US 5,625,342 A · Plural-wavelength flame detector that discriminates between direct and reflected radiation

Abstract

A flame detector employs a plurality of wavelength selective radiation detectors and a digital signal processor programmed to analyze each of the detector signals, and determine whether radiation is received directly from a small flame source that warrants generation of an alarm. The processor's algorithm employs a normalized cross-correlation analysis of the detector signals to discriminate between radiation received directly from a flame and radiation received from a reflection of a flame to insure that reflections will not trigger an alarm. In addition, the algorithm employs a Fast Fourier Transform (FFT) frequency spectrum analysis of one of the detector signals to discriminate between flames of different sizes. In a specific application, the detector incorporates two infrared (IR) detectors and one ultraviolet (UV) detector for discriminating between a directly sensed small hydrogen flame, and reflections from a large hydrogen flame. The signals generated by each of the detectors are sampled and digitized for analysis by the digital signal processor, preferably 250 times a second. A sliding time window of approximately 30 seconds of detector data is created using FIFO memories.

Claims20

Dependent claims

A flame detector apparatus comprising:

a) first and second radiation responsive detectors, said first radiation responsive detector being responsive to radiation of a first wavelength and said second radiation responsive detector being responsive to radiation of a second wavelength, wherein said first and second wavelengths are present in radiation from a flame to be detected, but are reflected differently off of a reflective surface, each said detector generating a signal in response to detected radiation;
b) processor means for analyzing the signals generated by said first and second detectors, and determining therefrom whether radiation detected by said first and second detectors is received directly from a flame, or is received from a reflection of a flame, said processor means including means for generating an alarm signal if it is determined that radiation detected by said first and second detectors is received directly from a flame;
and
c) alarm indicator means responsive to said alarm signal for indicating that a flame has been detected.

1 more element

A flame detector apparatus comprising:

a) a first infrared detector being responsive to radiation of a first infrared wavelength and generating a first analog electrical signal in response thereto;
b) an ultraviolet radiation detector being responsive to ultraviolet wavelength radiation and generating a second analog electrical signal in response thereto;
c) an A/D converter for periodically sampling said first and second analog electrical signals, and converting them to first and second digital sample values, respectively;
d) a digital signal processor for receiving said first and second digital sample values, and calculating the normalized cross-correlation of said first and second digital sample values to determine whether radiation detected by said first and second detectors is received directly from a flame or from a reflection of a flame, said digital signal processor including means for generating an alarm signal if the calculated normalized cross-correlation exceeds a threshold value which indicates that radiation detected by said first and second detectors is received directly from a flame;
and
e) alarm indicator means responsive to said alarm signal for indicating that a flame has been detected.

3 more elements

A method for detecting a flame which discriminates between a directly detected flame, and the reflection of a flame, said method comprising:

a) selecting a plurality of radiation wavelengths which are all present in a flame to be detected, but which have different reflection characteristics;
b) providing a plurality of wavelength selective radiation detectors, each said detector being responsive to radiation of a corresponding one of said plurality of wavelengths, and generating an electrical signal in response thereto;
c) positioning said plurality of detectors to receive radiation from an area in which a flame is to be detected;
d) calculating the normalized cross-correlation of each pair of detector signals;
e) comparing the value of said calculated normalized cross-correlation of each pair of detector signals to a threshold value above which indicates that the radiation detected by said plurality of detectors is received directly from a flame, and not from a reflection of a flame;
and
f) generating an alarm indication if the normalized cross-correlation value of at least one pair of detector signals exceeds said threshold value.

4 more elements

Dependencies are inferred from the claim text.

Plural-wavelength flame detector that discriminates between direct and reflected radiation

Life of this patent

Plural-wavelength flame detector that discriminates between direct and reflected radiation

Life of this patent

Abstract

Claims20