Abstract
A Non-Dispersive Infra-Red (NDIR) gas analyzer has been designed, and a proof-of concept built and validated, to continuously monitor water vapor and carbon dioxide gas partial pressures, for a space-based instrument application, that requires the safe transfer of sublimated volatiles from a comet sample containment system to a gas containment system within the operational pressure-temperature conditions, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</i> .g., water vapor, in the range 3 Torr (268 K) and 30 mTorr (223 K). The NDIR gas analyzer uses quad thermopile detectors integrated with spectral bandpass comprising filters centered at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.7 ~ \mu \text{m}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6.58 ~ \mu \text{m}$ </tex-math></inline-formula> for water absorption channels, spectral bandpass filter centered at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.25 ~ \mu \text{m}$ </tex-math></inline-formula> for carbon dioxide absorption channel, and spectral band-pass filter centered at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.0 ~ \mu \text{m}$ </tex-math></inline-formula> for the reference channel, paired with a pulsed infra-red source. The thermopile detector signals are measured and processed using a custom-built radiation-hard-by-design multi-channel digitizer (MCD) application specific integrated circuit (ASIC). The NDIR gas analyzer can detect water vapor partial pressures up to 3 Torr with a 30 mTorr resolution (1 sigma) and carbon dioxide partial pressures up to 175 Torr with a 50 mTorr resolution (1 sigma) within the temperature range 223–268 K.
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