Thermal diffusion fluid flow sensor

• US 4,576,050 A
• Filed: 08/29/1984
• Issued: 03/18/1986
• Est. Priority Date: 08/29/1984
• Status: Expired due to Term

• Current Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Lambert, David K.
• Primary Examiner(s): Goldstein, Herbert
• Application Number:
  US06/645,253
• Time in Patent Office: 566 Days
• Field of Search: 73/204, 73/861.05
• US Class Current: 73/861.95
• CPC Class Codes: G01F 1/684 Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
• CPC Class Codes: G01F 1/6842 with means for influencing the fluid flow
• CPC Class Codes: G01F 1/6845 Micromachined devices
• CPC Class Codes: G01F 1/708 Measuring the time taken to traverse a fixed distance
• CPC Class Codes: G01F 1/7084 using thermal detecting arrangements

Abstract

A miniature solid state fluid flow sensor has a low diffusivity substrate, such as a polymer film, which is optionally mounted on a thermally conductive base. A resistor strip on the substrate is connected to an electrical oscillator and thus emits thermal waves which are propagated through the fluid at a rate dependent on a fluid flow component perpendicular to the strip. A thermoelectric detector, spaced from one side or each side of the strip, senses the thermal waves; and detector circuitry determines the time or phase shift due to fluid flow.

Claims

1. A gas flow sensor for location contiguous to a body of gaseous fluid subject to flow to be measured, comprising:

a substrate having a thermal diffusivity substantially less than that of the fluid and having a thermal conductivity substantially greater than the fluid;

a thermal oscillation source on the surface of the substrate for generating thermal oscillations in the fluid, whereby thermal oscillations are propagated through still fluid at a first rate and through flowing fluid at a second rate dependent on fluid flow to substrate surface locations spaced from the source;

thermal oscillation detector means on the substrate surface near the oscillation source for providing at least one signal corresponding to the thermal oscillations at the detector means; and

signal responsive means coupled to the detector means for sensing the first and second rates and producing an output correlated to the mass gas flow near the substrate surface.

2. A gas flow sensor for location contiguous to a body of gaseous fluid subject to flow to be measured, comprising:

a substrate having a thermal diffusivity substantially less than that of the fluid and having a thermal conductivity substantially greater than the fluid;

a thermal oscillation source comprising resistor strip means on the surface of the substrate for generating thermal oscillations in the fluid, whereby thermal oscillations are propagated through still fluid at a first rate and through flowing fluid at a second rate dependent on fluid flow to substrate surface locations laterally spaced from the source;

electrical current supply means coupled to the resistor strip means for producing current pulses to energize the thermal oscillation source;

thermal oscillation detector means on the substrate surface laterally spaced from the oscillation source for providing at least one signal corresponding to the thermal oscillations at the detector means; and

signal responsive means coupled to the oscillation source and the detector means for sensing the first and second rates and producing an output correlated to the mass gas flow near the substrate surface.

3. A gas flow sensor for location contiguous to a body of gaseous fluid subject to fow to be measured, comprising:

a substrate having a thermal diffusivity substantially less than that of the fluid and having a thermal conductivity substantially greater than the fluid;

a thermal oscillation source comprising resistor strip means on the surface of the substrate for generating thermal oscillations in the fluid, whereby thermal oscillations are propagated through still fluid at a first rate and through flowing fluid at a second rate dependent on fluid flow to the substrate surface locations laterally spaced from the source;

electrical current supply means coupled to the resistor strip means for producing current pulses to energize the thermal oscillation source;

detectors of the fluid thermal oscillations on the substrate surface laterally spaced from each side of the oscillation source for providing signals corresponding to the thermal oscillations at the detector locations; and

means responsive to the current supply means and the detector signals for sensing the first and second rates and producing an output correlated to the mass gas flow near the substrate surface.

4. A fluid flow sensor for location adjacent a body of fluid subject to flow to be measured, comprising:

a substrate having a thermal diffusivity substantially less than that of the fluid;

a thermal oscillation source comprising a pair of spaced parallel resistor strips on the surface of the substrate for generating thermal oscillations in the fluid, whereby thermal oscillations are propagated through the fluid at a rate dependent on the fluid flow to the substrate surface locations spaced from the source;

electrical current means coupled to the resistor strips for producing current pulses to energize the thermal oscillation source;

a detector of the fluid thermal oscillations on the substrate surface between the resistor strips of the oscillation source for providing a signal corresponding to the thermal oscillations at the detector location; and

means responsive to the detector signal for producing an output correlated to the fluid flow near the substrate surface.

