Fire detector

• US 6,166,647 A
• Filed: 01/18/2000
• Issued: 12/26/2000
• Est. Priority Date: 01/18/2000
• Status: Expired due to Fees

• Current Assignee: Jaesent Incorporated
• Original Assignee: Jaesent Incorporated
• Inventors: Wong, Jacob Y.
• Primary Examiner(s): Wu, Daniel J.
• Assistant Examiner(s): NGUYEN, HUNG T
• Application Number:
  US09/484,853
• Time in Patent Office: 343 Days
• Field of Search: 340/628, 340/627, 340/632, 340/629, 340/630, 340/522
• US Class Current: 340/628
• CPC Class Codes: G08B 17/10 Actuation by presence of smoke or gases , e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means

Abstract

An improved fire detector is obtained by combining a conventional smoke particle sensor with a fire radicals odor sensor; the latter being an electronic nose tuned to respond to the presence of a family of radicals, produced by most fires, that is responsible for the odor associated with a fire. The conventional smoke particle sensor is prevented from producing an alarm signal unless the tuned electronic nose senses that the fire-produced radicals are increasing at a rate that exceeds a preset threshold rate. In another aspect of the invention, the smoke particle sensor is provided with a second, lower, threshold connected to a timer so that an alarm will be produced if the lower threshold is exceeded, without interruption, for a preset time. The improved fire detector, using the combined sensors, has greater sensitivity and a lower false alarm rate.

Claims

1. A method for reducing false alarms in a fire detector of a type in which an alarm signal is generated when the output signal of a smoke sensor exceeds a preset threshold, said method comprising the steps of:

adding to the fire detector a fire radicals sensor that produces a fire radicals concentration signal;

determining the rate of change of the fire radicals concentration signal; and

,

inhibiting the alarm signal so long as the rate of increase of the fire radicals concentration signal remains below a preset threshold.

2. A fire detector for producing an alarm signal with a low false alarm rate, comprising:

a smoke sensor for producing an output signal responsive to the presence of smoke;

smoke threshold means connected to said smoke sensor for receiving the output signal of said smoke sensor and for producing an output signal when the output signal of said smoke sensor exceeds a preset level;

a fire radicals sensor for producing an output signal responsive to the presence of fire radicals;

rate means connected to said fire radicals sensor for receiving the output signal of said fire radicals sensor and for producing an output signal representative of the rate of change of the output signal of the fire radicals sensor;

fire radicals rate threshold means connected to said rate means for receiving the output signal of said rate means and for producing an output signal when the output signal of said rate means exceeds a preset level; and

,

logic means connected to said smoke threshold means and connected to said fire radicals rate threshold means, and producing an alarm signal only when both the output signal of said smoke threshold means and the output signal of said fire radicals rate threshold means are present simultaneously;

whereby, a low false alarm rate is achieved by inhibiting the smoke sensor from producing the alarm signal unless the fire radicals are increasing at a preset rate.