Abstract: A baffle is positioned near a diaphragm of a capacitive pressure sensor to have a small volume therebetween. The baffle creates a high aspect ratio path to create molecular flow for molecules to travel before reaching the diaphragm. The path encourages contaminants to stick to the baffle or housing before reaching the diaphragm. The sensor further includes a particle trap between an inlet and the baffle.

Abstract: A vapor delivery system for delivering a vapor-phase reactant to a chemical process reactor at a substantially constant flow rate. The vapor delivery system includes a source of a reactant material, means for converting the reactant material to a vapor and for maintaining a predetermined volume of vapor in a vapor phase, a flow controller for providing a controlled flow of the vapor-phase reactant to the process reactor, means for detecting a parameter related to the availability of the vapor-phase reactant material to the process reactor from the flow controller, and means responsive to the detection signal for controlling the supply of reactant material to the vapor converter. In one embodiment the parameter is the pressure of the vapor within the predetermined volume. In another embodiment the parameter is the fluid conductance of a control valve within the flow controller. The vapor delivery system of the present invention can operate in either a substantially continuous or a noncontinuous delivery mode.

Abstract: Apparatus for and method of measuring mass flow of a gas in a gas delivery system. The apparatus is adapted to be connected to a source of a gas. The apparatus includes a fixed-volume chamber in fluid connection with the gas source. A flow control device can be used to control the flow of the gas into the chamber. A transducer assembly comprises, in combination, a pressure transducer in fluid connection with the chamber, and a signal modifying network associated with the pressure transducer. The pressure transducer permits measurement of the pressure of the gas in the chamber and provides a first electrical signal representative of the pressure of the known volume of the gas. The signal modifying network modifies the first signal to produce an output signal which is proportional to PV/RT and thus directly represents the number of moles of the gas in the chamber. The apparatus is useful for calibrating mass flow controllers and the like.

Abstract: A pressure measurement and calibration apparatus for accurately detecting fluid pressures in the range of between approximately 0 and 1000 millitorr, and more particularly in the range of between 0 and 10 millitorr, and a method for calibrating an external pressure measuring device using the apparatus. The apparatus employs a pressure sensing assembly having a deflectable diaphragm and sensing electrodes. The assembly is rotated about an axis which is normal to the direction of local gravitational acceleration through preselected angles relative to the direction of local gravitational acceleration. The apparatus generates an output signal representative of the deflection of the diaphragm due to gravitational acceleration on the diaphragm at a given angular orientation. The apparatus then controllably conducts a fluid flow against the diaphragm at a sufficient pressure to substantially eliminate the deflection attributable to gravity on the diaphragm.

Abstract: The disclosed mass flow transducer is of the type including a balanced bridge comprising two, substantially identical, thermal elements forming two sides of the bridge between the top and the bottom of the bridge, the two elements being adapted to be positioned in two regions of a laminar flow tube in a symmetrical tandem arrangement so as to sense flow through the tube, one element being upstream from the other. The preferred transducer includes control means for monitoring the voltage at the top and bottom of the bridge and monitoring the current required to maintain the node between the thermal elements at virtual ground.

Abstract: A constant temperature gradient fluid mass flow transducer is described. The upstream and downstream ends of a measuring section of a capillary tube of the transducer are held at respective constant temperatures by separate temperature regulated heat sinks, the downstream end being hotter. A heat conducting outer tube surrounds the measuring section and joins the heat sinks to cause the measuring section temperature to assume a substantially linear profile at a constant gradient. An electrical heater supplies heat uniformly to the measuring section to replace that transferred to the flowing fluid within the capillary tube and thereby keep the temperature and gradient constant. The voltage across the heater, proportional to the square root of mass flow rate, is taken as the output signal.