78 results about "Wavelength modulation spectroscopy" patented technology

The invention belongs to the technical field of gas detection and relates to a laser infrared gas analyzer based on TDLAS-WMS (tunable diode laser absorption spectroscopy-wavelength modulation spectroscopy) for detecting hydrogen chloride, methane, carbon monoxide, water vapor and other gases. The laser infrared gas analyzer comprises a laser, a laser driving circuit, a temperature control circuit, an optical system with an optical cavity, a main detector, a reference detector, an intensity modulation and canceling circuit, a phase-locking and amplification circuit and a data acquisition and display circuit, wherein the laser driving circuit and the temperature control circuit are used for controlling the laser to emit light, the two ends of the optical system are respectively connected with the laser and the detector, the intensity modulation and canceling circuit is used for canceling the influence of intensity modulation in the system, the phase-locking and amplification circuit is used for extracting harmonic signals, and the data acquisition and display circuit is used for displaying the concentration of the gas to be detected. Compared with other detection instruments, the laser infrared gas analyzer has the advantages that division operation is introduced into the intensity modulation and canceling circuit, and the laser infrared gas analyzer is combined with a space double-optical path differential detection method, so that the influence of the intensity modulation can be fundamentally canceled.

The invention relates to a gas parameter online measurement method based on wavelength modulation spectroscopy and belongs to the field of tunable diode laser absorption spectroscopy. According to the method, a gas absorptivity function is fitted by using an odd number of harmonic signals of an X axis and a Y axis output by a phase-locked amplifier based on the wavelength modulation spectroscopy, normalization processing is carried out on the harmonic signals of the X axis and the Y axis by using first harmonic background signals so as to eliminate the influence of factors, such as background signal, laser intensity and modulation factor, and then, the temperature, concentration, pressure and spectroscopic constant of gas are directly measured by using the gas absorptivity function. The gas parameter online measurement method based on the wavelength modulation spectroscopy has the advantages that the problem that the wavelength modulation spectroscopy needs to calibrate experimental measuring temperature and concentration and cannot measure the pressure and spectroscopic constant of gas nowadays is solved, and the application range of the wavelength modulation spectroscopy is widened.

This specification discloses a method and apparatus for the mobile and remote detection of a gas, such as methane, in the atmosphere. The apparatus includes a TDL based Light Detection and Ranging (LIDAR) driven at carrier frequency lying within the absorption line of the gas. The apparatus also drives the TDL with a modulation frequency to generate upper and lower sidebands in the output of the TDL and with a low ramp frequency to sweep the output of the TDL across twice the width of the pressure-broadened absorption line of the gas, preferably the first overtone absorption line in the case of methane detection. The apparatus include reference and calibration cells or chambers, and includes a light collector and detectors to detect the quantity and modulation of the light that passes the reference or calibration cells and that is received by the apparatus after reflection back toward the apparatus from an uncooperative target. The apparatus further includes a signal processor that applies a derivative spectroscopy technique, such as frequency modulation spectroscopy or wavelength modulation spectroscopy, to determine the presence of the gas in the atmosphere.

The invention relates to a gas temperature and concentration online measuring method based on a first harmonic signal, which belongs to the technical field of tunable diode laser absorption spectrum (TDLAS). Online measurement of the gas temperature and concentration is realized through the relation between a first harmonic X-axis signal and a first harmonic Y-axis signal and a gas absorption rate functional integral value. The advantages of a direct absorption method in the TDLAS technology are combined with the wavelength modulation method, so that not only is the difficulty that the direct absorption method cannot be applied in a worse environment and a weak absorption condition solved, but also the difficulty that the gas temperature and the gas concentration are determined through a calibration experiment in the measurement of the wavelength modulation method can be solved. Due to the adoption of the method, the measurement precision of the TDLAS technology in the industrial field can be effectively improved, and the application range can be enlarged.

The invention relates to a device, a method and a system for determining a road surface condition, where the surface condition is one of dry, wet or icy. The device comprises a reflectance spectrometer which senses the reflectance properties of the road at one or several wavelengths and uses these reflectance properties to determine the surface condition. The reflectance spectrometer is a wavelength modulation spectrometer, preferably for the near infrared region. The system determines the surface condition and indicates it to a user of the system.

