Patent ID: 7881886

Claim:
An arrangement for determining actual gas flow rate being delivered by a gas flow delivery system, said arrangement comprising: a valve, said valve being associated with a mass flow controller (MFC), said valve being configured for controlling the flow of gas through said gas flow delivery system; a manifold, said manifold being a storage tank for said gas, said manifold being positioned downstream from said valve; a gas conduit for delivery said gas from said manifold, a section of said gas conduit is wide to form an orifice, said orifice being positioned downstream from said manifold, said orifice having an area size smaller than said manifold; a set of pressure sensors, said set of pressure sensors being positioned upstream from said orifice and downstream from said manifold; and a storage container, said storage container forming a vacuum environment for receiving said gas, said storage container being positioned downstream from said orifice, said storage container being independent of a processing chamber of a plasma processing system, wherein said gas flows through said valve and said manifold at a pressure to create a choked flow condition in said orifice of said gas conduit as said gas is flowing through said gas conduit into said storage container.