Method and apparatus for monitoring gas concentrations

Abstract

The concentration of a gas, such as carbon dioxide, in a fluid medium, such as an aqueous beverage, is monitored by pulsatingly measuring a specific parameter of diffusion of the gas through a membrane that is in contact with the fluid medium and is permeable for the gas but impermeable for the fluid; the gas is allowed to diffuse during a period of time into a receiving space of known volume; the amount of gas that diffuses into the receiving space is determined e.g. by measuring IR-absorption, heat conductivity, volume, pressure or the like physical parameters that depend upon the amount of gas in the volume; this yields a specific diffusion parameter or flux. The gas concentration of interest is then calculated from the specific parameter and a previously determined general parameter of diffusion of the gas through the membrane. Pulsating operation, i.e. a repeating sequence of cyclic removal and measuring phases, is characterized by relatively short phases; since, at the same time, the receiving space volume is relatively small while the gas permeability of the membrane is relatively low, reliable results can be obtained in quick response to concentration changes. The method can be applied for monitoring or for controlling the gas concentration by adding sufficient gas to maintain a desired gas concentration in the fluid medium.