Mid Sweden University

A system for the measurement of methane concentration in water is presented. The system is a stand- alone device using a high-resolution NDIR (Non-Dispersive Infra-Red) gas sensor. The NDIR sensor is configured to measure methane, water vapor, and carbon dioxide in the air. It is mounted in a housing with a stabilized environment and includes cross-sensitivity compensation. An equilibrator is used to transfer the methane concentration from the water into a circulating gas flow that is analyzed by the NDIR gas sensor. The equilibrator consists of a vertical plastic tube filled with 2,000 glass marbles, where the water runs from top to bottom on the surface of the glass marbles, in contact with a circulating air flow, exchanging gas. The system is stand- alone, including power supply and logging features for 72 hours of operation. The system performance was evaluated in a field test, measuring the methane content of seawater at a fiber bank in Sundsvall, Sweden. This fiber bank consists of remaining waste from an old paper industry from before 1970 and is known to produce methane. The detection limit of the tested system is below 1.4 nmol/L in water, corresponding to 1 ppm methane concentration in the air. The settling time of the system in its current configuration, including the equilibrator and gas sensor housing, is 30 minutes. 

A selective algorithm for nondispersive infrared (NDIR) sensing of gases with overlapping absorption spectra was developed and evaluated in modified multichannel NDIR sensor. Measurements in the optic channel with the spectral band where two gas species (target and secondary gas) have overlapping absorption lines are complemented by additional measurements in second channel where spectral absorption for only one gas (secondary gas) is present. The real concentration for the target gas is retrieved by adjusting the absorption data obtained in the overlapping gas spectra's optic channel, with respect to the absorption data retrieved in the second optic channel that has sensitivity only for the secondary gas. An implementation example is performed by obtaining the true concentration of CH4 (as target gas) in a mixture with H2O vapor. The channel for the target gas is equipped by an optic filter with spectra at 3.375 μm where both CH4 and H2O have absorption lines. The complementary second channel provides sensing in spectra at 2.7 μm where only H2O have absorption. Data from a third channel, at 3.95 μm, is used as reference value for 'zero-level' calibration. A calibration procedure was developed and tested, which involves matching of the absorbed light energy in target and secondary channels in humid reference environments. A selective algorithm for sensing of CH4 with elimination of spectral impact from H2O was validated in environments with variable CH4 and H2O concentrations. By implementing the multispectral approach and the developed algorithm, an uncertainties of 5-10 ppm relative the reference concentrations were achieved. For the environments where selective algorithm was validated this should be compared to an uncertainty of 70-90 ppm for the non-corrected CH4 concentration. 

A multispectral nondispersive infrared (NDIR) sensor was developed for simultaneous detection of methane and water vapor in air. The NDIR sensor is capable of measuring optic transmission in the CH4 absorption spectra at 3.375 μm and the H2O absorption spectra at 2.7 μm. Data from a third channel, 3.95 μm, is used as reference value for 'zero-level' calibration. The actual CH4 concentration is retrieved by adjusting the data obtained in the CH4 spectra with respect to the concentration sensed in the H2O spectra. A calibration procedure was developed and tested, which involves matching of the absorbed light energy in the CH4 and the H2O spectrum in humid reference environments. A compensation algorithm for elimination of humidity impact was developed and validated in environments with variable CH4 and H2O concentrations. By implementing the multispectral approach, and the developed algorithm, an uncertainty of 15-25 ppm relative the reference concentrations was achieved. For a concentration range valid for environmental monitoring applications this should be compared to an uncertainty of 180-200 ppm for the non-corrected CH4 concentration. 

Carbon dioxide (CO2) is a gas vital for life on Earth. It is also a waste product of human activities and is widely used in agriculture and industry. Its accurate sensing is therefore of great interest. Optical sensors exploiting the mid-infrared light absorption of CO2 provide high selectivity, but their large size and high cost limit their use. In this Letter, we demonstrate CO2 gas sensingat 4.2 μm wavelength using an integrated silicon waveguide, featuring a sensitivity to CO2of 44% that of free-space sensing. The suspended waveguide is fabricated on a silicon-on-insulator substrate by a single-lithography-step process, and we route it into a mid-infrared photonic circuit for on-chip-referenced gas measurements. Its demonstrated performance and its simple and scalable fabrication make our waveguide ideal for integration in miniaturized CO2 sensors for distributed environmental monitoring, personal safety, and medical and high-volume consumer applications. © 2019 Optical Society of America.

Can one technical solution help prevent drowsy drivers and detect a child left behind? Yes, using a single, maintenance-free, Non-Dispersive Infrared (NDIR) gas sensor integrated in the cabin ventilation system. Carbon dioxide (CO2) is an established proxy for ventilation needs in buildings. Recently, several studies have been published showing a moderate elevation of the indoor carbon dioxide level effect cognitive performance such as information usage, activity, focus and crisis response. A study of airplane pilots using 3-hour flight simulation tests, showed pilots made 50% more mistakes when exposed to 2,500 ppm carbon dioxide compared to 700 ppm. This has a direct impact on safety. All living animals and humans exhale carbon dioxide. In our investigations we have found that an unintentionally left behind child, or pet, can easily be detected in a parked car by analyzing the carbon dioxide trends in the cabin. Even an 8-month old baby acts as a carbon dioxide source, increasing cabin CO2 levels at a 20ppm/minute rate allowing for detection within one minute. Vehicles running with the ventilation system in recirculation mode normally reach above the fresh air limit of 1,000 ppm within a few minutes. The carbon dioxide level normally stabilizes between 3,000 and 10,000 ppm. Levels that will make the driver drowsy, reducing their cognitive performance and impact safety. Using an NDIR gas sensor in the ventilation system will reduce driver performance degradation due to elevated carbon dioxide levels, allowing reliable detection of any unintentionally left behind children or pets, potentially saving lives. © 2020 SAE International. All Rights Reserved.