Thermal mass flowmeter and controller

Claim 2

A mass flowmeter comprising: a semiconductor body; a thin film first flow sensor suspended in a flow channel in said body; a thin film stagnant flow sensor suspended in a stagnant gas channel in said body; and a body temperature sensor attached to said body for providing an indication of the temperature of inlet gas flow in said flow channel to said first flow sensor.

Claim 3

The flowmeter of Claim 1 further comprising: means, including a bridge circuit, for processing electrical signals from said sensors indicative of the temperature of said sensors; and means for deriving a gas mass flow rate signal from said bridge circuit.

Claim 4

The flowmeter of Claim 2 further comprising: means responsive to said gas mass flow rate signal for controlling gas flow from said gas flow channel.

Claim 5

The flowmeter of Claim 3 in which said means for controlling gas flow includes a control valve in flow communication with said gas flow channel and said bridge circuit includes means for supplying a bridge voltage indicative of gas thermal conductivity which bridge voltage schedules valve gain in said control valve.

Claim 6

The flowmeter of claim 4 further comprising means for outputing said bridge voltage to allow monitoring and estimation of gas species when the gas is unknown to estimate the ratio of known gases in a mixture of unknown ratios.

Claim 7

The flowmeter of Claim 1 in which said semiconductor body comprises: a first semiconductor substrate having an etched flow channel extending on a surface thereof, said first flow sensor being suspended across said etched flow channel and being integral with said substrate; a first stagnant gas channel in said first substrate and extending parallel to said etched flow channel, said stagnant gas channel being connected to said inlet gas flow and including wall means for blocking flow of inlet gas through said stagnant gas channel; and a second substrate having a gas flow channel and a stagnant gas channel spacedly extending on a surface thereof, said second substrate being mounted and sealed on said first substrate such that said gas flow channel and said stagnant gas channels are aligned to form a gas flow conduit and a stagnant gas conduit, respectively, in said body.

Claim 8

The flowmeter of claim 6 in which said first and second substrates are bonded together utilizing a chemically inert and high temperature tolerant bonding agent which has suitable thermo plastic, adhesive, and chemical inert properties.

Claim 9

The flowmeter of Claim 1 in which said first flow sensor and said stagnant flow sensor are identical such that said stagnant flow sensor provides a reference signal equivalent to the first flow sensor but at zero gas flow.

Claim 10

The flowmeter of Claim 1 in which said body temperature sensor is attached to a surface of said body near said flow channel and said stagnant gas channel.

Claim 11

The flowmeter of Claim 1 further including means for heating said first flow sensor and said stagnant flow sensor.

Claim 12

The flowmeter of Claim 10 in which said means for heating comprises electrical power means connected to a resistance film pattern on said first flow sensor and a resistance film pattern on said stagnant flow sensor.

Claim 13

The flowmeter of Claim 11 further comprising: means for regulating said stagnant flow sensor temperature rise to a constant temperature rise above the temperature of the body temperature sensor.

Claim 14

The flowmeter of Claim 12 further comprising: means for processing electrical signals from said first flow sensor and stagnant flow sensor indicative of the temperature of said first flow sensor and stagnant flow sensor.

Claim 15

The flowmeter of Claim 12 further comprising: means for processing electrical signals from said first flow sensor and stagnant flow sensor indicative of the temperature of said first flow sensor and stagnant flow sensor; means for supplying heating current to said first flow sensor and said stagnant flow sensor to keep the first flow sensor temperature equal to the stagnant flow sensor temperature; and means for measuring the current needed to equalize said temperatures, as an indicator of mass flow rate.

Claim 16

The flowmeter of Claim 14 further comprising: . means for processing electrical signals from said first flow sensor and stagnant flow sensor indicative of the temperature of said first flow . sensor and stagnant flow sensor; means for supplying heating current to said first flow sensor and said stagnant flow sensor to keep the first flow sensor voltage equal to the stagnant flow sensor voltage; and means for measuring the current needed to equalize said voltages, as an indicator of mass flow rate.

Claim 17

The flowmeter of Claim 1 in which the sensors are selected from the class consisting of resistors, semiconducting diodes or transistors operated as self heated temperature sensors.

Claim 18

The flowmeter of Claim 1 in which said sensors are resistors having a measurable temperature coefficient of resistance.

Claim 19

The flowmeter of Claim 1 in which said sensors are self-heating semiconductor devices and include means for exciting the sensors by forward biasing a junction with current sufficient so as to be self-heated.

Claim 20

The flowmeter of Claim 1 further including a proportioning control valve coupled to said flow sensor channel; and a feedback control circuit for regulating gas flow.

Claim 21

The flowmeter of Claim 1 in which each of said sensors are thin-film resistors.

Claim 22

The flowmeter of Claim 1 in which said body temperature sensor comprises thin film resistors extending on a surface of said body adjacent an edge of said stagnant gas channel.

Claim 23

The flowmeter of Claim 1 in which said semiconductor body is a silicon wafer and includes a multiplicity of stagnant gas channels and stagnant flow sensors, a multiplicity of gas flow channels and first flow sensors and a multiplicity of body temperature sensors adjacent to peripheral edges of said wafer, said channels and sensors being oriented such that multiple gas mass flow signals may be averaged to control inlet gas flow.

Claim 24

The flowmeter of Claim 22 in which gas flow channels in said body are axially aligned such that inlet gas flows first past an unused first flow sensor in one of said flow channels, the inlet gas then flows past an operative first flow sensor in a continuation of said one channel after developing a laminar flow condition.

