Movatterモバイル変換

[0]ホーム
URL:

Next Article in Journal
Underdetermined DOA Estimation Using MVDR-Weighted LASSO
Previous Article in Journal
Zwitterionic Surfactant Modified Acetylene Black Paste Electrode for Highly Facile and Sensitive Determination of Tetrabromobisphenol A
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Section
Special Issue
Volume
Issue
Number
Page
 
Logical OperatorOperator
Search Text
Search Type
 
add_circle_outline
remove_circle_outline
 
 
Journals
Sensors
Volume 16
Issue 9
10.3390/s16091551
first_page
Download PDF
settings
Order Article Reprints
Font Type:
ArialGeorgiaVerdana
Font Size:
AaAaAa
Line Spacing:
Column Width:
Background:
Article

A Portable Laser Photoacoustic Methane Sensor Based on FPGA

1
School of Information Engineering, Robot Technology Used for Special Environment Key Laboratory of Sichuan Province, Southwest University of Science and Technology, Mianyang 621010, China
2
Joint Laboratory for Extreme Conditions Matter Properties, Southwest University of Science and Technology and Research Center of Laser Fusion CAEP, Mianyang 621010, China
*
Author to whom correspondence should be addressed.
Sensors2016,16(9), 1551;https://doi.org/10.3390/s16091551
Submission received: 28 July 2016 /Revised: 5 September 2016 /Accepted: 15 September 2016 /Published: 21 September 2016
(This article belongs to the SectionPhysical Sensors)

Abstract

:
A portable laser photoacoustic sensor for methane (CH4) detection based on a field-programmable gate array (FPGA) is reported. A tunable distributed feedback (DFB) diode laser in the 1654 nm wavelength range is used as an excitation source. The photoacoustic signal processing was implemented by a FPGA device. A small resonant photoacoustic cell is designed. The minimum detection limit (1σ) of 10 ppm for methane is demonstrated.

    1. Introduction

    Methane (CH4) detection plays an important role in various applications, such as natural gas exploration, coal mining, medical diagnostics and environment monitoring [1,2,3,4,5]. There exist numerous CH4 sensing devices based on different detection principles like catalytic combustion, gas chromatography (GC), electrochemical sensors, semiconductor, infrared spectroscopy, etc. [6,7,8]. Compared with the above sensors, the main advantages of laser photoacoustic (PA) gas sensors are the high sensitivity, large dynamic range, without the need for sample preparation and in situ measurement option.
    PA detection of trace gases is one of the most sensitive techniques of infrared absorption spectroscopy [9,10,11,12]. The success of PA gas detection crucially depends on the availability and performance of excitation light sources in combination with appropriate detection schemes. There are several factors affecting PA gas detection technology. The two main factors are the light source and the weak signal detection technique. Tunable near-infrared diode lasers and tunable mid-infrared quantum cascade lasers (QCLs) are generally employed as excitation light sources today [13,14,15]. The tunable distributed feedback (DFB) diode laser is the appropriate laser source for portable gas sensors due to its compact shape and stability characteristics [16,17,18,19,20]. The weak signal detection technique for the PA gas detection is another key factor. The use of a commercial lock-in amplifier makes the PA gas detection system achieve high sensitivity. These gas detection systems based on a commercial lock-in amplifier (SR830, Stanford Research Systems, Sunnyvale, CA, USA) are hardly integrated and miniaturized for their relatively large volume. With rapid development of the field-programmable gate arrays (FPGA) technology, the FPGA has extended the application of digital signal processing to a larger field of instrumentation in recent years [21,22,23,24]. The FPGA technology makes the sensors portable, reconfigurable and reprogrammable with the advantages of good low-cost, high integration and high-performance signal processing [25,26,27,28]. The digital lock-in amplifier based FPGA may provide new opportunities for developing portable PA gas detection devices.
    In this paper, a portable PA methane sensor based on FPGA in combination with a tunable distributed feedback (DFB) diode laser is developed. The performance of the sensor is demonstrated by the measurements of CH4. A detection limit of 10 ppm is obtained.

