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Low-power Portable Laser SpectroscopicSensors for Atmospheric CO2 Monitoring                Clinton J. Smith            Ad...
Requirements for Trace Gas Sensor NetworksA trace gas sensor for networks          Sensors work autonomouslymust provide: ...
Wireless Sensor Network & Deployment350 m range directionalantennas are used  Test Sight: Crop field in Princeton, NJ     ...
Determine detection methodDirect absorbance• current scan across absorption feature, relate I/Io to conc.           (+) ab...
Slide compliments of Mark A. Zondlo                Wavelength modulation spectroscopy• high sensitivity detection (absorba...
Slide compliments of Mark A. Zondlo              Wavelength modulation spectroscopy• add sinusoidal variation to current s...
Slide compliments of Mark A. Zondlo             Wavelength modulation spectroscopy• Fourier transform photosignal to obtai...
resulting signal has 2nd derivative shape  Slide compliments of Mark A. Zondlo
CO2 Sensor Design & Specifications•Tunable diode laser absorption spectroscopy(TDLAS)•Housed within a NEMA enclosure foren...
Custom Control and Acquisition Board                                            Direct Digital Synthesizer                ...
2 μm VCSEL & CO2 Absorption Spectrum       •Low power VCSEL                           4987 cm-1              •Consumes ~5 ...
TDLAS CO2 Sensor 3rd Harmonic Line Locking             •Control laser temperature so that 3rd             harmonic signal ...
In-Lab Tests: TDLAS CO2 Sensor Measurement                   of Changing CO2 Concentrations•   TDLAS sensor measurements w...
In-Lab Tests: TDLAS CO2 Sensor Measurement             of California Isopod Respiration•A test tube is used to hold 10 Cal...
Field Tests: TDLAS CO2 Sensor Measurement of                  Forest Floor Respiration•Soil respiration measurements were ...
Multi-Node Long-Term Cross-Correlation Performance                         Base                        Station            ...
Slide compliments of Mark A. Zondlo
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Slide compliments of Mark A. Zondlo
CO2 Sensor Allan Deviation – What’s the bigproblem?                                              29
Examples of environmental influence on data                                              30
Let’s audit the composition of CO2 sensor     24 cmLeft: CO2 sensor as seen from top.      The total size is less than tha...
Use a temperature controlled environment to            find source of driftTemperature Controlled VesselBoth sensor board ...
Allan variances from different environments…                                                                          All ...
Opto-electronics system perturbations                                        34
How to fix?•Control the laser environment•Correct for drift influence?                                 35
AcknowledgementsThis work was sponsored in part by:Nanotechnology for Clean Energy IGERTThe National Science Foundation’s ...
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Low-power Portable Laser Spectroscopic Sensors for Atmospheric CO2 Monitoring

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Low-power Portable Laser Spectroscopic Sensors for Atmospheric CO2 Monitoring

