Abstract: An assembly for measuring the mass flow and flow rate of gases such as are used in semiconductor fabrication processes. The assembly includes an axial flow passage, viz., a capillary tube with a bore of about 0.050 inch diameter and a wall thickness of about 0.002 inch, having a downstream end connected to a diffuser section having an axially symmetric, diverging passage. Gas exiting the diffuser section has a low pressure drop because the gas has expanded at a low, controlled rate, converting velocity head into pressure head, and because the tube and diffuser section passage are in-line, eliminating right-angle turns. The assembly also includes two resistance thermometers, coils of iron-nickel alloy wire about 0.0004 inch in diameter, providing a differential temperature measurement with a time constant of less than 4 seconds.

Abstract: A fluid valve assembly including a ball valve within a central hole in a resilient disc-shaped spring. The spring has additional openings to minimize resistance to fluid flow from inlet to outlet. Clearance between the spring and side walls of the cavity within which it is mounted allows the ball to center itself in its seat. The central hole diameter, ball diameter and separation between the spring and seat are selected to create an upward force on the ball over its entire stroke which provides a frictional force between the spring and a supporting lip to minimize radial motion of the spring to keep the ball aligned. The force also overcomes the weight of the ball in applications where the inlet pressure is very low, and also overcomes adhesion of the ball to the seat. The assembly is incorporated in a mass flow controller typically used with semiconductor fabrication processes.

Abstract: A method of correcting measurement errors of an instrument for measuring the flow of a gas, the instrument having a selected measuring range and being constructed to produce a reading indicating the value of a gas flow in the selected measuring range, by the steps of: selecting a limited number of gas flow values which are spaced apart across the measuring range; determining the readings produced by the instrument when the instrument is measuring gas flows at the selected values; measuring the flow of the gas with the instrument to produce a reading indicating the value of the gas flow; and producing a corrected reading by calculating a function of the reading produced in the measuring step and the readings produced in the determining step.

Abstract: A method and apparatus for calibrating a flow sensor composed of two heat sensors each having an electrical impedance parameter which varies as a defined function of the temperature of the heat sensor and disposed in thermal communication with a fluid such that the relation between heat flow to or from one sensor and heat flow to or from the other sensor varies with the rate of fluid flow, a source supplying electric power at a selected level to the heat sensors, and an output device connected to produce an output signal representative of that heat flow relation, calibration being performed by: establishing a known flow rate for the fluid; electrically connecting one of the heat sensors to a circuit element which alters the magnitude of current flowing through the one heat sensor; and determining, in a first determining step, output signal value while the one heat sensor is electrically connected to the circuit element.

Abstract: A disconnectable flow connector is formed of (a) a frusto-conical taper pin having a longitudinal bore through which the end portion of a flow tube of a mass flow sensor is inserted and secured and (b) a connector base containing a matched frusto-conical taper bore. The taper pin can be press-fit into the taper bore to form a fluid flow passage having a leakage level less than about 10.sup.-9 scc/sec helium. with a series of spaced apart, transverse grooves separated by lands in sealing engagement with the matched taper bore.

Abstract: A hermetically sealed, precision fluid valve assembly including a ball valve element is disclosed. The assembly includes a valve element retainer comprising a thin, flexible member having a first portion operatively associated with the valve element and a second portion, extending from the first, secured to the body of the valve assembly. The valve element retainer guides the motion of the valve element and is designed to reduce friction and eliminate the generation and entrapment of contaminants, thereby minimizing hysteresis in the operation of the valve.