    2. Sensor Design

    A schematic of the portable PA methane sensor is shown inFigure 1. A tunable DFB, fiber-coupled diode laser (NLK1U5EAAA, central wavelength 1653.72 ± 0.05 nm, 10 mW, FC/PC pigtailed, NEL, Kanagawa-ken, Japan) is used as the excitation light source. The laser beam is collimated using a fiber optical collimator (operating wavelength 1650 nm, Primanex, Shenzhen, China) for direct installation in the resonant PA cell. The DFB diode laser is operated in wavelength modulation mode by the laser controller. Modulation of the laser current is performed by applying a sinusoidal dither to the direct current ramp of the DFB diode laser at half of the PA cell’s resonance frequency. The PA signals are detected by a 22 mV/Pa microphone (EK3033, Knowles Electronics, Chicago, IL, USA) which is placed in the middle of the PA cell resonator. The amplified PA signals by a high input impedance preamplifier (AD8221, Analog Devices, Norwood, MA, USA) are measured using the lock-in amplifier based on FPGA with a time constant 1 s. Gas concentration is displayed on a digital display after data acquisition and processing. A photograph of the portable PA sensor is shown inFigure 2 (220 × 200 × 80).
    In order to achieve a portable gas sensor, a small resonant PA cell is designed. The shape and size of this PA cell are shown inFigure 3a. The diameter and length of the brass resonator are respectively 4 mm and 36 mm. The length of two buffer volumes is 18 mm, and their diameters are 20 mm. The length of both ends flanges is 2 mm. The end of the PA cell is sealed by a quartz window. The PA cell is highly insulated with special material to reduce the environmental temperature and humidity interferences (seeFigure 3b). A temperature controller accurately controls the temperature of PA cell to maintain a temperature of 35 °C. Under this condition the PA cell’s resonance is obtained (seeFigure 4). The frequency, half-width and Q-factor of the resonance have been determined by extracting parameters from a Lorentzian fit. For this cell, the resonant frequency is 2450 Hz and the Q-factor is about 26 at atmospheric pressure.
    The lock-in amplifier based on FPGA can be seen inFigure 5. It is implemented in a ProASIC3 series low cost, low power FPGA (ProASIC3EL, ACTEL, New York, NY, USA). The FPGA is configured on a NIOS II processor (It is the second generation embedded processor architecture for FPGAs.) with C programming language. Implementing components in FPGA allows all operations after analog-to-digital (AD) sampling to be done digitally at high speed. The workflow and each functional modules of the FPGA are coordinated by this NIOS II processor [29,30]. Gas concentration is achieved to implement a computation repeatedly, composed of a series of ordered operations on a set of PA signal data. Concentrations can be directly routed to a digital-to-analog converter (DAC) as well as displayed.
    It is assumed that the PA signal isX1 =Vscos(ωt +θ), one reference signal isR1 =Vrcos(ωt +ϕ), another orthogonal reference signal isR2 =Vrsin(ωt +ϕ). When the PA signalX1 is separately multiplied by the reference signalsR1 andR2, the results are low pass filtered yielding:
    I=kVsVrcos θ
    Q=kVsVrsin θ
    According to Equations (1) and (2), the phase difference and the amplitude can now be calculated by this NIOS II processor:
    Vs=1kVrI2+Q2, θ=arctan(QI)
    whereVS is the amplitude the PA signal,θ is the phase difference of the PA signal.
    The gas sample preparation unit consists of two mass flow controllers (MFC) and two bottles of certified gas (5000 ppm CH4 and air). The two MFCs were used to dilute the certified CH4 gas. From 100 ppm to 5000 ppm, different concentrations of CH4 were generated by the sample gas preparation unit. For reducing excessive flow noise resulting from turbulence in the PA cell, a total flow of 100 standard cubic centimetres per minute (sccm) was used.

