US Patent 7174263 External volume insensitive flow verification

A flow verifier for in-situ verification of a device under test (DUT), including an inlet connectable to a DUT, an outlet connectable to a vacuum pump for drawing gas through the DUT and the flow verifier, a vessel having a predetermined volume, diffusive media connecting the inlet to the vessel, an outlet valve connecting the vessel to the outlet for controlling flow from the vessel to the outlet, at least one temperature sensor operatively connected to the vessel for providing temperature measurements from within the vessel, and a pressure transducer operatively connected to the vessel for providing pressure measurements from within the vessel.