초록 ▼

A thermal mass flow meter for measuring flow rate of a fluid includes a conduit that is configured to receive the fluid and that defines a primary flow path between an inlet and an outlet of the conduit. The conduit is bound at least in part by a sensor receiving surface. A thermal sensor tube has

A thermal mass flow meter for measuring flow rate of a fluid includes a conduit that is configured to receive the fluid and that defines a primary flow path between an inlet and an outlet of the conduit. The conduit is bound at least in part by a sensor receiving surface. A thermal sensor tube has a thermal sensing portion that is mounted relative to the sensor receiving surface in a direction substantially perpendicular to both the primary flow path and the sensor receiving surface. When the thermal mass flow meter is mounted in a vertical direction so that fluid within the conduit flows in the vertical direction along the primary flow path, fluid within the sensor tube flows in a horizontal direction so as to substantially prevent thermal siphoning when the sensor tube is heated.

대표청구항 ▼

What is claimed is: 1. A thermal mass flow meter for measuring flow rate of a fluid, the thermal mass flow meter comprising: a conduit configured to receive the fluid and defining a primary flow path between an inlet and an outlet of the conduit, the conduit bounded at least in part by a sensor rec

What is claimed is: 1. A thermal mass flow meter for measuring flow rate of a fluid, the thermal mass flow meter comprising: a conduit configured to receive the fluid and defining a primary flow path between an inlet and an outlet of the conduit, the conduit bounded at least in part by a sensor receiving surface; and a thermal sensor tube having a thermal sensing portion mounted relative to the sensor receiving surface in a direction that is substantially perpendicular to both the primary flow path and the sensor receiving surface; wherein when the thermal mass flow meter is mounted in a vertical direction so that fluid within the conduit flows in the vertical direction along the primary flow path, fluid within the thermal sensing portion of the sensor tube flows in a horizontal direction so as to substantially prevent thermal siphoning when the sensor tube is heated. 2. The thermal mass flow meter of claim 1, further comprising a bypass within the conduit, the bypass configured to restrict a flow of fluid entering the inlet of the conduit so as divert a portion of the fluid onto an input end of the sensor tube. 3. The thermal mass flow meter of claim 2, wherein the bypass comprises a pressure dropping bypass configured to generate a pressure differential across the sensor tube. 4. The thermal mass flow meter of claim 1, wherein pressure at the inlet of the conduit is between about 4 Torr to about 1200 Torr. 5. The thermal mass flow meter of claim 2, further comprising a supporting element configured to support the sensor tube in the direction substantially perpendicular to the sensor receiving surface, and to secure the sensor tube onto the conduit. 6. The thermal mass flow meter of claim 5, wherein the supporting element includes one or more apertures, the apertures configured to allow the fluid to pass through the sensor tube and to re-enter the primary flow path at a location that is downstream relative to the bypass. 7. The thermal mass flow meter of claim 1, further comprising a temperature measurement system configured to measure a temperature differential between at least two locations along the thermal sensing portion of the sensor tube, when the sensor tube is heated and fluid flows within the heated sensor tube. 8. The thermal mass flow meter of claim 7, wherein the temperature measurement system comprises: a pair of thermally sensitive resistive elements, each of the elements having a resistance that varies as a function of temperature of the element; and a device configured to determine the temperature of each of the elements by measuring the resistance of each element. 9. The thermal mass flow meter of claim 1, further comprising a heater configured to heat at least a portion of the sensor tube. 10. The thermal mass flow meter of claim 9, wherein the heater comprises a pair of heating coils configured to resistively heat the thermal sensing portion of the sensor tube when an electric current is supplied thereto. 11. A thermal mass flow controller for controlling flow rate of a fluid, the thermal mass flow controller comprising: a conduit configured to receive the fluid and defining a primary flow path between an inlet and an outlet of the conduit, the conduit bounded at least in part by a sensor receiving surface; a thermal sensor tube having a thermal sensing portion mounted relative to the sensor receiving surface in a direction substantially perpendicular to both the primary flow path and the sensor receiving surface; a temperature measuring system configured to measure a temperature differential between at least two locations along the thermal sensing portion of the sensor tube, when the sensor tube has been heated and fluid flows within the heated sensor tube; and a control valve configured to regulate flow of the fluid into the inlet and out of the outlet of the conduit, so that the fluid flows from the outlet at a desired flow rate; wherein when the thermal mass flow meter is mounted in a substantially vertical direction so that fluid within the conduit flows in the vertical direction along the primary flow path, fluid within the thermal sensing portion of the sensor tube flows in a horizontal direction so as to substantially prevent thermal siphoning when the sensor tube is heated. 12. The mass flow controller of claim 11, further comprising a bypass within the conduit, the bypass configured to restrict a flow of a fluid entering the inlet of the conduit so as divert a portion of the fluid onto an input end of the sensor tube. 13. The mass flow controller of claim 12, wherein the bypass comprises a pressure dropping bypass configured to generate a pressure differential across the sensor tube. 14. The mass flow controller of claim 13, wherein pressure at the inlet of the conduit is between about 4 Torr to about 1200 Torr. 15. The mass flow controller of claim 11, wherein a width of the mass flow controller is less than about 1.2 inches. 16. The mass flow controller of claim 12, further comprising a supporting element configured to support the sensor tube in the direction substantially perpendicular to the sensor receiving surface and to the primary flow path. 17. The mass flow controller of claim 16, wherein the supporting element includes one or more apertures, the apertures configured to allow the fluid to pass through the sensor tube and to re-enter the primary flow path at a location that is downstream relative to the bypass. 18. A method of preventing thermal siphoning in a mass flow controller for controlling flow rate of a fluid, the mass flow controller including a thermal sensor tube having a thermal sensing portion, the mass flow controller further including a conduit configured to receive the fluid, the conduit defining a primary flow path between an inlet and an outlet of the conduit and bounded at least in part by a sensor receiving surface, the method comprising: mounting the thermal sensing portion of the thermal sensor tube relative to the sensor receiving surface in a direction that is substantially perpendicular to both the primary flow path and the sensor receiving surface; wherein when the mass flow controller is mounted in a vertical direction so as to cause fluid within the conduit to flow along the primary flow path in the vertical direction, fluid within the thermal sensing portion of the sensor tube flows along a horizontal direction so as to substantially prevent thermal siphoning when the sensor tube is heated. 19. The method of claim 18, further comprising supporting the sensor tube in the substantially perpendicular direction with a supporting element.