Methods and systems to measure simultaneously concentrations or concentration ratio(s) of two or more gas ingredients in a sample area comprising: a wavelength modulated light source; an acoustic detector or a photodetector; and means to analyze the signal from the acoustic detector or the photodetector and calculate the concentrations or concentration ratio(s). The light from the light source is transmitted through the sample area. Part of the light will be absorbed in the sample area by the gas ingredients and generates photoacoustic signal. The acoustic detector is used to sample the photoacoustic signal. Alternatively, a photodetector is used to sample the light intensity after the light is transmitted through the sample area.

The invention discloses a method combining hyper-spectrum and wavelength modulation for simultaneous measurement of high-temperature gas two-dimensional transient temperature field and concentration field. The method includes: arranging a laser array in a to-be-measured high-temperature area, and conducting hyperspectral scanning on the to-be-measured area to obtain water vapor absorption spectral line information, and carrying out demodulation with a digital phase lock technology to obtain each harmonic signal, then conducting background deduction first harmonic normalization processing, extracting the maximum amplitude value of the signal to measure regional temperature field and water vapor concentration field, and during measuring, conducting grid discretization treatment on the to-be-measured area, arranging laser beam at each row and each column of the grid to conduct broad spectrum scanning on the characteristic spectral line of the to-be-measured gas under a wavelength modulation mode, and using intelligent optimization algorithm to realize inversion of the temperature field and gas concentration field. The measurement method provided by the invention combines hyper-spectrum and wavelength modulation spectroscopy technologies, and is especially suitable for monitoring of high-temperature gas two-dimensional temperature field and concentration field on harsh industrial sites.

A method of calibration-free scanned-wavelength modulation spectroscopy (WMS) absorption sensing is provided by obtaining absorption lineshape measurements of a gas sample on a sensor using 1/-normalized WMS-2/j where an injection current to an injection current-tunable diode laser (TDL) is modulated at a frequency ̂ where a wavelength modulation and an intensity modulation of the TDL are simultaneously generated, extracting using a numerical lock-in program and a low-pass filter appropriate band-width WMS-<</ (n=1, 2, . . . ) signals, where the WMS-<</ signals are harmonics of the f, determining a physical property of the gas sample according to ratios of the WMS-<</ signals, determining the zero-absorption background using scanned-wavelength WMS, and determining non-absorption losses using at least two the harmonics, where a need for a non-absorption baseline measurement is removed from measurements in environments where collision broadening has blended transition linewidths, where calibration free WMS measurements without knowledge of the transition linewidth is enabled.

Several methods of calibrating a wavelength-modulation spectroscopy apparatus configured to measure a concentration of an analyte in a sample gas are disclosed. Each of the methods allows for calibration and recalibration using a relatively safe gas regardless of whether the sample gas for which the concentration of the analyte can be determined is a hazardous gas. In one embodiment of the invention, calibration that is sample-gas specific is accomplished by determining a first slope coefficient and calibration function for the sample gas, after which a scaling factor can be determined based on the first slope coefficient and a second slope coefficient for the same or a different sample gas and used in a subsequent calibration (or recalibration) to scale the calibration function. In other embodiments of the invention, calibration that is not sample-gas specific is accomplished to allow for the determination of the analyte concentration in variable gas compositions and constant gas compositions.

The invention relates to a flue gas content laser on-line detection method and a system. The system provided by the invention comprises a photic driving unit, a light emitting unit, an optical signal detection unit, an electric signal transmission unit, a central control cabinet and an industrial control computer. The method provided by the invention comprises the following steps of: allowing double-frequency modulated laser to pass through a background gas and then pass through a spectroscope, directly receiving the reflected laser by a photo-detector, allowing the laser which passes throughthe spectroscope to travel through flue gas and to be received by another photo-detector; and processing electric signals outputted from the two photo-detectors to obtain the detection signal. By theadoption of the sensing structure of two light beams, the wavelength modulation spectrum technology and the phase lock amplification technology, the technical issue of measurement accuracy by presentoptical gas sensors is improved.

