Patent ID: 8141433

Claim:
A method of measuring the gas flow of an incondensable gas in a flowing mixture of said incondensable gas and a condensable gas comprising the steps of: a) calibrating a leak detector at a given temperature and pressure with a calibration mixture supplied at a given flow rate, said calibration mixture comprising a gauge gas of known absolute concentration and said incondensable gas, the concentration of said gauge gas in the calibration mixture being measured by the leak detector; b) injecting a known quantity of gauge gas at a known mass flow rate into said flowing mixture of gases at an inlet point which is sufficiently spaced from a sample point which is downstream of the inlet point so as to ensure that, at said sample point, there is a uniform gauge mix of said gauge gas and said mixture of gases; c) drawing a sample of the said gauge mix off at said sample point, d) passing said sample through a condenser so as to remove said condensable gas from the gauge mix, resulting in a test mix; e) passing the said test mix into the leak detector at said given temperature, pressure and flow rate, the leak detector measuring the concentration of said gauge gas within the test mix; f) calculating the mass flow rate of said incondensable gas within said flowing mixture as a function of concentration of gauge gas in the calibration mixture, concentration of the gauge gas in the test mix, mass flow rate of the injected gauge gas and the absolute concentration of the gauge gas within the calibration mixture.