    3. Results and Discussion

    Carbon dioxide (CO2) and water vapour (H2O) are the most ubiquitous gases in the environment, which have characteristic infrared absorptions. Therefore the spectral overlap interference of none-measured gases in CH4 detection needs to be solved. An absorption line at 1653.7 nm is selected for CH4 detection by analyzing spectral range of center wavelength and light source characterictics (seeFigure 6). The absorption spectrum of H2O, CH4 and CO2 between 1620–1680 nm was obtained from the HITRAN database [31].Figure 6 shows there is no spectral overlap interference at 1653.7 nm.
    The DFB diode laser was operated under control of the operating system. The spectrum at 1653.7 nm was obtained by varying the laser operating temperature from 10 to 40 °C. The sensor was used to measure the CH4.The measured 1f spectra of 200 ppm CH4 is shown inFigure 7.
    To test the sensor performance, different concentrations ranging from 100 ppm to 2000 ppm were prepared by diluting certified methane with the gas sample preparation unit. The PA signal amplitude of different concentrations was measured as seen inFigure 8. Each dot is an average of 10 individual measurements. A linear fit was applied to obtain the linearity of the sensor. Experiments show that the PA sensor has good performance.
    The detection limit and response time of this PA methane sensor were evaluated by detecting the PA signal with diluting calibrated mixture of 5000 ppm CH4 in air. Both targeted and detected CH4 concentrations were demonstrated as shown inFigure 9. The standard deviation (σ) of the PA signal is 0.52. The PA signal amplitude of 223 ppm is 11.9 mV, so a SNR of 23 was calculated, which indicated that the detection limit (SNR = 1) of this PA sensor for CH4 is about 10 ppm. The response time is about 4 s. There are some differences between the targeted gas and measured CH4 concentrations. One of the main reasons is most likely the precision of the gas sample preparation unit during the dilution process.
    The PA signals of 2000 ppm CH4 were measured for evaluating measurement stability of this PA sensor (seeFigure 10). The CH4 concentrations were displayed in digital display, for which these values were recorded at intervals of 30 s. Its relative error is less than 0.5%. The measurement results thus show that this sensor has good stability.

    4. Conclusions

    A new gas sensor was developed, which uses a DFB diode laser, FPGA lock-in, and resonant photoacoustic spectroscopy. The proposed PA methane sensor is portable, compact, easy operation and intuitive display. A minimum detection limit of 10 ppm for CH4 was demonstrated at atmospheric pressure. Further improvements are carried out for improving the detection sensitivity by optimizing the design for the FPGA lock-in. This sensor shows the possibility of providing a new instrument for coalmine methane detection, environmental monitoring and industrial applications in combination with appropriate detection schemes.

    Acknowledgments

    This work was supported by a grant from the Natural Science Foundation of Southwest University of Science and Technology (No. 12zx7126) and the Natural Science Fund of Education Department of Sichuan province (No. 16zd1124).

    Author Contributions

    Jianwei Wang, Huili Wang and Xianyong Liu conceived and designed the experiments; Huili Wang performed the experiments; Jianwei Wang and Huili Wang analyzed the data; Jianwei Wang contributed the idea; Jianwei Wang and Huili Wang contributed the experimental results and all of figures in measurements; Jianwei Wang wrote the paper.

    Conflicts of Interest

    The authors declare no conflict of interest.

