Method and apparatus for laser-based remote methane leak detection
AssigneeHeath Consultants Incorporated
InventorJames M. Rutherford
Life of this patent
Estimating the term…
Abstract
A method and apparatus for remote laser-based detection of gas at levels exceeding natural background levels preferably utilizing wavelength modulated tunable diode laser absorption spectroscopy. In a preferred embodiment, background gas and noise are estimated using statistical moving average and variance calculations. Gas concentration length measurements resulting from the spectroscopy are preferably compared in real-time or near-real-time to the sum of the background and noise estimates and an alarm limit to detect gas presence of concern. Gas levels exceeding this detection threshold are preferably indicated by a prolonged output tone with a pitch indicative of the magnitude of the gas measurement, and gas levels below the detection threshold are preferably indicated by silence.
Claims18
A method of detecting the presence of a gas comprising the steps of,
- illuminating a target with a light beam from a laser having a wavelength generally corresponding to an absorption band of said gas,
- receiving at a detector a received portion of said light beam which is reflected from said target,
- sampling said received portion of said light beam to produce a series of measurements which are indicative of a concentration length product of said gas through which said received portion of said light beam has traveled,
- periodically determining a detection threshold from a statistical analysis of said series of measurements which estimates a threshold level above which a current measurement of said series of measurements is significant,
- comparing said current measurement of said series of measurements with a recent determination of said detection threshold, and
- producing a signal which indicates the presence of said gas at a level greater than said threshold level when said current measurement exceeds the recent determination of said detection threshold.
A method of detecting the presence of a gas comprising the steps of,
- illuminating a target with a light beam from a laser having a wavelength generally corresponding to an absorption band of said gas,
- receiving at a detector a reflected portion of said light beam which is reflected from said target,
- sampling said reflected portion of said light beam into a series of measurements which are indicative of a concentration length product of said gas through which said received portion of said light beam has traveled,
- periodically determining a background gas level estimate by calculating a moving statistical average calculation of a first plurality of said series of measurements,
- periodically determining a measurement noise level estimate from a moving statistical variance calculation of a second plurality of said series of measurements,
- providing a user determined alarm limit,
- comparing a current measurement of said series of measurements with a function of a sum of a recent determination of said background gas level estimate, a recent determination of said measurement noise level estimate and said alarm limit, and
- indicating the presence of said gas when said current measurement of said series of measurements exceeds said function of said sum by a predetermined threshold.
An apparatus (11) for detecting the presence of a gas (20) comprising,
- a laser (30) capable of emitting light (18) characterized by a wavelength generally corresponding to an absorption band of said gas,
- an optical detector (32) capable of measuring said light disposed near said laser and positioned to receive a portion (24) of said light emitted by said laser and that is reflected back thereto by a distant target (22),
- a signal processing module (34) operatively coupled to an output of said optical detector and designed and arranged to produce a series of discreet measurements indicative of the concentration length product of the gas through which said portion of said light has traveled,
- a statistical detection processor module (50) operatively coupled to an output of said signal processing module and designed and arranged to statistically calculate a gas background estimate, and a measurement noise estimate, and to differentiate which of said measurements exceeds a sum of said gas background estimate and said measurement noise estimate, and a user provided alarm limit, and
- a user interface (38) operatively coupled to an output of said detection processor module.
Dependencies are inferred from the claim text.