Abstract: A reference volume for use with pressure change flow rate measurement apparatus has an internal structure comprising elements with cross section and length comparable to the cross section and length of adjacent interstitial fluid regions. The reference volume may have one or more heat conduction elements exterior to and in good thermal contact with a corrosion resistant material that defines the internal fluid holding region.

Abstract: A system comprises a flow restrictor connected to a fluid flow path and located upstream from a chamber. The flow restrictor comprises an adjustable flow restriction aperture defined by the flow path region between a first element and a second element of the flow restrictor, and a drive unit configured to adjust the relative positions of the first element, second element or both to modify the fluid flow path across the aperture. The first or second element provides a curved boundary in the aperture flow path to form a converging region, a region of closest approach and a diverging region, within the flow path. Flow rate may be determined using a reference volume upstream from the flow restrictor.

Abstract: A self-correcting pressure-based mass flow control apparatus includes outlet pressure sensing to enable correction for non-ideal operating conditions. Further the mass flow control apparatus having a fluid pathway, a shutoff valve in the fluid pathway, a reference volume in the fluid pathway, a first pressure measuring sensor in fluid communication with the reference volume, a first temperature measuring sensor providing a temperature signal indicative of the fluid temperature within the reference volume, a proportional valve in the fluid pathway, and a second pressure measuring sensor in fluid communication with the fluid pathway.

Abstract: A reference volume for use with pressure change flow rate measurement apparatus has an internal structure comprising elements with cross section and length comparable to the cross section and length of adjacent interstitial fluid regions. The reference volume may have one or more heat conduction elements exterior to and in good thermal contact with a corrosion resistant material that defines the internal fluid holding region.