Download or read book Development of a Two tone Frequency Modulation Tunable Diode Laser Absorption Spectrometer TTFM TDLAS for Measuring Methane Fluxes written by and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Application of Tunable Diode and Other Infrared Sources for Atmospheric Studies and Industrial Process Monitoring II written by Alan Fried and published by SPIE-International Society for Optical Engineering. This book was released on 1999 with total page 276 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Near infrared Tunable Diode Laser Absorption Spectrometer for Trace Gas Detection written by Iain Fletcher Howieson and published by . This book was released on 1997 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Meteorological and Geoastrophysical Abstracts written by and published by . This book was released on 1993 with total page 512 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Wavelength Modulation Spectroscopy with Tunable Diode Lasers written by Kevin Duffin and published by . This book was released on 2007 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Tunable diode laser spectroscopy (TDLS) has become the preferred option for industrial gas monitoring. TDLS with direct detection provides absolute measurement of a rotational / vibrational gas absorption line transmission function, facilitating the extraction of gas concentration (from line strength measurement). TDLS with wavelength modulation spectroscopy (WMS) enables AC detection of absorption line derivatives at frequencies where laser and 1/f noise is reduced. Coupled with lock-in detection, this provides a sensitivity improvement of up to 2 orders of magnitude. At fixed temperature and pressure, calibration to signals measured on a known gas composition has been used successfully to determine system scaling factors. However, demand has grown for gas monitoring in environments where the gas pressure is constantly varying and unknown. This introduces significant errors in the analysis as the primary system scaling factor is a function of linewidth, which is varying with the unknown pressure. Errors also arise from the inaccuracies in determining a number of instrument scaling factors, including the AM and FM characterisation of the laser. Pressure measurements may be made and the errors in concentration corrected, if the gas absorption linewidth can be accurately measured from the recovered signals and the instrument scaling factors can be accurately determined. However, the lack of accurate in-situ wavelength referencing schemes for use in the field, make linewidth measurement extremely difficult. Add to this the fact that conventional TDLS / WMS measurements are prone to systematic interference and the errors accumulated from inaccurate instrument scaling (noted above) and linewidth measurement, could determine a large final error on the derived concentration and / or pressure. This work reports the proposal, development and validation of both an in-fibre wavelength referencing scheme and a new technique for measuring the absolute absorption line transmission function using TDLS with WMS. Measuring the absolute absorption line transmission profile, as a function of the laser's wavelength scan across the absorption line, facilitates the extraction of the gas concentration and pressure via comparisons to theory (based on HITRAN data). Through novel signal processing techniques, the approach is free from systematic distortion and is absolute without the need for calibration. This new approach provides many of the benefits of TDLS / WMS, whilst offering the simplicity and accuracy of TDLS with direct detection. The promising results show that we have significantly advanced TDLS technology towards realising a stand-alone instrument for determining accurate gas composition measurements in harsh industrial environments.
Download or read book Dual beam Second derivative Tunable Diode laser Infrared Spectroscopy Applied to Trace gas Measurement written by and published by . This book was released on 1981 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A dual beam diode laser spectrometer has been constructed using off-axis reflective optics. The spectrometer can be amplitude modulated for direct absorption measurements or frequency modulated to obtain derivative spectra. The spectrometer has high throughput, is easy to operate and align, provides good dual beam compensation, and has no evidence of the interference effects that have been observed in diode laser spectrometers using refractive optics. Unpurged, using second derivative techniques, the instrument has measured 108 parts-per-million CO (10 cm absorption cell, atmospheric pressure-broadened) with good signal/noise. With the replacement of marginal instrumental components, the signal/noise should be substantially increased. This instrument was developed to monitor the evolution of decomposition gases in sealed containers of small volume at atmospheric pressure.
