and scattered by said smoke;

amplification means for amplifying an output signal from said light receiving element;

detection means for detecting a density of the smoke on the basis of an output signal from said amplification means;

comparison means for comparing an amplitude of the output signal from said amplification means with a fixed value;

augmentation command switch means manually switched on to generate a command when the amplitude of the output signal from said amplification means is judged to be smaller than said fixed value by said comparison means; and

an augmentation means for augmenting the output signal of said amplification means in accordance with the generation of said command by said augmentation command switch means, the amplitude of the output signal from said amplification means being gradually augmented every time said augmentation command switch means is manually switched on when the amplitude of the output signal from said amplification means is judged to be smaller than said fixed value by said comparison means.

10. An apparatus according to claim 9 further comprising an abnormality output means for outputting an abnormality indication when the value of the output signal from said amplification means is judged to be smaller than said fixed value by said comparison means.

11. An apparatus according to claim 9 wherein said amplification means includes a first amplifier for amplifying the output signal from said light receiving element.

12. An apparatus according to claim 11 wherein said augmentation means includes a first gain switching circuit for augmenting the gain of said first amplifier.

13. An apparatus according to claim 11 wherein said augmentation means includes a second amplifier for amplifying an output signal from said first amplifier.

14. An apparatus according to claim 9 wherein said amplification means includes:

a first amplifier for amplifying the output signal from said light receiving element;

an A/D conversion circuit for A/D-converting an output signal from said first amplifier; and

a multiplication circuit for augmenting an output of said A/D conversion circuit.

15. An apparatus according to claim 14 wherein said augmentation means includes a multiplying factor augmenting circuit for augmenting a multiplying factor set in said multiplication circuit.

16. An apparatus according to claim 9 wherein said amplification means includes:

a first amplifier for amplifying the output signal from said light receiving element;

an A/D conversion circuit for A/D-converting an output signal from said first amplifier; and

an addition circuit for adding an addition value to an output of said A/D conversion circuit.

17. An apparatus according to claim 16 wherein said augmentation means includes an addition value augmenting circuit for augmenting an addition value set in said addition circuit.