Method and apparatus for monitoring the content of binary gas mixtures

Abstract

A method and apparatus for continuously monitoring the ratio of gases in a two gas mixture such as a therapeutic oxygen/nitrogen mixture. The gas mixture is passed through a sample tube within which ultrasound waves travel in successive bursts of pulses at the resonant frequency of the transmitter/receiver pair. Between bursts is a quiescent time period having a duration long enough to assure dissipation of transients so that standing waves do not form. The delay caused by the transit time of the sound through the gas sample generates electrical pulses that are translated into an analog signal which is then temperature-corrected. The resulting voltage, which is proportional to the transit time and thus to the gas composition, is compared with adjustable reference voltages to trigger high and low audio/visual alarms. A digital display provides a constant readout of the percentage of the gas component having the highest molecular weight. The sample tube is contained inside a larger cylindrical body to enhance the gas flow and provide thermal insulation which allows temperature compensation to be accurately performed.