The invention belongs to the technical field of laser spectroscopy, and mainly relates to a calibration-free wavelength modulation spectroscopy gas detection method based on an S[2f] method. Corresponding scientific analysis shows that A, i[1], i[2], concentration and phase difference psi[1] and psi[2] have little influence on S[2f]/S[2f]<c> signals, and only WMRF has obvious influence on the S[2f]/S[2f]<c> signals. Therefore, under conditions of uncertain concentration and phase shift, WMRF is obtained by inverting the S[2f]/S[2f]<c> signals, and because fitting parameters are greatly reduced, the method can be guaranteed to be simple, rapid and accurate. On the basis, the concentration of to-be-measured gas is fitted, and a measurement value with higher accuracy degree is obtained. The new method is simple, rapid and accurate, and is suitable for wide promotion in the field of gas detection.

The invention discloses a gas absorptivity online measurement method based on fast Fourier transform, and belongs to the technical field of tunable diode laser absorption spectroscopy (TDLAS). According to the method, a sine wave is adopted to modulate the output wavelength of a tunable semiconductor laser, a characteristic frequency spectrum containing absorption information is extracted throughfast Fourier transform on the transmission light intensity, the transmission light intensity is reconstructed, and other frequency noise signal interferences such as particulate matter and light intensity fluctuation can be effectively eliminated; a relationship between the laser light intensity and the wavelength is established based on an intermediate variable eta, and the transmission light intensity obtained by reconstruction is fitted with eta as an independent variable to realize synchronous online measurement of the incident light intensity and the gas absorptivity. The method is simpleand convenient to operate and wide in application range; the problems that a direct absorption method is large in base line fitting uncertainty and a wavelength modulation method cannot accurately measure the absorptivity are solved, and the gas absorptivity measurement precision is effectively improved.

A method in which the wavelength of the light of a tunable light source is varied periodically over an absorption line of interest for the gas component to measure the concentration of a gas component in a measurement gas based on one of two measurement methods of direct absorption spectroscopy and wavelength modulation spectroscopy and, where in the case of wavelength modulation spectroscopy, the wavelength of the light is additionally sinusoidally modulated at a high frequency and with a small amplitude, where the intensity of the light is detected after transradiation of the measurement gas and processed to yield a measurement result, and where in order to increase the accuracy and reliability of the measurement, the two measurement methods are applied simultaneously during each period, or alternately in consecutive periods, and their results are combined by averaging to form the measurement result.

A computer-implemented method for measuring gas concentration from a 2f signal in wavelength modulation spectroscopy is presented. The computer-implemented method includes emitting a beam of light from a laser to pass through a gas sample, calculating a gas measurement value from the gas sample via a trough distance calculator using a trough distance of a gas absorption line's 2f signal, calibrating the gas measurement value via a multi-point calibration process, and outputting the gas measurement value to a user interface of a computing device.

The invention belongs to the technical field of laser spectroscopy, in particular relates to a WMRF new model-based calibration-free wavelength modulation spectrum gas detection method, and solves the technical problem of low precision of a calibration-free wavelength modulation spectrum technology currently used for gas concentration detection. An etalon of a 0.02 cm<-1> free spectral range is used to analyze wavelength change WMRF caused by signal modulation, a first harmonic component with the amplitude linearly changed and a second harmonic component with an amplitude as a constant are observed, and a new model for describing WMRF is described. By using the new model, a system can acquire a more accurate fitting result; compared with a conventional system, hardware module addition and manual operation are not needed, only program improvement is needed, and development and application are facilitated. The method is simple in technical scheme and convenient in operation, consumption of lots of manpower and material resources is not needed, and the cost and convenience degree in use are easily accepted by most application departments.

The invention discloses a harmonic wavelet analysis method for modulating spectral signals. The harmonic wavelet analysis method is based on the wavelength of a TDLAS, and includes the implementation steps of (1) building a harmonic wavelet equation of the modulated spectral signals of the TDLAS, (2) computing the harmonic wavelet expansion coefficients of the signals with a decomposition algorithm, (3) determining decomposition layer numbers required by signal analysis according to the corresponding relation between wavelet decomposition layer numbers and analysis frequency bands, (4) retaining the harmonic wavelet coefficients of the required frequency bands, and obtaining the signals of the frequency bands through Fourier transformation, (5) constructing an envelope function of the frequency bands, and (6) carrying out an envelope taking process on the signals of the frequency bands to obtain frequency doubling signals of the modulated signals of the TDLAS.