Dual spectrum frequency responding fire sensor

• US 4,785,292 A
• Filed: 02/11/1987
• Issued: 11/15/1988
• Est. Priority Date: 03/23/1984
• Status: Expired due to Fees

• Current Assignee: Santa Barbara Research Center (Rtx Corporation)
• Original Assignee: Santa Barbara Research Center (Rtx Corporation)
• Inventors: Kern, Mark T., Shamordola, Kenneth A.
• Primary Examiner(s): Swann, III, Glen R.
• Assistant Examiner(s): MULLEN, THOMAS J
• Application Number:
  US07/013,576
• Time in Patent Office: 643 Days
• Field of Search: 340/578, 340/577, 340/600, 250/339, 250/554, 356/315
• US Class Current: 340/578
• CPC Class Codes: F23N 2229/08 detecting flame flicker
• CPC Class Codes: F23N 5/082 using electronic means
• CPC Class Codes: G08B 17/12 Actuation by presence of radiation or particles, e.g. of infrared radiation or of ions

Abstract

Apparatus for sensing the ex(i)stence of a fire and providing a warning, if desired, with improved discrimination against the possibility of false alarms. Dual channel detectors are used, one detector being set to respond to incident radiation having a wavelength in the range of 0.8 to 1.1 microns while the other wavelength range is significantly displaced therefrom, being selected for wavelengths in the range from 14 to 25 microns. Reliability of true signal detection is further improved by the provision of separate flame flicker bandpass filters in the respective channels, these bandpass filters being set for different passbands. Circuits providing ratio discrimination, threshold detectors and delay circuitry are combined with the dual spectrum detectors and disparate flicker frequency filters to achieve improved performance. In addition, the dynamic range of instrument sensitivity is substantially increased by utilizing preamplifiers with wide gain variability controlled by automatic gain control circuits in the dual channel circuitry.

Claims

1. A dual spectrum frequency responding fire sensor comprising:

a first detector for generating electrical signals in response to a range of incident long wavelength radiation;

a second detector for generating electrical signals in response to a range of incident short wavelength radiation substantially displaced from said range of incident long wavelength radiation;

first and second dual path narrowband channel stages coupled in parallel to receive electrical signals generated by said detectors, each of said first and second stages comprising first and second signal paths for processing, respectively, the electrical signals from said first and second detectors;

each of said signal paths including a narrowband filter with the passbands of the filters in said first narrowband channel stage being approximately 2 to 5 Hz and the passband of the filters in said second narrowband channel stage being approximately 6 to 12 Hz; and

logic means connected to combine the outputs of said stages for developing an output signal upon said detectors receiving radiation from a fire source.

2. The sensor of claim 1 wherein the first detector is responsive to radiation have wavelengths in the range of 14 to 25 microns and the second detector is responsive to radiation having wavelengths in the range of 0.8 to 1.1 microns.

3. The sensor of claim 1 wherein a pair of signal paths within a narrowband channel stage includes a ratio comparator stage for receiving signals passed by the narrowband filters, said ratio comparator stage being interconnected to establish a ratio window within which output signals are generated upon receipt of flicker frequency signals passed by said filters.

4. The sensor of claim 3 wherein each signal path includes a threshold comparator for developing an output signal in response to signals passed by said filter along said path which exceed a predetermined threshold level.

5. The sensor of claim 4 further including logic circuit gates connected to receive output signals from said ratio comparators and said threshold comparators and generate a fire signal in response to predetermined output conditions from said comparators.

6. The sensor of claim 1 further including at least one additional narrowband channel stage in parallel with the first and second narrowband channel stages, each of the additional narrowband channel stages having passbands for the narrowband filters therein which are different from the passbands of the narrowband filters in other narrowband channel stages.

7. The sensor of claim 1 further including periodic signal detecting means coupled to the radiation detectors and selectively connected to inhibit one or more of the narrowband stages upon the detection of periodic signal radiation.

8. A dual spectrum frequency responding fire sensor comprising:

a first detector for generating electrical signals in response to a range of incident long wavelength radiation;

a second detector for generating electrical signals in response to a range of incident short wavelength radiation substantially displaced from said range of incident long wavelength radiation;

first and second dual path narrowband channel stages coupled in parallel to receive electrical signals generated by said detectors, each of said first and second stages comprising first and second signal paths for processing, respectively, the electrical signals from said first and second detectors;

each of said signal paths including a narrowband filter having a passband within a predetermined range in which flame flicker frequencies are found, the passbands of the narrowband filters in the signal paths of said first stage being alike but different from and non-overlapping with respect to the passbands of the corresponding narrowband filters in the signal paths of said second stage;

first and second preamplifiers connected respectively in series with said first and second detectors for amplifying electrical signals generated thereby, each of said preamplifiers having a variable gain, and means coupled to the signal paths within one of said channel stages to control the gains of the respective preamplifiers in accordance with signal level in order to increase the maximum sensitivity of the sensor; and

logic means connected to combine the outputs of said stages for developing an output signal upon said detectors receiving radiation from a fire source.