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

Abhishek Upadhyay, Michael Lengden, David Wilson, Gordon Samuel Humphries, Andrew P. Crayford, Daniel G. Pugh, Mark P. Johnson, George Stewart, Walter Johnstone

Research output: Contribution to journalArticle

6 Citations (Scopus)
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Abstract

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 CO2 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.
Original languageEnglish
Article number6804611
Number of pages12
JournalIEEE Photonics Journal
Volume10
Issue number6
Early online date27 Nov 2018
DOIs
Publication statusE-pub ahead of print - 27 Nov 2018

Keywords

  • wavelength modulation spectroscopy
  • Calibration-free TDLS
  • 1f-WMS

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