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- Gaynullin, Bakhram, 1967-, et al.
(författare)
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Advanced Pressure Compensation in High Accuracy NDIR Sensors for Environmental Studies
- 2023
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Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 23:5
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of atmospheric gas concentrations using of NDIR gas sensors requires compensation of ambient pressure variations to achieve reliable result. The extensively used general correction method is based on collecting data for varying pressures for a single reference concentration. This one-dimensional compensation approach is valid for measurements carried out in gas concentrations close to reference concentration but will introduce significant errors for concentrations further away from the calibration point. For applications, requiring high accuracy, collecting, and storing calibration data at several reference concentrations can reduce the error. However, this method will cause higher demands on memory capacity and computational power, which is problematic for cost sensitive applications. We present here an advanced, but practical, algorithm for compensation of environmental pressure variations for relatively low-cost/high resolution NDIR systems. The algorithm consists of a two-dimensional compensation procedure, which widens the valid pressure and concentrations range but with a minimal need to store calibration data, compared to the general one-dimensional compensation method based on a single reference concentration. The implementation of the presented two-dimensional algorithm was verified at two independent concentrations. The results show a reduction in the compensation error from 5.1% and 7.3%, for the one-dimensional method, to −0.02% and 0.83% for the two-dimensional algorithm. In addition, the presented two-dimensional algorithm only requires calibration in four reference gases and the storing of four sets of polynomial coefficients used for calculations.
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| 4. |
- Gaynullin, Bakhram, 1967-, et al.
(författare)
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Environmental monitoring of methane utilizing multispectral NDIR gas sensing for compensation of spectral impact from water vapor in air
- 2022
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Ingår i: Proceedings of IEEE Sensors. - : IEEE. - 9781665484640
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 5. |
- Gaynullin, Bakhram, 1967-
(författare)
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High accuracy low-cost NDIR sensing
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sensing gas concentrations using optical absorption offers valuable advantages over other methods ina wide variety of real-world applications from industrial processes to environmental change. One of the most rapidly developing detection techniques on the global market is the non-dispersive infrared method (NDIR). Sensors developed based on this technique satisfy a growing demand for low-cost, reliable and long-term maintenance-free solutions. The technologies available to support this field for sensor key components such as light sources, photo detectors, optic cavities, and electronic components, have advanced rapidly in recent years. This development has led to an increasing number of application fields, due to significant improvements in accuracy, sensitivity and resolution.However, this technique has limitations related to basic physical principles and sensor design performance. Variation in sensing environments’ temperature and pressure, the impact of water vapour presence and sensor component ageing are the most important interfering factors for investigation. Errors in measured values could be caused by any of these factors because they influence various sensor parts and the environment’s physical properties. The correct interpretation of error sources is one the most difficult and important tasks involved in designing stable, high-precision sensors.To facilitate investigations into measurement performance limitations, test equipment was developed along with test approaches capable of creating experimental conditions that exceed the tested sensor’ stolerances. The studied resolution limit for long-path sensors is about 100 ppb. For measurements in fresh air concentrations (approximately 400 ppm of CO2), this is equivalent to a precision of less than0.1%. The methods used to reduce possible inaccuracies due to various error sources’ impacts should possess compensatory capabilities and precisions that exceed this value.To improve the pressure compensation procedure’s performance, a complete advanced system that includes everything from a lab test bench to the supporting software and comprehensive calculation algorithm was developed. The test bench creates pressure conditions that deviate from the reference value by less than 0.2 mbar (or 0.02% of the standard pressure, 1013 mbar).One of this study’s major findings is the concentration range-independent pressure compensation method. The advanced conditions achieved with the test station also facilitated the discovery and characterisation of the sources of long-term drift in methane concentration measurement.
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| 7. |
- Gaynullin, Bakhram, 1967-, et al.
(författare)
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Implementation of NDIR technology for selective sensing of gases with common absorption spectra
- 2023
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Ingår i: 2023 IEEE International Instrumentation and Measurement Technology Conference (I2MTC). - : IEEE. - 9781665453837
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Konferensbidrag (refereegranskat)abstract
- 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.
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