Download or read book Use of Diffuse Reflections in Tunable Diode Laser Spectroscopy written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Tunable diode laser absorption spectroscopy (TDLAS) is an optical gas sensing technique in which the emission frequency of a laser diode is tuned over a gas absorption line of interest. A fraction of the radiation is absorbed by the sample gas and this can be determined from measurements of initial intensity and the intensity transmitted through the sample. The amount of light absorbed is related to the gas concentration. Additional modulation techniques combined with phase sensitive detection allow detection of very low gas concentrations (several parts per million). The advantages of using TDLAS for trace gas sensing include; fast response times, high sensitivity and high target gas selectivity. However, the sensitivity of many practical TDLAS systems is limited by the formation of unintentional Fabry-Perot interference fringes in the optical path between the source and detector. The spacing between the maxima of these fringes, in particular those generated in gas cells, can be in the same wavelength range as Doppler and pressure-broadened molecular line widths. This can lead to (1) interference fringe signals being mistaken for gas absorption lines leading to false concentration measurements or (2) distortion or complete obscuring of the shape and strength of the absorption line, such that the sensitivity of the instrument is ultimately limited by the fringes. The interference fringe signals are sensitive to thermal and mechanical instabilities and therefore can not be removed by simple subtraction techniques. Methods that have been proposed by previous workers to reduce the effects of interference fringes include careful alignment of optical components and/or mechanically jittering the offending components. In general the alignment of the optical components is critical. This often leads to complex and fragile designs with tight tolerances on optical component alignment, and can therefore be difficult and expensive to maintain in field instruments. This thesis pr.
Download or read book Development of a Tunable Diode Laser Absorption Spectroscopy Technique for Application to Tomographic Measurements in Scramjets written by Marc Gareth Sharma and published by . This book was released on 2010 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Principles and development of tunable diode laser spectroscopy for measuring fluxes of ammonia and nitric acid written by M M. Twigg and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Tunable Diode Laser Absorption Spectroscopy for Trace Gas Measurements with High Sensitivity and Low Drift written by Christoph Dyroff and published by . This book was released on 2009 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book discusses the mechanical and opto-electronic design of laser spectrometers for measuring two very important atmospheric gases, namely water vapor and its isotopic ratios, and formaldehyde. For measuring water vapor, shot-noise limited sensitivity has been achieved by a careful choice of system components and data processing. For measuring formaldehyde, a selective sample modulation exploiting the Stark effect has been used to greatly improve the sensitivity.
Download or read book In Situ Probe enabled Tunable Diode Laser Absorption Measurements in Flames Shock Tubes and Shock Tunnels written by Julian Jon-Laurent Girard and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Spectroscopic measurement strategies enabled by in situ laser-based probes were implemented in low-pressure flames, shock tubes, and a hypersonic reflected shock tunnel. In particular, tunable diode laser absorption spectroscopy (TDLAS) was leveraged to accurately infer quantities of interest such as temperature, species concentration, and pressure. Targeted environments spanned both flowing and static samples, reacting and inert compositions, and varying degrees of thermal equilibrium. Two bodies of work falling under this general theme of research are presented. First, two applications of a single-ended optical probe that incorporates a mid-infrared (MIR) CO2 TDLAS diagnostic are summarized. The rovibrational CO2 diagnostic, with transitions centered near 4.2 um, was developed for sensitive