    References

    1. Li, J.; Lu, X.T.; Yang, Z.H. Remote system of natural gas leakage based on multi-wavelength characteristics spectrum analysis.Spectrosc. Spect. Anal.2014,34, 1249–1252. [Google Scholar]
    2. Jahjah, M.; Ren, W.; Stefanski, P.; Lewicki, R.; Zhang, J.W.; Jiang, W.Z.; Tarka, J.; Tittel, F.K. A compact QCL based methane and nitrous oxide sensor for environmental and medical applications.Analyst2014,139, 2065–2069. [Google Scholar] [CrossRef] [PubMed]
    3. Karacan, C.Ö.; Ruiz, F.A.; Cotè, M.; Phipps, S. Coal mine methane: A review of capture and utilization practices with benefits to mining safety and to greenhouse gas reduction.Int. J. Coal Geol.2011,86, 121–156. [Google Scholar] [CrossRef]
    4. Cheng, Y.-P.; Wang, L.; Zhang, X.-L. Environmental impact of coal mine methane emissions and responding strategies in China.Int. J. Greenh. Gas. Control2011,5, 157–166. [Google Scholar] [CrossRef]
    5. Costello, B.P.J.D.; Ledochowski, M.; Ratcliffe, N.M. The importance of methane breath testing: A review.J. Breath Res.2013,7, 024001. [Google Scholar] [CrossRef] [PubMed]
    6. Shemshad, J.; Aminossadati, S.M.; Kizil, M.S. A review of developments in near infrared methane detection based on tunable diode laser.Sens. Actuators B Chem.2012,171, 77–92. [Google Scholar] [CrossRef]
    7. Wang, C.J.; Sahay, P. Breath analysis using laser spectroscopic techniques: Breath biomarkers, spectral fingerprints, and detection limits.Sensors2009,9, 8230–8262. [Google Scholar] [CrossRef] [PubMed]
    8. Sigrist, M.W.; Bartlome, R.; Marinov, D.; Rey, J.M.; Vogler, D.E.; Wachter, H. Trace gas monitoring with infrared laser-based detection schemes.Appl. Phys. B2008,90, 289–300. [Google Scholar] [CrossRef]
    9. Wang, J.; Zhang, W.; Liang, L.; Yu, Q. Tunable fiber laser based photoacoustic spectrometer for multi-gas analysis.Sens. Actuators B Chem.2011,160, 1268–1272. [Google Scholar] [CrossRef]
    10. Jahjah, M.; Jiang, W.Z.; Sanchez, N.P.; Ren, W.; Patimisco, P.; Spagnolo, V.; Herndon, S.C.; Griffin, R.J.; Tittel, F.K. Atmospheric CH4 and N2O measurements near greater Houston area landfills using a QCL-based qepas sensor system during discover-AQ 2013.Opt. Lett.2014,39, 957–960. [Google Scholar] [CrossRef] [PubMed]
    11. Patel, C.K.N. Laser photoacoustic spectroscopy helps fight terrorism: High sensitivity detection of chemical warfare agent and explosives.Eur. Phys. J. Spec. Top.2008,153, 1–18. [Google Scholar] [CrossRef]
    12. Rocha, M.V.; Sthel, M.S.; Silva, M.G.; Paiva, L.B.; Pinheiro, F.W.; Miklos, A.; Vargas, H. Quantum-cascade laser photoacoustic detection of methane emitted from natural gas powered engines.Appl. Phys. B2012,106, 701–706. [Google Scholar] [CrossRef]
    13. Holthoff, E.L.; Heaps, D.A.; Pellegrino, P.M. Development of a mems-scale photoacoustic chemical sensor using a quantum cascade laser.IEEE Sens. J.2010,10, 572–577. [Google Scholar] [CrossRef]
    14. Sampaolo, A.; Patimisco, P.; Giglio, M.; Vitiello, M.; Beere, H.; Ritchie, D.; Scamarcio, G.; Tittel, F.; Spagnolo, V. Improved tuning fork for terahertz quartz-enhanced photoacoustic spectroscopy.Sensors2016,16, 439. [Google Scholar] [CrossRef] [PubMed]
    15. Sigrist, M.W. Trace gas monitoring by laser photoacoustic spectroscopy and related techniques (plenary).Rev. Sci. Instrum.2003,74, 485–490. [Google Scholar] [CrossRef]
    16. Hanyecz, V.; Mohacsi, A.; Pogany, A.; Varga, A.; Bozoki, Z.; Kovacs, I.; Szabo, G. Multi-component photoacoustic gas analyzer for industrial applications.Vib. Spectrosc.2010,52, 63–68. [Google Scholar] [CrossRef]
    17. Besson, J.P.; Schilt, S.; Thevenaz, L. Sub-ppm multi-gas photoacoustic sensor.Spectrochim. Acta. A2006,63, 899–904. [Google Scholar] [CrossRef] [PubMed]
    18. Webber, M.E.; Pushkarsky, M.; Patel, C.K.N. Fiber-amplifier-enhanced photoacoustic spectroscopy with near-infrared tunable diode lasers.Appl. Opt.2003,42, 2119–2126. [Google Scholar] [CrossRef] [PubMed]
    19. Kosterev, A.A.; Bakhirkin, Y.A.; Tittel, F.K. Methane detection by means of quartz enhanced photoacoustic spectroscopy in NIR. In Proceedings of the 2007 Conference on Lasers & Electro-Optics/Quantum Electronics and Laser Science Conference (CLEO/QELS 2007), Baltimore, MD, USA, 6–11 May 2007. [CrossRef]
    20. Ma, Y.; Yu, G.; Zhang, J.; Yu, X.; Sun, R.; Tittel, F. Quartz enhanced photoacoustic spectroscopy based trace gas sensors using different quartz tuning forks.Sensors2015,15, 7596–7604. [Google Scholar] [CrossRef] [PubMed]