  1. 1. Low-power Portable Laser SpectroscopicSensors for Atmospheric CO2 Monitoring Clinton J. Smith Advisor: Gerard Wysocki PECS Student Dinner Talk 10/23/2011
  2. 2. Requirements for Trace Gas Sensor NetworksA trace gas sensor for networks Sensors work autonomouslymust provide: in the field Base Station•Small size/portability•Low unit/capital cost•Low maintenance and operatingcosts•Robust construction•Low power consumption•High sensitivity (ppb) Radio•High selectivity to trace gas species Range•Wireless networking capability•Ease of mass production Sensors 2
  3. 3. Wireless Sensor Network & Deployment350 m range directionalantennas are used Test Sight: Crop field in Princeton, NJ Three locations selected to monitor coupled local environments: 1. Adjacent to the local road: car traffic 2. In the inner courtyard: local vegetation 3. On the roof of the building CO2 sensor-node. The total size is less than that of a shoebox. 3
  4. 4. Determine detection methodDirect absorbance• current scan across absorption feature, relate I/Io to conc. (+) absolute measurement, straightforward (-) less sensitive, difficult to determine baselinePhotoacoustic• high power laser modulated as it is tuned across absorption line; sound waves generatedwith an amplitude proportional to concentration (+) zero baseline, high precision measurements (-) closed cell, not proportional to pathlength, long-term reproducibilityCavity ringdown• light enters high-finesse cavity, observe light decay with time (+) extremely high sensitivity (long pathlengths) (-) closed-path cell, high reflectivity mirrorsWavelength modulation spectroscopy• current scan modulated at high frequency to reduce 1/f noise (+) high sensitivity, zero baseline method (-) requires calibration, more complex electronics circumstances/conditions determine method! Slide compliments of Mark A. Zondlo
  5. 5. Slide compliments of Mark A. Zondlo Wavelength modulation spectroscopy• high sensitivity detection (absorbance 10-6 to 10-5); needs calibration - limited by optical interference fringes (étalons), not shot noise• scan current over absorption feature at 1 kHz
  6. 6. Slide compliments of Mark A. Zondlo Wavelength modulation spectroscopy• add sinusoidal variation to current scan at 250 kHz
  7. 7. Slide compliments of Mark A. Zondlo Wavelength modulation spectroscopy• Fourier transform photosignal to obtain 3rd component (2f spectra)• low noise limit (1 x 10-5 min. absorbance for 1 Hz)
  8. 8. resulting signal has 2nd derivative shape Slide compliments of Mark A. Zondlo
  9. 9. CO2 Sensor Design & Specifications•Tunable diode laser absorption spectroscopy(TDLAS)•Housed within a NEMA enclosure forenvironmental protection •Desiccant used to prevent condensation•3.5 m path Herriott multi-pass cell•2 μm VCSEL & InGaAs photodetector•Custom electronics board (openPHOTONSplatform*)•Powered by an integrated 10 Ah Li-ion polymer Laser CO2 Detectorbattery •Works for 10 hours with pump/100+ hours without pump •300 mW power consumption without pump Controlling Electronics* www.openphotons.org 9
  10. 10. Custom Control and Acquisition Board Direct Digital Synthesizer TEC driver MCU 8MHz Modulated Current Lock-In Amplifier + Front End Driver www.openphotons.orgSo, S., Sani, A. A., Zhong, L., Tittel, F., and Wysocki, G. 2009. Demo abstract: Laser-based trace-gas chemical sensors for distributed wirelesssensor networks. In /Proceedings of the 2009 international Conference on information Processing in Sensor Networks/ (April 13 - 16, 2009).Information Processing In Sensor Networks. IEEE Computer Society, Washington, DC, 427-428 10
  11. 11. 2 μm VCSEL & CO2 Absorption Spectrum •Low power VCSEL 4987 cm-1 •Consumes ~5 mW power •VCSEL temperature tuning P=1 atm range of ~5 cm-1 •Absorption coefficients in this range correspond to ~1% absorption over 3.5 m path •Choose 4987 cm-1 absorption line for line- locking •Best SNR within the VCSEL drive current and temperature Water absorption lines have limited •Low interference from H2O impact on CO2 absorption lines linesSource: HITRAN 2000 database 11
  12. 12. TDLAS CO2 Sensor 3rd Harmonic Line Locking •Control laser temperature so that 3rd harmonic signal is near zero •This corresponds to the maximum of the 2nd harmonic signal Measure the CO2 concentration by continuously monitoring the 2nd harmonic signal value at the peak 12
  13. 13. In-Lab Tests: TDLAS CO2 Sensor Measurement of Changing CO2 Concentrations• TDLAS sensor measurements were compared with measurements of a commercial sensor • Testing at 0 C shows similar behavior between TDLAS and commercial sensors • TDLAS & commercial sensor: R2 = 0.9964 • Commercial sensors compared to each other: R2 = 0.9606 - 0.9956• Soil respiration over time • Soil CO2 respiration at room temperature was measured to have a typical concentration increase slope of 0.24 ppm/sec 13
  14. 14. In-Lab Tests: TDLAS CO2 Sensor Measurement of California Isopod Respiration•A test tube is used to hold 10 California isopods in a closed path system withthe TDLAS CO2 sensor in-line•CO2 out-gassing is observed in control sample •Likely from desiccant •Repeatable out-gassing rate•Isopod signal compared against CO2 out-gassing background shows increasein CO2 concentration •Isopods detectable after ~2 minutes •Approximately 0.021 ppm/sec CO2 concentration increase 14
  15. 15. Field Tests: TDLAS CO2 Sensor Measurement of Forest Floor Respiration•Soil respiration measurements were performed at the Smithsonian EnvironmentalResearch Center •Repeated thermal cycling introduced beam walking error •TDLAS and commercial sensor produced nearly identical measurements in the control area with random foliage makeup •In an area with just Tulip Poplar leaves, TDLAS and commercial sensor measured soil CO2 respiration slopes of 0.18 ppm/sec. and 0.19 ppm/sec, respectively •Random foliage area R2 = 0.8930; Tulip Poplar leaves area R2 =0.9516 15
  16. 16. Multi-Node Long-Term Cross-Correlation Performance Base Station Node Node Node 1 2 3
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  29. 29. CO2 Sensor Allan Deviation – What’s the bigproblem? 29
  30. 30. Examples of environmental influence on data 30
  31. 31. Let’s audit the composition of CO2 sensor 24 cmLeft: CO2 sensor as seen from top. The total size is less than that of a shoebox.Right: Schematic of optical configuration and electricalcontrol systems. 31
  32. 32. Use a temperature controlled environment to find source of driftTemperature Controlled VesselBoth sensor board and optical The sensor board is placed outsidesystem are placed in the while the optical system is placedtemperature controlled inside the temperature controlledenvironment. environment. 32
  33. 33. Allan variances from different environments… All Inside, Line- LockingAll Outside, Gimbal ~0.64 ppm 1x10-5 UMDL Cell Inside, Constant ~0.29 ppm TemperatureAll Outside, Fixed Cell Inside, 2x Over-Modulation All Outside, 2x Over-Modulation 1.5x10-6 UMDL Cell Inside, Line- Locking 33
  34. 34. Opto-electronics system perturbations 34
  35. 35. How to fix?•Control the laser environment•Correct for drift influence? 35
  36. 36. AcknowledgementsThis work was sponsored in part by:Nanotechnology for Clean Energy IGERTThe National Science Foundation’s MIRTHE Engineering Research CenterAn NSF MRI award #0723190 for the openPHOTONS systemsAn innovation award from The Keller Center for Innovation in EngineeringEducation 36

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