5. A fluid flow sensor for location adjacent a body of fluid subject to flow to be measured, comprising:

a polymer film substrate having a thermal diffusivity substantially less than that of the fluid;

a thermal oscillation source comprising a thin film resistor on the surface of the substrate for generating thermal oscillations in the fluid, whereby thermal oscillations are propagated through the fluid at a rate dependent on fluid flow to substrate surface locations spaced from the source;

thin film thermoelectric detector means responsive to the fluid thermal oscillations mounted on the substrate surface near the oscillation source for providing at least one signal corresponding to the thermal oscillations at the detector means location; and

means responsive to the detector means signal for producing an output correlated to the fluid flow near the substrate surface.

6. A fluid flow sensor as claimed in claim 5, wherein the polymer film is mounted on a thermally conductive base to allow high thermal oscillation amplitude while maintaining a low maximum source temperature.

7. An air flow sensor for location adjacent an airstream subject to flow to be measured, comprising:

a silicon base for providing sensor heat sink properties;

a polyimide film substrate having a thermal diffusivity substantially less than that of the air mounted on the silicon base;

a thin film elongated thermal oscillation source on the surface of the substrate and thermally coupled to the air for generating thermal oscillations in the air, whereby thermal oscillations are propagated through the air at a rate dependent on air flow to substrate surface locations spaced from the source;

thin film thermoelectric detector means responsive to the air thermal oscillations and mounted on the substrate surface near the oscillation source for providing a signal corresponding to the thermal oscillations at the detector means location; and

electronic means responsive to the detector means signal for producing an output correlated to the air flow near the substrate surface.

8. An air flow sensor for location adjacent an airstream subject to flow to be measured, comprising:

a silicon base for providing sensor heat sink properties and adapted to contain integrated circuitry;

a polyimide film substrate having a thermal diffusivity substantially less than that of the air mounted on the silicon base;

a thin film elongated thermal oscillation source on the surface of the substrate and thermally coupled to the air for generating thermal oscillations in the air, whereby thermal oscillations are propagated through the air at a rate dependent on air flow to substrate surface locations spaced from the source;

thin film thermoelectric detector means responsive to the air thermal oscillations and mounted on the substrate surface near the oscillation source for providing a signal corresponding to the thermal oscillations at the detector means location;

integrated circuitry in the silicon base containing oscillator means coupled to the oscillation source; and

electronic means coupled to the detector means for producing an output correlated to the air flow near the substrate surface.

9. A fluid flow sensor for location contiguous to a body of fluid subject to flow to be measured, comprising:

a substrate having a thermal diffusivity substantially less than that of the fluid;

a first thermal oscillation source on the surface of the substrate for generating thermal oscillations in the fluid, whereby thermal oscillations are propagated through the fluid at a rate dependent on fluid flow to substrate surface locations spaced from the first source;

first thermal oscillation detector means on the substrate surface near the first oscillation source for providing at least one signal corresponding to the thermal oscillations at the first detector means;

a second thermal oscillation source on the substrate surface for generating thermal oscillations in the fluid, and second thermal oscillation detector means on the substrate surface near the second oscillation source, the second source and second detector means being positioned to detect the propagation of thermal oscillations independently of fluid flow rate for providing a reference signal; and

signal responsive means coupled to the first and second detector means for producing an output correlated to the fluid flow near the substrate surface, which output is compensated for temperature and pressure effects on thermal oscillation propagation rate.

10. A fluid flow sensor for location adjacent a body of fluid subject to flow to be measured, comprising:

a polymer film substrate having a thermal diffusivity substantially less than that of the fluid;

a primary thermal oscillation source comprising a thin film resistor on the surface of the substrate for generating thermal oscillations in the fluid, whereby thermal oscillations are propagated through the fluid at a rate dependent on fluid flow to substrate surface locations spaced from the primary source;

primary thin film thermoelectric detector means responsive to the fluid thermal oscillations mounted on the substrate surface near the primary oscillation source for providing at least one primary signal corresponding to the thermal oscillations at the primary detector means location;

a reference thermal oscillation source on the substrate surface for generating thermal oscillations in the fluid and reference thermal oscillation detector means on the substrate surface near the reference oscillation source, the reference source and reference detector means being positioned to detect the propagation of thermal oscillations in a direction having a different component of fluid flow for providing a reference signal; and

means responsive to the primary and reference signals for producing an output correlated to the fluid flow near the substrate surface, which output is compensated for temperature and pressure effects.