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A new RAM normalized 1f-WMS technique for the measurement of gas parameters in harsh environments and a comparison with 2f/1f

Upadhyay, Abhishek, Lengden, Michael, Wilson, David, Humphries, Gordon Samuel, Crayford, Andrew P. ORCID:, Pugh, Daniel G. ORCID:, Johnson, Mark P., Stewart, George and Johnstone, Walter 2018. A new RAM normalized 1f-WMS technique for the measurement of gas parameters in harsh environments and a comparison with 2f/1f. IEEE Photonics Journal 10 (6) , 6804611. 10.1109/JPHOT.2018.2883548

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A calibration-free 1f wavelength modulation spectroscopy (1f-WMS) technique for gas species parameter measurement is demonstrated. In this technique, the total magnitude of the first harmonic (1f) WMS signal is normalised by a component of the 1f residual amplitude modulation (1f-RAM) signal. This method preserves the advantages of traditional nf/1f-WMS (n×2) technique, such as immunity to the non-absorbing systematic losses and accurate recovery of gas parameters without the requirement for non-absorbing regions for normalisation at high pressure or high modulation index values (m-values). The proposed technique only requires the first harmonic signal, which has the largest magnitude of all the harmonics signals, and therefore fundamentally has a higher sensitivity to the nf/1f technique. Furthermore, since only the 1f-WMS signal is used the technique is less complex in terms of signal processing and data acquisition. The paper also shows a comparison of the proposed technique and 2f/1f for measuring CO $_{2}$ in the exhaust of a combuster. This data highlights how nonlinearities in the optical detection system as a function of frequency have a considerable effect on the recovered 2f/1f spectra causing variation in the recovered gas concentrations. This effect is not seen in the methodology proposed in this paper.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Engineering
Additional Information: This article is licensed under a Creative Commons Attribution 4.0 International License.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
ISSN: 1943-0655
Date of First Compliant Deposit: 29 November 2018
Date of Acceptance: 21 November 2018
Last Modified: 04 May 2023 23:22

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