Claim 25

The flowmeter of Claim 1 further comprising: means for processing electrical signals from said sensors indicative of the temperature of said sensors; means for deriving a gas mass flow rate signal from said sensor electrical signals; and controller means responsive to said gas means flow rate signal for controlling gas flow from said gas flow channel.

Claim 26

The flowmeter of Claim 24 wherein said controller means includes an in-line control valve in flow communication with said gas flow channel.

Claim 27

The flowmeter of Claim 25 wherein said control valve is down stream of said gas flow channel; said control valve including a housing, a flow orifice in said housing, an armature containing a valve seal in said housing and an armature electromagnetic coil actuatable by said flow rate signal for moving said valve seal with respect to said orifice to control the flow of gas through said orifice and said flow channel.

Claim 28

The flowmeter of Claim 1 having a passivation film coating all surfaces of the sensors and sensor flow channels to reduce chemical reactions.

Claim 29

The flowmeter of Claim 1 in which said body includes a cover substrate of high thermal conductivity material to provide a uniform ambient wall temperature insensitive to externally generated thermal gradients.

Claim 30

The flowmeter of Claim 1 having sufficiently small channel geometries such as to inhibit internal gas convection and_to provide a flowmeter insensitive positionally with respect to gravity.

Claim 31

The flowmeter in Claim 1 in which said body includes a cover of high thermal conductivity material to provide a uniform channel wall temperature to maintain a flowing gas at an ambient temperature equal to the wall temperature.

Claim 32

The flowmeter of Claim 1 in which said body temperature sensor is a thin film gas temperature sensor suspended in the flow channel near a flow channel inlet, for indicating a temperature of the incoming gas.

Claim 33

The flowmeter of Claim 1 further including a sensor and by-pass module, said module comprising passive by-pass flow channels and active flow channels, said by-pass flow channels having a similar pressure drop as a function of flow to the active flow channels and means for varying the number of by-pass channels to provide the number required for additional flow capacity above the flow capacity of the active flow channels.

Claim 34

In combination, a gas means flow controller comprising: a housing having a gas inlet port, a gas outlet port and a central bore; a valve seat sealingly fixed in said housing bore and having a flow passage in flow communication with said housing outlet port at one end and having a flow orifice at an opposed end; a translatable armature spring-mounted in said housing bore, said armature having a valve seal mounted at one end and a through flow passage, said armature and valve seal being movable with respect to said valve seat orifice to control gas flow through said orifice; a pole piece having a flow passage in communication with said armature flow passage and mounted in said housing bore, said pole piece being spaced from an end of said spring-mounted armature opposite said fixed valve seal; a sensor and by-pass module sealingly mounted in said housing in flow communication with said pole piece flow passage and said gas inlet port; said module comprising a passive gas-flow segment and an active gas-flow segment, said active gas flow segment including a semiconductor body, a thin film flow sensor suspended in a flow channel in said body, a thin film stagnant flow sensor suspended in a stagnant gas channel in said body and a body temperature sensor attached to said body adjacent to said channels for providing an indication of the temperature of inlet gas flow in said gas channel to said flow sensor; a closure plug for closing said housing top incorporating sensor signal feed-through pins, and coil means surrounding said armature , and being actuatable in response to electrical signals from said sensors to move said armature.

Claim 35

In combination, a gas means flow controller comprising: a housing having a gas inlet port, a gas outlet port and a central bore; a valve seat sealingly fixed in said housing bore and having a flow passage in flow communication with said housing outlet port at one end and having a flow orifice at an opposed end; a translatable armature spring-mounted in said housing bore, said armature having a valve seal mounted at one end and a through flow passage, said armature and valve seal being movable with respect to said valve seat orifice to control gas flow through said orifice; a pole piece having a flow passage in communication with said armature flow passage and mounted in said housing bore, said pole piece being spaced from an end of said spring-mounted armature opposite said fixed valve seal; a sensor and by-pass module sealingly mounted in said housing in flow communication with said pole piece flow passage and said gas inlet port; said module comprising a passive gas-flow segment and an active gas-flow segment, said active gas flow segment including a semiconductor body, a thin film flow sensor suspended in a flow channel in said body, a thin film stagnant flow sensor suspended in a stagnant gas channel in said body and a body temperature sensor attached to said body adjacent to said channels for providing an indication of the temperature of inlet gas flow in said gas channel to said flow sensor; a closure plug for closing said housing top incorporating sensor signal feed-through pins, and coil means surrounding said armature , and being actuatable in response to electrical signals from said sensors to move said armature.

Claim 36

The controller of Claim 33 in which said valve seat, said armature, said pole piece and said sensor and by-pass module are annularly spaced from interior side walls of said housing forming an annular gas passageway from said gas inlet port to said sensor and by-pass module.

Claim 37

The controller of Claim 33 including a non-planar open spring extending between said valve seat and said armature and a non-planar open spring extending between said armature and said pole piece such that said armature is suspended with radial clearance from the interior housing side-walls, and such that upon deactua- tion of said coil, said armature valve seat is spring forced toward said orifice by said springs to close said orifice.

Claim 38

The controller of Claim 33 with a dead gas volume of less than two cubic centimeters between the flow sensor and the valve stem flow orifice enabling high speed response by minimizing pressure stabilization times between the flow sensor and the valve stem flow orifice.