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An FPGA-based lock-in detection system to enable chemical species tomography using TDLAS

Chighine, Andrea and Fisher, Edward and Wilson, David and Lengden, Michael and Johnstone, Walter and McCann, Hugh (2015) An FPGA-based lock-in detection system to enable chemical species tomography using TDLAS. In: 2015 IEEE International Conference on Imaging Systems and Techniques (IST). IEEE, Piscataway, NJ, pp. 1-5. ISBN 9781479986330

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Abstract

This paper presents the design, implementation and test of a compact, low-cost and fully digital signal recovery system for tunable diode laser absorption spectroscopy (TDLAS) in narrow line-width gas sensing applications. An FPGA-based digital lock-in amplifier (DLIA), in conjunction with TDLAS using the wavelength modulation spectroscopy (WMS) technique, is utilized to demodulate and extract first (1f) and second (2f) harmonic signals for a narrow CO2 feature in the spectrum region of 1997.2nm. The spectrum in this wavelength region shows suitably weak water absorption, enabling CO2 detection with high resolution. Gas-cell experiments were carried out using the DLIA and a conventional rack-mounted commercial lock-in amplifier. The comparison between the two systems shows good agreement, validating the feasibility of this approach and demonstrating the prospect for extension to a massively multichannel system to implement Chemical Species Tomography.