    21. Bernard-Schwarz, M.; Zwick, W.; Wenzel, L.; Klier, J.; Groschl, M. Field programmable gate array-assigned complex-valued computation and its limits.Rev. Sci. Instrum.2014,85, 093104. [Google Scholar] [CrossRef] [PubMed]
    22. Schwettmann, A.; Sedlacek, J.; Shaffer, J.P. Field-programmable gate array based locking circuit for external cavity diode laser frequency stabilization.Rev. Sci. Instrum.2011,82, 103103. [Google Scholar] [CrossRef] [PubMed]
    23. Takeda, K. A highly integrated FPGA-based nuclear magnetic resonance spectrometer.Rev. Sci. Instrum.2007,78, 033103. [Google Scholar] [CrossRef] [PubMed]
    24. Restelli, A.; Abbiati, R.; Geraci, A. Digital field programmable gate array-based lock-in amplifier for high-performance photon counting applications.Rev. Sci. Instrum.2005,76, 093112. [Google Scholar] [CrossRef]
    25. Jinghong, L.; Kai, L.; Peng, Y. Design and Implementation of Flame Combustion State Detection System Based on FPGA. In Proceedings of the 2015 27th Chinese Control and Decision Conference, Qingdao, China, 23–25 May 2015.
    26. Botella, G.; Martín H., J.A.; Santos, M.; Meyer-Baese, U. FPGA-based multimodal embedded sensor system integrating low- and mid-level vision.Sensors2011,11, 8164–8179. [Google Scholar] [CrossRef] [PubMed]
    27. González, D.; Botella, G.; Meyer-Baese, U.; García, C.; Sanz, C.; Prieto-Matías, M.; Tirado, F. A low cost matching motion estimation sensor based on the NIOS II microprocessor.Sensors2012,12, 13126–13149. [Google Scholar] [CrossRef] [PubMed] [Green Version]
    28. Rodriguezdonate, C.; Botella, G.; Garcia, C.; Cabalyepez, E.; Prietomatias, M. Early experiences with opencl on FPGAs: Convolution case study. In Proceedings of the IEEE International Symposium on Field-Programmable Custom Computing Machines, Vancouver, BC, Canada, 3–5 May 2015; p. 235.
    29. González, D.; Botella, G.; García, C.; Prieto, M.; Tirado, F. Acceleration of block-matching algorithms using a custom instruction-based paradigm on a NIOS II microprocessor.EURASIP J. Adv. Signal. Process.2013,2013, 1–20. [Google Scholar] [CrossRef]
    30. Windh, S.; Ma, X.; Halstead, R.J.; Budhkar, P.; Luna, Z.; Hussaini, O.; Najjar, W.A. High-level language tools for reconfigurable computing.Proc. IEEE2015,103, 390–408. [Google Scholar] [CrossRef]
    31. Rothman, L.S.; Gordon, I.E.; Barbe, A.; Benner, D.C.; Bernath, P.E.; Birk, M.; Boudon, V.; Brown, L.R.; Campargue, A.; Champion, J.P.; et al. The HITRAN 2008 molecular spectroscopic database.J. Quant. Spectrosc. Radiat. Transfer2009,110, 533–572. [Google Scholar] [CrossRef]
    Sensors 16 01551 g001 1024
    Figure 1. Schematic configuration of the PA methane sensor.
    Figure 1. Schematic configuration of the PA methane sensor.
    Sensors 16 01551 g001
    Sensors 16 01551 g002 1024
    Figure 2. The photograph of this PA methane sensor.
    Figure 2. The photograph of this PA methane sensor.
    Sensors 16 01551 g002
    Sensors 16 01551 g003 1024
    Figure 3. (a) The PA cell and (b) the constant temperature treatment device.
    Figure 3. (a) The PA cell and (b) the constant temperature treatment device.
    Sensors 16 01551 g003
    Sensors 16 01551 g004 1024
    Figure 4. The resonance profiles showing the first longitude resonance frequency is 2450 Hz.
    Figure 4. The resonance profiles showing the first longitude resonance frequency is 2450 Hz.
    Sensors 16 01551 g004
    Sensors 16 01551 g005 1024
    Figure 5. Schematic diagram of the FPGA based lock in amplifier.
    Figure 5. Schematic diagram of the FPGA based lock in amplifier.
    Sensors 16 01551 g005
    Sensors 16 01551 g006 1024
    Figure 6. Absorption spectrum of the gases (H2O, CO2 and CH4) obtained from the HITRAN database.
    Figure 6. Absorption spectrum of the gases (H2O, CO2 and CH4) obtained from the HITRAN database.
    Sensors 16 01551 g006
    Sensors 16 01551 g007 1024
    Figure 7. Measured 1f spectra of 200 ppm CH4.
    Figure 7. Measured 1f spectra of 200 ppm CH4.
    Sensors 16 01551 g007
    Sensors 16 01551 g008 1024
    Figure 8. PA signals to different concentrations. Error bars give the range of the corresponding PA signals.
    Figure 8. PA signals to different concentrations. Error bars give the range of the corresponding PA signals.
    Sensors 16 01551 g008
    Sensors 16 01551 g009 1024
    Figure 9. Measured dilution process of the 5000 ppm CH4 reference concentration.
    Figure 9. Measured dilution process of the 5000 ppm CH4 reference concentration.
    Sensors 16 01551 g009
    Sensors 16 01551 g010 1024
    Figure 10. Continuous measurements of 2000 ppm CH4.
    Figure 10. Continuous measurements of 2000 ppm CH4.
    Sensors 16 01551 g010