two-line thermometry in combustion environments, optimal in the temperature range of 1200 -- 2100 K and the pressure range of 0 - 2 atm. The selected transitions correspond to the strong v3 asymmetric stretch mode of CO2, whose fundamental band boasts the strongest MIR lines among common combustion products (i.e. CO2, CO, H2O, OH, NO). In the first application of this diagnostic, an interband quantum cascade laser (ICL) was directed across a low-pressure burner-stabilized flame using a single-ended optical probe composed of two thin sapphire rod waveguides. Probe-based measurements of temperature and CO2 mole fraction were collected in flames of 25 torr and 60 torr total pressure, and at distances from the burner surface in the range of 3 - 23 mm. In another study, this CO2 diagnostic with a similar single-ended probe implementation was applied to shock tube experiments. The shock tube endcap probe developed enables measurements of relevant reflected-shock region (region 5) quantities (e.g. temperature and CO2) at variable distances from the shock tube endwall, and offers an alternative path length option to traditional sidewall optical portholes. TDLAS measurements of temperature and CO2 mole fraction made with the endwall probe were typically subject to uncertainties of 1% and 5%, respectively. The sensor performance was validated in inert shocked mixtures with 1 - 7% CO2 diluted in argon or nitrogen, and spanning the temperature range of 1200 - 2000 K and pressure range of 0.7 - 1.2 atm. Probe-based measurements were compared directly with traditional sidewall window measurements (i.e. full tube diameter path length) and empirically supported simulations. Finally, perturbation of region 5 conditions by the probe was assessed with a series of tests. The main body of work discussed in this thesis concerns a series of studies conducted at the T5 reflected shock tunnel located at the California Institute of Technology. The focus of these experiments was to conduct spectroscopic measurements of various species in hypersonic nonequilibrium air flows generated at the facility, in support of freestream and flow-model investigations. Freestream characterization of T5 was conducted through two iterative efforts, first involving quasi-quantitative path-averaged measurements of nitric oxide (NO) across the entire (nonuniform) test section. In a subsequent effort, a custom flow-cutting optical probe was used to measure absorbing rovibrational NO transitions in the (uniform) core flow of the freestream. Measured quantities included NO rotational and vibrational temperature, partial pressures of NO, CO, H2O, K, and flow velocity. During this set of experiments, the uniformity of the measured quantities across the core and beyond was assessed by repeating the experiment with distinct probe lengths (i.e. different optical path lengths). Finally, NO, CO and electronically excited oxygen absorption were measured at spatially-precise locations in the post-shock flow generated around a cylindrical model. The path-averaged measurements were processed to infer post-shock quantities of interest, using simple models of the pathwise condition distribution. Insights are drawn by comparing these preliminary measurements with existing 3D CFD simulations of the cylinder post-shock flowfield.
Download or read book Industrial Applications of Tunable Diode Laser Absorption Spectroscopy written by Zhenzhen Wang and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Tunable diode laser absorption spectroscopy (TDLAS) utilizes the absorption phenomena to measure the temperature and species concentration. The main features of the TDLAS technique are its fast response and high sensitivity. Extensive research has been performed on the utilization of diode laser absorption spectroscopy for the system monitoring and its control. The TDLAS technique gives self-calibrations to reduce the noise such as particles and dusts because the laser wavelength is rapidly modulated at kHz rates. In addition, two dimensional (2D) temperature and concentration distributions can be obtained by combining computed tomography (CT) with TDLAS. The TDLAS applications have been extensively studied with great progress. This chapter largely focuses on the engineering fields, especially the practical industrial applications.
