Photoelectric smoke sensing and alarming device

• US 4,297,688 A
• Filed: 01/02/1980
• Issued: 10/27/1981
• Est. Priority Date: 09/30/1977
• Status: Expired due to Term

• Current Assignee: Cybernet Electronic Corp.
• Original Assignee: Cybernet Electronic Corp.
• Inventors: Kakigi, Takao
• Primary Examiner(s): Caldwell, Sr., John W.
• Assistant Examiner(s): Myer, Daniel
• Application Number:
  US06/109,145
• Time in Patent Office: 664 Days
• Field of Search: 340/630, 250/573, 250/574, 250/575, 250/564, 250/577, 356/438, 356/439
• US Class Current: 340/630
• CPC Class Codes: G08B 17/107 for detecting light-scattering due to smoke

Abstract

A photoelectric smoke sensing and alarming device capable of discriminating the smoke generated by a fire from other smokes such as cigarette smoke. The device has a chamber into which the smoke is introduced. The chamber accommodates a light-emitting element adapted to emit a light beam in the form of pulses and a light-receiving element sensitive to the scattering of light due to the presence of the smoke in the chamber. The output from the light-receiving element is delivered to an amplifier which in turn delivers an output to a gate circuit having a level comparator adapted to compare the level of the output from the amplifier with a reference sensing level. Means are provided for actuating an alarming circuit only when more than two successive pulses of level exceeding the reference sensing level are generated.

Claims

1. A photoelectric smoke sensing and alarming device of a type having a pulse generator, a chamber, a light emitting element disposed in said chamber and adapted to emit a light beam in the form of pulses in cooperation with said pulse generator, and a light-receiving element disposed in said chamber and adapted to receive the light from said pulses of light beam, so as to sense the presence of smoke in said chamber through a detection of scattering of said light beem caused in said chamber by said smoke, comprising:

an amplifier having gain control and connected to said light-receiving element for producing an output upon reception of light by said light-receiving element;

a threshold detecting comparator for producing a pulse output when the output of said amplifier exceeds a predetermined threshold level;

a delay circuit coupled to the pulse generator for producing a delayed pulse output in synchronism with the output of the comparator;

a gate circuit having a pair of inputs respectively connected to the output of the comparator and the output of the delay circuit for delivering a first output upon simultaneous receipt of output pulses from said comparator and said delay circuit and for producing a second output upon the occurrence of the delayed output pulse of the delay circuit in the absence of the output pulse of said comparator; and

a flip-flop circuit coupled to said gate circuit and adapted to be set by the first output from said gate circuit, wherein an alarm is generated over a time length which is at least as long as the time between successive of said pulses generated by said pulse generator, only when at least n (n>

2) successive of said first outputs are delivered by said gate circuit to said flip-flop circuit, said second output of said gate circuit being used to reset the flip-flop circuit in the absence of successive first output signals from said gate circuit.