Method and apparatus for measuring and controlling volumetric flow rate of gases in a line

A method for delivering gas through a line to a point of use at a selected and measured volumetric flow rate comprising:

• flowing gas through a line toward said point of use;
• imposing uniformity of rate of flow on said flowing gas a selected downstream point in said line by flowing the gas through a restriction in the line and establishing and maintaining a uniform pressure in the gas introduced into said restriction;
• temporarily interrupting flow of gas in said line at a selected point in said line upstream of said selected downstream point, said temporary interruption occupying a selected time interval and being repeated at selected times;
• and
• measuring the rate of fall of pressure in the portion of said line lying between said upstream and downstream points during at least a portion of the duration of said temporary interruption to obtain a measurement of the volumetric rate of flow at ambient conditions unaffected by variability in gas composition, viscosity, or density.

Apparatus for determining the volumetric flow rate of gas flowing in a line comprising:

• means for imposing uniformity of flow rate on said gas at a downstream point in said line;
• upstream valve means for temporarily restricting gas flow in said line at a point upstream from said downstream point;
• and
• means for measuring the rate of pressure fall in said line between said upstream and downstream points during at least part of the time said gas flow is restricted by said upstream valve means, said rate of pressure fall being substantially proportional to the volumetric flow rate of the gas.