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LED-Absorption-QEPAS Sensor for Biogas Plants.

Köhring M, Böttger S, Willer U, Schade W - Sensors (Basel) (2015)

Bottom Line: LEDs in the mid infrared spectral region are implemented as low cost light source.The sensor system contains an electronics unit and the two gas sensors; it was designed to work as standalone device and was tested in a biogas plant for several weeks.Gas concentration dependent measurements show a precision better than 1% in a range between 40% and 60% target gas concentration for both sensors.

View Article: PubMed Central - PubMed

Affiliation: Fraunhofer Heinrich Hertz Institute. michael.koehring@hhi.fraunhofer.de.

ABSTRACT
A new sensor for methane and carbon dioxide concentration measurements in biogas plants is presented. LEDs in the mid infrared spectral region are implemented as low cost light source. The combination of quartz-enhanced photoacoustic spectroscopy with an absorption path leads to a sensor setup suitable for the harsh application environment. The sensor system contains an electronics unit and the two gas sensors; it was designed to work as standalone device and was tested in a biogas plant for several weeks. Gas concentration dependent measurements show a precision better than 1% in a range between 40% and 60% target gas concentration for both sensors. Concentration dependent measurements with different background gases show a considerable decrease in cross sensitivity against the major components of biogas in direct comparison to common absorption based sensors.

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Concentration deviation in % of the target gas concentration for the QEPAS sensor with humidified CO2 (1) and dry N2 (2) and for the conventional sensor with humidified CO2 (3) and dry N2 (4) in comparison to the dry CO2 background gas measurements.
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sensors-15-12092-f008: Concentration deviation in % of the target gas concentration for the QEPAS sensor with humidified CO2 (1) and dry N2 (2) and for the conventional sensor with humidified CO2 (3) and dry N2 (4) in comparison to the dry CO2 background gas measurements.

Mentions: To compare the cross sensitivities of both sensors, the variation of the sensor’s response for different background gases at constant target gas concentration was derived. Dry CO2 was chosen as reference background gas for both sensors. The sensor signals were numerically fitted with an exponential function. The inverse functions of these approximations serve as calibration functions and provide the measured target gas concentrations for any given sensor signal. In a second step, the data from the measurements with humidified CO2 and dry N2 as background gases were converted into their corresponding concentrations using these calibration functions. Figure 8 shows the differences between these values and those of the dry CO2-background measurement. It can be seen that both sensors show only small cross sensitivity to water vapor. The difference between the data for dry and wet background gas at 100% target gas concentration is an artifact that shows up, as the humidified gas mixture contains a considerable amount of water vapor, even at a nominal concentration of 100% target gas. Stronger variations occur for both sensors with N2 as background gas. However, the derived concentrations show a significantly reduced cross sensitivity of about 2% for the QEPAS sensor in comparison to the conventional sensor showing about 5%.


LED-Absorption-QEPAS Sensor for Biogas Plants.

Köhring M, Böttger S, Willer U, Schade W - Sensors (Basel) (2015)

Concentration deviation in % of the target gas concentration for the QEPAS sensor with humidified CO2 (1) and dry N2 (2) and for the conventional sensor with humidified CO2 (3) and dry N2 (4) in comparison to the dry CO2 background gas measurements.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4481913&req=5

sensors-15-12092-f008: Concentration deviation in % of the target gas concentration for the QEPAS sensor with humidified CO2 (1) and dry N2 (2) and for the conventional sensor with humidified CO2 (3) and dry N2 (4) in comparison to the dry CO2 background gas measurements.
Mentions: To compare the cross sensitivities of both sensors, the variation of the sensor’s response for different background gases at constant target gas concentration was derived. Dry CO2 was chosen as reference background gas for both sensors. The sensor signals were numerically fitted with an exponential function. The inverse functions of these approximations serve as calibration functions and provide the measured target gas concentrations for any given sensor signal. In a second step, the data from the measurements with humidified CO2 and dry N2 as background gases were converted into their corresponding concentrations using these calibration functions. Figure 8 shows the differences between these values and those of the dry CO2-background measurement. It can be seen that both sensors show only small cross sensitivity to water vapor. The difference between the data for dry and wet background gas at 100% target gas concentration is an artifact that shows up, as the humidified gas mixture contains a considerable amount of water vapor, even at a nominal concentration of 100% target gas. Stronger variations occur for both sensors with N2 as background gas. However, the derived concentrations show a significantly reduced cross sensitivity of about 2% for the QEPAS sensor in comparison to the conventional sensor showing about 5%.

Bottom Line: LEDs in the mid infrared spectral region are implemented as low cost light source.The sensor system contains an electronics unit and the two gas sensors; it was designed to work as standalone device and was tested in a biogas plant for several weeks.Gas concentration dependent measurements show a precision better than 1% in a range between 40% and 60% target gas concentration for both sensors.

View Article: PubMed Central - PubMed

Affiliation: Fraunhofer Heinrich Hertz Institute. michael.koehring@hhi.fraunhofer.de.

ABSTRACT
A new sensor for methane and carbon dioxide concentration measurements in biogas plants is presented. LEDs in the mid infrared spectral region are implemented as low cost light source. The combination of quartz-enhanced photoacoustic spectroscopy with an absorption path leads to a sensor setup suitable for the harsh application environment. The sensor system contains an electronics unit and the two gas sensors; it was designed to work as standalone device and was tested in a biogas plant for several weeks. Gas concentration dependent measurements show a precision better than 1% in a range between 40% and 60% target gas concentration for both sensors. Concentration dependent measurements with different background gases show a considerable decrease in cross sensitivity against the major components of biogas in direct comparison to common absorption based sensors.

Show MeSH
Related in: MedlinePlus