Continuous monitoring of methane emissions has assumed greater significance in the recent past due to increasing focus
on global warming issues. Many industries have also identified the need for ppm level methane measurement as a means
of gaining carbon credits. Conventional instruments based on NDIR spectroscopy are unable to offer the high selectivity
and sensitivity required for such measurements. Here we discuss the development of a robust VCSEL based system for
accurate low level measurements of methane. A possible area of application is the measurement of residual methane
whilst monitoring the output of flare stacks and exhaust gases from methane combustion engines. The system employs a
Wavelength Modulation Spectroscopy (WMS) scheme with second harmonic detection at 1651 nm. Optimum
modulation frequency and ramp rates were chosen to maintain high resolution and fast response times which are vital for
the intended application. Advanced data processing techniques were used to achieve long term sensitivity of the order of
10-5 in absorbance. The system is immune to cross interference from other gases and its inherent design features makes it
ideal for large scale commercial production. The instrument maintains its calibration and offers a completely automated
continuous monitoring solution for remote on site deployment.
A new clinical diagnostic instrument for urea breath test (UBT) based non-invasive detection of Helicobacter
Pylori is presented here. Its compact and low cost design makes it an economical and commercial alternative
for the more expensive Isotope Ratio Mass Spectrometer (IRMS). The instrument is essentially a two channel
non-dispersive IR spectrometer that performs high precision ratio measurements of the two carbon isotopomers
(12CO2 and 13CO2) present in exhaled breath. A balanced absorption system configuration was designed where
the two channel path lengths would roughly be in the ratio of their concentrations. Equilibrium between the
transmitted channel intensities was maintained by using a novel feedback servo mechanism to adjust the length
of the 13C channel cell. Extensive computational simulations were performed to study the effect of various
possible interferents and their results were considered in the design of the instrument so as to achieve the desired
measurement precision of 1%. Specially designed gas cells and a custom made gas filling rig were also developed.
A complete virtual interface for both instrument control and data acquisition was implemented in LABVIEW.
Initial tests were used to validate the theory and a basic working device was demonstrated.
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