Micromachined thermal mass flow sensors and insertion type flow meters and manufacture methods
First Claim
1. An integrated mass flow rate sensor comprising:
- a set of temperature sensors connected as part of a first circuit with a heating element disposed between said temperature sensors for measuring a temperature difference between an upstream and downstream temperature sensing elements for measuring a flow rate in a first range of flow rates; and
a resistive sensing element comprising an ambient temperature sensor in series connection with a resistor Rc having a constant resistance in combination with said heating element as part of a second circuit for measuring a heat loss of said heating element with reference to an ambient temperature for measuring a flow rate in a second range of flow rates wherein said first circuit and said second circuit simultaneously apply both said temperature difference between said upstream and downstream temperature sensing elements and said heat loss of said heat element respectively for concurrently measuring said flow rate that may fall within said first range of flow rates or said second range of flow rates whereby said integrated flow rate sensor having an expanded range of flow rate measurement covering said first range and said second range.
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Accused Products
Abstract
An integrated mass flow sensor is manufactured by a process of carrying out a micro-machining process on an N or P-type silicon substrate with orientation <100>. This mass flow sensor comprises a central thin-film heater and a pair of thin-film heat sensing elements, and a thermally isolated membrane for supporting the heater and the sensors out of contact with the substrate base. The mass flow sensor is arranged for integration on a same silicon substrate to form a one-dimensional or two-dimensional array in order to expand the dynamic measurement range. For each sensor, the thermally isolated membrane is formed by a process that includes a step of first depositing dielectric thin-film layers over the substrate and then performing a backside etching process on a bulk silicon with TMAH or KOH or carrying out a dry plasma etch until the bottom dielectric thin-film layer is exposed. Before backside etching the bulk silicon, rectangular openings are formed on the dielectric thin-film layers by applying a plasma etching to separate the area of heater and sensing elements from the rest of the membrane. This mass flow sensor is operated with two sets of circuits, a first circuit for measuring a flow rate in a first range of flow rates and a second circuit for measuring a flow rate in a second range of flow rates, to significantly increase range of flow rate measurements, while maintains a high degree of measurement accuracy.
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Citations
34 Claims
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1. An integrated mass flow rate sensor comprising:
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a set of temperature sensors connected as part of a first circuit with a heating element disposed between said temperature sensors for measuring a temperature difference between an upstream and downstream temperature sensing elements for measuring a flow rate in a first range of flow rates; and a resistive sensing element comprising an ambient temperature sensor in series connection with a resistor Rc having a constant resistance in combination with said heating element as part of a second circuit for measuring a heat loss of said heating element with reference to an ambient temperature for measuring a flow rate in a second range of flow rates wherein said first circuit and said second circuit simultaneously apply both said temperature difference between said upstream and downstream temperature sensing elements and said heat loss of said heat element respectively for concurrently measuring said flow rate that may fall within said first range of flow rates or said second range of flow rates whereby said integrated flow rate sensor having an expanded range of flow rate measurement covering said first range and said second range. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. An integrated mass flow rate sensor comprising:
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a set of temperature sensors with a heating element disposed between said temperature sensors connected as part of a first signal measuring circuit for measuring a temperature difference between said temperature sensors for measuring a flow rate in a first flow range; and a resistive sensing element comprising an ambient temperature sensor in series connection with a resistor Rc having a constant resistance wherein said ambient temperature sensor and said resistor Rc connected in combination with said heating element as part of a second signal measuring circuit for measuring a mass flow rate by sensing a heat loss of said heating element wherein said first and second signal measuring circuits simultaneously measuring said temperature difference between said temperature sensors and said heat loss of said heating element respectively measure at least two different ranges of flow rate with a first range of flow velocity below a saturation flow velocity and a second range of flow velocity above said saturation flow velocity. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31)
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32. A method for measuring a mass flow rate comprising:
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measuring a flow rate in a first range of flow rates by connecting a set of temperature sensors as part of a first circuit and disposing a heating element between said set of temperature sensors for measuring a temperature difference between upstream and. downstream temperature sensing elements; and measuring a flow rate in a second range of flow rates by connecting a resistive sensing element to function as an ambient temperature sensor connected in series with a resistor Rc having a constant resistance as part of a second circuit for measuring a heat loss of said heating element with reference to an ambient temperature wherein said first circuit and said second circuit simultaneously apply both said temperature difference between said upstream and downstream temperature sensing elements and said heat loss of said heat element respectively for concurrently measuring said flow rate that may fall within said first range of flow rates or said second range of flow rates. - View Dependent Claims (33, 34)
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Specification