Download or read book Near Infrared Tunable Diode Laser Spectroscopy for Aero Engine Related Applications written by James R. P. Bain and published by . This book was released on 2012 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Tunable diode laser spectroscopy is a widely used technique for recovering quantitative gas information in a range of industrial applications. Established methods often use readily available, robust and low cost optoelectronic hardware in the near-infrared, with output wavelengths that coincide with the absorption spectra of several important gas species of interest, providing a versatile platform for gas analysis instrumentation. In this work the challenges associated with the recovery of gas information from harsh detection environments, particularly for aero engine diagnostics, are considered. For stand-alone instrumentation, calibration-free direct absorption measurements are highly advantageous yet calibrated techniques employing wavelength modulation spectroscopy are often favoured due to their significantly higher sensitivities. Recent developments have enabled calibration-free line shape recovery using lock-in amplifier detection of the residual amplitude modulation in wavelength modulated signals. These techniques have significant potential in harsh environments, but the overall sensitivity is limited by distortions to the recovered line shapes at high modulation amplitudes and by large background signals that saturate the detection electronics. In this thesis, solutions to these two problems are proposed, investigated and validated. A correction function is derived that is able to account for line shape distortions at arbitrarily high modulation indices. Application of the function depends upon knowledge of the experimental modulation index and two methods for extracting this information directly from the experimental signals are described. The full correction procedure has been experimentally validated. An investigation was made into the use of autobalanced photoreceivers, typically used for common mode noise cancellation, for direct absorption measurements and in a different configuration for nulling of the residual amplitude modulation (RAM) in wavelength modulation spectroscopy. Initial measurements suggest that removal of the background RAM can increase the lock-in detection sensitivity by over an order of magnitude. In addition an external amplitude modulator has been iv shown to be an effective method for producing sensitive absorption signals that are free of distortions, recoverable at frequencies that are outside the bandwidth of most environmental noise sources. A temperature sensor based on ratio thermometry of ambient water vapour absorption was designed and evaluated. The sensor is intended to provide accurate intake gas temperature information during aero engine ground testing when misting conditions prevent standard thermocouples from providing reliable data. Direct detection and second harmonic wavelength modulation spectroscopy experiments were undertaken in an environmental chamber, over the range 273-313K, to test the potential accuracy of the proposed system. Using a second harmonic peak height method, temperature information based on a calibration was able to recover temperature measurements with precision of ±0.4K however the overall accuracy suffered from a problematic calibration drift. Three engine test campaigns are described in which a range of recovery methods and potential optical system layouts are evaluated for the purposes of intake and exhaust mounted test bed sensor systems. The effects of extreme noise conditions were observed on a variety of measurements and favourable detection and modulation options were identified for the purpose of planning proposed future engine tests. Exhaust plume measurements of high temperature water vapour on the Rolls-Royce Environmentally Friendly Engine demonstrator established the viability of temperature and concentration measurements up to 850K.
Download or read book Wavelength modulation Spectroscopy for Determination of Gas Properties in Hostile Environments written by Christopher S. Goldenstein and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the past 40 years, tunable diode laser absorption spectroscopy (TDLAS) sensors have matured into a practical technology for providing non-intrusive, in-situ measurements of gas properties in a number of hostile energy systems. However, the applicability of TDLAS sensors has been limited by a number of fundamental measurement challenges including: beam-steering, non-absorbing transmission losses, interfering emission, line-of-sight non-uniformities, and broad and blended absorption spectra at high pressures. This work presents the development and demonstration of several novel calibration-free wavelength-modulation spectroscopy (WMS) techniques and sensors that enable high-fidelity measurements of gas properties in highly non-uniform gases and high-pressure gases. These WMS techniques are demonstrated with measurements of gas temperature, H2O, pressure, and velocity in two model scramjet combustors and a pulse detonation combustor.
Download or read book Directory of Graduate Research written by and published by . This book was released on 2001 with total page 1850 pages. Available in PDF, EPUB and Kindle. Book excerpt: Faculties, publications and doctoral theses in departments or divisions of chemistry, chemical engineering, biochemistry and pharmaceutical and/or medicinal chemistry at universities in the United States and Canada.
Download or read book Detection Schemes Algorithms and Device Modeling for Tunable Diode Laser Absorption Spectroscopy written by Andreas Hangauer and published by . This book was released on 2013 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Develop a Diode Laser Spectroscopy System for Continuous Monitoring of Certain Gases in the Expire Air and Blood with a High Degree of Accuracy written by and published by . This book was released on 1995 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: Development of a monitor prototype to accurately measure medical gases such as O2 and CO2 content in the expired air is the objective of this program. By using the frequency modulation spectroscopy technique, we have fabricated a diode laser based sensor prototype for measuring O2 content in different concentration gas mixtures and the expired air. The prototype provides the good detection accuracy and signal-to-noise ratio. For an application purpose of breath-by-breath oxygen content monitoring, the death volume of the gas cell in the current sensor is still big and the related sample replacement time is still relatively long. The single board lock-in amplifier has to be improved. Further modifications on the lock-in amplifier and the gas cell are underway.
