An automatic low-level gas blender

Abstract

The design and construction of a new automated low-level gas mixing apparatus is described which is intended for use in the testing and characterisation of solid-state and other gas sensors. This apparatus will blend gases such as carbon monoxide with clean air to produce mixtures of 1 to 1000 parts per million and is based upon the volume proportioning principle, where a gas sample is prepared by mixing a pre-determined volume of pure gas with a known volume of clean air. The instrument is capable of producing repeatable gas mixtures at a series of specified concentrations with accuracies better than ±0.5% for the low range (1-100 ppm) and ±0.2% for the high range (100-1000ppm) as compared with concentrations measured using two calibrated commercial monitors.