METHOD OF, AND APPARATUS FOR, PROVIDING A GAS MIXTURE

摘要

There is provided a gas mixer arrangement comprising a first gas source for supplying a first gas; a second gas source for supplying a second gas different from said first gas; a first valve for regulating the flow of the first gas; a second valve for regulating the flow of the second gas; a mixer located downstream of the first and second valves and arranged, in use, to mix the first and second gases to provide a mixed gas; a meter arranged to measure the average molecular weight of the mixed gas, comprising a high-frequency planar piezoelectric crystal oscillator in contact with the mixed gas and a sensor operable to determine atmospheric pressure; and a controller operable, in response to the measured average molecular weight of said mixed gas, to control at least one of said first and second valves in order to control the relative proportion of the first and second gases in said mixed gas.

主权项

1. A method of providing a mixture of gases in a relative proportion, the mixture comprising at least a first gas and a second gas different from the first gas, the method comprising:
a) supplying the first gas from a first gas source at a first flow rate; b) supplying the second gas from a second gas source at a second flow rate; c) mixing the first and second gases to form a mixed gas; and d) supplying the mixed gas to an outlet at approximately atmospheric pressure, wherein the method further comprises: e) measuring a resonant frequency of a high-frequency planar piezoelectric crystal oscillator in contact with the mixed gas; f) measuring atmospheric pressure; g) determining the density of the mixed gas from said measured resonant frequency; h) determining, from the density, atmospheric pressure measurement and determined or pre-determined temperature of the gas, the average molecular weight of the mixed gas; and i) automatically controlling, in response to said determined average molecular weight, one of the first and second flow rates to control the relative proportion of the first and second gases in said mixed gas.