Patent ID: 6269692
Filing Date: 2001-08-07
Classification: G01F,Y10T

Abstract:
A mass flow measuring assembly for performing a multiplicity of measurements of mass flow of a gas entering the assembly at a flow rate less than a predetermined maximum flow rate from a gas storage container at a pressure less than one atmosphere and exiting the assembly into a vacuum chamber, each measurement performed within not more than a predetermined maximum response time, the assembly comprising:a capillary tube having opposed first and second ends and a central portion equidistant between said first and second ends, the tube having a circumferential outer surface and a generally cylindrical bore of a preselected diameter determining a preselected wall thickness, the tube second end in fluid communication with the gas storage container;a diffuser section having first and second apertures, the first aperture attached to and in fluid communication with the tube first end, and further having a conical, distally diverging passage therethrough symmetric about an axis of symmetry substantially in-line with the tube bore, said passage terminating proximally in said first aperture and distally in said second aperture, said second aperture in fluid communication with the vacuum chamber, said passage minimizing pressure drop of the gas exiting said second aperture; andfirst and second temperature-measuring elements, said elements in thermal contact with the outer surface of the capillary tube at about the central portion, said elements separated by a gap of a preselected width, said maximum flow rate being 10 sccm and said maximum response time being 4 seconds.