Abstract: A flow meter is adapted to measure the flow rate of a fluid flowing in the interior of a sensing conduit. The flow meter includes one sensor element disposed along the flow path of the fluid externally of the sensing conduit closer to one fluid flow port of the conduit, another sensor element disposed along the flow path of the fluid externally of the sensing conduit closer to the other fluid flow port of the conduit, an elongated structure disposed along the flow path of the fluid internally of the sensing conduit and away from the two sensor elements for reducing the fluid flow space in the sensing conduit, apparatus for heating the sensor elements, and apparatus for detecting a temperature differential between the sensor elements. The elongated structure has an end that engages the sensing conduit at a fluid flow port. The elongated structure may be a wire that is pre-bent or straight prior to its insertion into the sensing conduit, or may be a tube.

Abstract: Reduced attitude sensitivity is achieved in a fluid mass flow meter of the type which determines fluid flow from the temperature difference between an upstream sensor and a downstream sensor positioned along the flow path of the fluid externally of a sensing conduit for the fluid. A housing, taking particular forms, has wall structure spaced along the sensors adapted to substantially limit the ambient gaseous atmosphere along the sensors to a thin film. The housing wall structure further is spaced along portions of the sensing conduit between the sensors and the input and output ports of the conduit to substantially limit the ambient gaseous atmosphere along such portions to a thin film. In one form, such wall structure, along these portions, converges from both directions along the conduit, to provide support regions for the conduit. The sensors, specifically, are self-heating coil elements formed of temperature-sensitive resistance wire wound around the outside of the sensing conduit.

Abstract: A frusto-conical adjustable laminar flow bypass restrictor which is disposed within a conically tapering bore to form a conduit capable of maintaining laminar flow and adjustable to form annuli of varying thicknesses to allow proper sensor calibration over a wide range of flow rates.

Abstract: A pair of mass flow sensors are used to separately monitor the mass flow rates of a carrier gas and of a mixture of carrier gas and source vapor formed a mixing station. The rates are compared, for example by substracting the carrier gas flow rate from the mixture flow rate, to generate a signal representing the mass flow rate of the source vapor. Flow of the carrier gas to the mixing station is modulated in accordance with the difference between this signal and a command signal representing a predetermined flow rate. The system can be calibrated by flowing the carrier gas alone through both sensors, by passing the mixing station, and adjusting the signal for one or both sensors so that the signals from both sensors are equalized.

Abstract: A mass flow meter for measuring the flow rate of a fluid in a sensing tube over a wide ambient temperature range and with low sensitivity to attitude change. A pair of sensor temperature sensitive resistive wire coils are wound around the outer surface of the tube along the flow path of the fluid and are encased in open cell foam material. The sensor elements are heated and the rate of mass flow of the fluid is directly proportional to the temperature differential between the sensor elements. The sensor elements can be connected to a bridge circuit for detecting the temperature differential of the sensor elements. Tilting the sensor from the initial balance position results in a change in meter reading of less than 0.5%.