    © 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).

    Share and Cite

    MDPI and ACS Style

    Wang, J.; Wang, H.; Liu, X. A Portable Laser Photoacoustic Methane Sensor Based on FPGA.Sensors2016,16, 1551. https://doi.org/10.3390/s16091551

    AMA Style

    Wang J, Wang H, Liu X. A Portable Laser Photoacoustic Methane Sensor Based on FPGA.Sensors. 2016; 16(9):1551. https://doi.org/10.3390/s16091551

    Chicago/Turabian Style

    Wang, Jianwei, Huili Wang, and Xianyong Liu. 2016. "A Portable Laser Photoacoustic Methane Sensor Based on FPGA"Sensors 16, no. 9: 1551. https://doi.org/10.3390/s16091551

    APA Style

    Wang, J., Wang, H., & Liu, X. (2016). A Portable Laser Photoacoustic Methane Sensor Based on FPGA.Sensors,16(9), 1551. https://doi.org/10.3390/s16091551

    Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further detailshere.

    Article Metrics

    No
    No

    Article Access Statistics

    For more information on the journal statistics, clickhere.
    Multiple requests from the same IP address are counted as one view.
    Sensors, EISSN 1424-8220, Published by MDPI
    RSSContent Alert

    Further Information

    Article Processing Charges Pay an Invoice Open Access Policy Contact MDPI Jobs at MDPI

    Guidelines

    For Authors For Reviewers For Editors For Librarians For Publishers For Societies For Conference Organizers

    MDPI Initiatives

    Sciforum MDPI Books Preprints.org Scilit SciProfiles Encyclopedia JAMS Proceedings Series

    Follow MDPI

    LinkedIn Facebook X
    MDPI

    Subscribe to receive issue release notifications and newsletters from MDPI journals

    © 1996-2025 MDPI (Basel, Switzerland) unless otherwise stated
    Terms and Conditions Privacy Policy
    We use cookies on our website to ensure you get the best experience.
    Read more about our cookieshere.
    Accept
    Back to TopTop
    [8]ページ先頭
    ©2009-2025 Movatter.jp