Light extinction smoke detector

• US 4,528,555 A
• Filed: 06/29/1983
• Issued: 07/09/1985
• Est. Priority Date: 12/11/1981
• Status: Expired due to Fees

• Current Assignee: Nohmi Bosai Kogyo Company Limited
• Original Assignee: Cerberus ABP Investor LLC (Cerberus Capital Management LP), Nohmi Bosai Kogyo Company Limited
• Inventors: Ishii, Kenji, Yasukawa, Makoto
• Primary Examiner(s): Rowland, James L.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/525,036
• Time in Patent Office: 741 Days
• Field of Search: 340/630, 340/629, 340/628, 250/573, 250/574, 356/438, 356/439
• US Class Current: 340/630
• CPC Class Codes: G01N 33/0062 concerning the measuring method, e.g. intermittent, or the display, e.g. digital
• CPC Class Codes: G08B 17/103 using a light emitting and receiving device
• CPC Class Codes: G08B 29/185 Signal analysis techniques for reducing or preventing false alarms or for enhancing the reliability of the system

Abstract

A light extinction type smoke detector which uses simple pulsed light or modulation pulsed light to reduce energy consumption, and precisely discriminates smoke generated by fire from extraneous interruption of the light beam from the light source to the photoelectric element to prevent a false alarm.

Claims

1. A light extinction type fire detector, comprising:

a pulsed light-emitting element for emitting pulsed light;

a photoelectric element for generating an output signal in response to light received from said transmitter;

a transmission measurement path for the passage of smoke of a fire to be detected extending between said pulsed light-emitting element and said photoelectric element;

a light path extending from said pulsed light-emitting element across said transmission measurement path to said photoelectric element;

the pulsed light emitted by said pulsed light-emitting element being attenuated by the smoke passing through said transmission measurement path;

a fire-detection circuit connected with said photoelectric element for discriminating whether said output signal of said photoelectric element is lower than a predetermined threshold value and for generating a fire-detection signal when said output signal of said photoelectric element is lower than said predetermined threshold value;

a false-alarm-prevention first time-delay circuit connected with said fire-detection circuit for generating a fire-alarm output signal when said fire-detection circuit generates said fire-detection signal for a first predetermined duration of time;

a second time-delay circuit connected with said fire-detection circuit for generating an inhibit signal when said fire-detection circuit generates said fire-detection signal for a second predetermined duration of time;

said first duration of time being at least as great as said second duration of time;

a light-path-interruption discriminating circuit connected with said photoelectric element for generating a light-path-interrupted signal when said output signal of said photoelectric element is lower than a predetermined threshold value for a third predetermined duration of time;

said third predetermined duration of time being less than said first predetermined duration of time and less than said second predetermined duration of time;

first inhibiting circuit means connected with said light-path-interruption discriminating circuit and with said second time-delay circuit for preventing said light-path-interruption discriminating circuit from generating said light-path-interrupted signal when said second time-delay circuit generates said inhibit signal; and

second inhibiting circuit means connected with said fire-detection circuit and with said light-path-interruption discriminating circuit for preventing said fire-detection circuit from generating said fire-detection signal when said light-path-interruption discriminating circuit generates said light-path-interrupted signal.

2. A light extinction type smoke detector employing pulsed light, comprising:

a pulsed light-emitting element for emitting pulsed light;

a photoelectric element for sensing said pulsed light emitted by said pulsed light-emitting element;

said photoelectric element having an output side;

a transmission measurement path for the passage of smoke of a fire to be detected extending between said pulsed light-emitting element and said photoelectric element;

a light path extending from said pulsed light-emitting element across said transmission measurement path to said photoelectric element;

a peak-value hold circuit for generating a first output signal;

a fire-detection circuit indirectly connected through said peak-value hold circuit to said output side of the photoelectric element for generating a fire-detection signal when said first output signal is lower than a predetermined threshold value;

a light-path-interruption discriminating circuit directly connected to said output side of said photoelectric element;

said light-path-interruption discriminating circuit being provided for discriminating an interruption of said light path when a duration of said interruption attains a first prescribed time interval;

said light-path-interruption discriminating circuit being provided for generating a second output signal when said interruption is discriminated;

said output signal being provided for immediately inhibiting operation of said fire-detection circuit and for simultaneously initiating a light-path-interrupted signal;

said fire-detection circuit being provided for generating a fire-alarm signal when said fire detection signal has endured for a second prescribed time interval;

said fire-alarm signal being provided for inhibiting operation of said light-path-interruption discriminating circuit after a third prescribed time interval has elapsed; and

said first, second and third prescribed time intervals having durations so interrelated that a duration of said second time interval is greater than a duration of said third time interval.

3. A light extinction type smoke detector employing pulsed light, comprising:

a modulated-pulsed light-emitting element for emitting modulated pulsed light;

a photoelectric element for sensing said modulated pulsed light emitted by said pulsed light-emitting element;

said photoelectric element having an output side;

a transmission measurement path for the passage of smoke of a fire to be detected extending between said modulated-pulsed light-emitting element and said photoelectric element;

a light path extending from said modulated-pulsed light-emitting element across said transmission measurement path to said photoelectric element;

an output wave-shaping circuit having an output;

a charge-discharge circuit for said output of said output wave-shaping circuit;

a peak-value hold circuit for generating a first output signal;

a fire-detection circuit indirectly connected through said peak-value hold circuit to said output side of said photoelectric element for generating a fire-detection signal when said first output signal is lower than a predetermined threshold value;

a light-path-interruption discriminating circuit indirectly connected through said output wave-shaping circuit and said charge-discharge circuit to said output side of the photoelectric element;

said light-path-interruption discriminating circuit being provided for discriminating an interruption of said light path when a duration of said interruption attains a first prescribed time interval;

said light-path-interruption discriminating circuit being provided for generating a second output signal when an interruption is discriminated;

said output signal being provided for immediately inhibiting operation of said fire-detection circuit and simultaneously initiating a light-path-interrupted signal;

said fire-detection circuit being provided for generating a fire-alarm signal when said fire-detection signal has endured for a second prescribed time interval;

said fire-alarm signal being provided for interdicting operation of said light-path-interruption discriminating circuit after a third prescribed time interval has elapsed;

said first, second and third prescribed time intervals having durations so interrelated that a duration of said second time interval is greater than a duration of said third time interval.