초록 ▼

A flow rate sensor includes a main conduit, a sensor tube and a bypass tube connecting an upstream portion of the main conduit to a downstream portion of the main conduit such that flow through the main conduit is divided through the sensor tube and the bypass tube, and at least one heater element f

A flow rate sensor includes a main conduit, a sensor tube and a bypass tube connecting an upstream portion of the main conduit to a downstream portion of the main conduit such that flow through the main conduit is divided through the sensor tube and the bypass tube, and at least one heater element for heating the sensor tube. A first flow restrictor of porous media is positioned between the upstream portion of the main conduit and the sensor tube, and a second flow restrictor of porous media is positioned between the upstream portion of the main conduit and the bypass tube. The flow restrictors provide the flow rate sensor with a fixed bypass ratio so that the sensor can operate independently of the type of gas being measured.

대표청구항 ▼

What is claimed is: 1. A flow rate sensor, comprising: a main conduit including an upstream portion, a downstream portion, and an intermediate portion disposed between and in series with the upstream and downstream portions, wherein the intermediate portion includes a sensor tube and a bypass tube

What is claimed is: 1. A flow rate sensor, comprising: a main conduit including an upstream portion, a downstream portion, and an intermediate portion disposed between and in series with the upstream and downstream portions, wherein the intermediate portion includes a sensor tube and a bypass tube disposed and oriented so as to be parallel to one another such that flow through the main conduit is divided between the sensor tube and the bypass tube; at least one heater element for heating the sensor tube; a first porous media flow restrictor positioned between the upstream portion of the main conduit and the sensor tube; and a second porous media flow restrictor positioned between the upstream portion of the main conduit and the bypass tube. 2. A sensor according to claim 1, wherein the porous media comprises sintered metal. 3. A sensor according to claim 2, wherein the sintered metal is formed from metal powder having a pre-sintered mean particle size is less than 20 microns. 4. A sensor according to claim 3, wherein the the pre-sintered mean particle size is less than 10 microns. 5. A sensor according to claim 2, wherein the sintered metal has a density of at least 5 g/cc. 6. A sensor according to claim 2, wherein the sintered metal is selected from the group consisting of stainless steel, nickel and nickel alloys, and titanium. 7. A sensor according to claim 1, wherein the heather element comprises an upstream resistance coil and a downstream resistance coil. 8. A sensor according to claim 1, wherein the coils are connected to a Wheatstone bridge. 9. A mass flow controller including a flow rates sensor according to claim 1, and further including: a valve for controlling mass flow through the main conduit of the flow rate sensor; and a processor connected to the flow rate sensor and the valve and programmed to receive a desired flow rate, compare the desired flow rate to an actual flow rate as measured using the flow rate sensor, and, if the actual flow rate does not equal the desired flow rate, operate the valve until the actual flow rate equals the desired flow rate. 10. A sensor according to claim 1, wherein the first and the second porous media flow restrictors have permeabilities that are substantially the same. 11. A sensor according to claim 1, wherein the first and the second porous media flow restrictors have thicknesses that are substantially the same. 12. A sensor according to claim 1, wherein the first and the second porous media flow restrictors have cross-sectional flow areas that are substantially the same. 13. A sensor according to claim 1, wherein the first and second flow restrictors each include a central plane that are located substantially within the same plane. 14. A sensor according to claim 13, wherein the first and second flow restrictors include first and second disks, respectively, wherein the firstand second disks are disposed in first and second openings, respectively, of a metal plate positioned between (i) the upstream portion of the main conduit and (ii) the intermediate portion, and wherein the first flow restrictor connects the upstream portion of the main conduit to to the sensor tube and the second flow restrictor connects the upstream portion of the main conduit to the bypass tube. 15. A method of measuring a fluid flow rate, comprising: providing a main conduit having an upstream portion, a downstream portion, and an intermediate portion connected between and in series with the upstream and downstream portions, wherein the intermediate portion includes a sensor tube and a bypass tube configured and oriented so as to be parallel to one another; dividing a fluid flow through the main conduit into the sensor tube and the bypass tube; heating the sensor tube; restricting flow in the sensor tube using a first porous media flow restrictor; and restricting flow in the main conduit and the bypass tube using a second porous media flow restrictor. 16. A method according to claim 15, wherein the porous media comprises sintered metal. 17. A method according to claim 16, wherein the sintered metal is formed from metal powder having a pre-sintered mean particle size of less than 20 microns. 18. A method according to claim 17, wherein the mean particle size of the sintered elements is less than 10 microns. 19. A method according to claim 16, wherein the sintered metal has a density of at least 5 g/cc. 20. A method according to claim 16, wherein the sintered metal is selected from the group consisting of stainless steel, nickel and nickel alloys, and titanium. 21. A method according to claim 15, wherein the sensor tube is heated using an upstream resistance coil and a downstream resistance coil. 22. A method according to claim 21, wherein the coils are connected to a Wheatstone bridge. 23. A method according to claim 15, wherein the first and second flow restrictors each include a central plane further including locating the central planes of the first and second flow restrictors within substantially the same plane. 24. A method according to claim 23, wherein the first and second flow restrictors includes first and second disks, respectively, and wherein locating the central planes of the first and second flow restrictors within the same plane includes disposing the first and second disks in first and second openings, respectively, of a metal plate positioned between (i) the upstream portion of the main conduit and (ii) the intermediate portion, such that the first flow restrictor connects the upstream portion of the main conduit to the sensor tube and the second flow restrictor connects the upstream portion of the main conduit to the bypass rube. 25. A method for controlling a mass flow of a fluid, comprising: providing a main conduit for receiving the flow of fluid, the main conduit including an upstream portion, a downstream portion, and an intermediate portion connected between and in series with the upstream and downstream portions, wherein the intermediate portion includes a sensor tube and a bypass tube configured and oriented so as to parallel to one another; dividing a fluid flow main conduit into the sensor tube and the bypass tube; restricting flow between the upstream portion of the main conduit and the sensor tube using a first flow restrictor comprising a porous media; restricting flow between the upstream portion of the main conduit and the bypass tube using a second flow restrictor comprising a porous media; receiving a desired total rate of mass flow in the main conduit at a location upstream of the upstream portion; measuring a rate of mass flow through the sensor tube and the bypass tube using known reference gas flow versus voltage calibration data; comparing the desired total rate of mass flow to the actual total rate of mass flow; and adjusting the rate of fluid flow through the main conduit until the actual rate of mass flow equals the desired rate of mass flow. 26. A method according to claim 25, wherein the first and second flow restrictors each include a central plane, further including locating the central planes of the first and second flow restrictors within substantially the same plane. 27. A method according to claim 26, wherein the first and second flow restrictors includes first and second disks, respectively, and wherein locating the central planes of the first and second flow restrictors within the same plane includes disposing the first and second disks in first and second openings, respectively, of a metal plate positioned between (i) the upstream portion of the main conduit and (ii) the intermediate portion, such that the first flow restrictor connects the upstream portion of the main conduit to the sensor tube and the second flow restrictor connects the upstream portion of the main conduit to the bypass tube.