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

US5625342A · kind A · utility

Assignee

• The United States of America as represented by the Administrator of the National Aeronautics and Space Administration · US

Inventors

• Gregory H. Hall · Rockledge, US
• Heidi Barnes · Forestville, US
• Pedro J. Medelius · Merritt Island, US
• Howard J. Simpson · Melbourne, US
• Harvey S. Smith · Engelenbeemden, US

Key dates

• Filing date: Nov 6, 1995
• Grant date: Apr 29, 1997
• Expiry date: Nov 6, 2015

Classification

• Technology area (CPC F): Mechanical Engineering; Lighting; Heating
• CPC primary: F23N2229/16
• WIPO field: Control
• WIPO sector: Instruments

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…