Vapor composition and flow sensor

• US 5,515,714 A
• Filed: 11/17/1994
• Issued: 05/14/1996
• Est. Priority Date: 11/17/1994
• Status: Expired due to Fees

• Current Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: O'Rourke, Michael J., Sultan, Michel F., Harrington, Charles R.
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): LARKIN, DANIEL SEAN
• Application Number:
  US08/341,258
• Time in Patent Office: 544 Days
• Field of Search: 73/25.01, 73/25.05, 73/204.18, 73/204.25, 73/204.26
• US Class Current: 73/25.01
• CPC Class Codes: G01D 3/028 mitigating undesired influences, e.g. temperature, pressure
• CPC Class Codes: G01F 1/6845 Micromachined devices
• CPC Class Codes: G01F 1/696 Circuits therefor, e.g. constant-current flow meters
• CPC Class Codes: G01N 27/18 caused by changes in the thermal conductivity of a surrounding material to be tested G01N27/20 takes precedence

Abstract

The present invention is directed to a single solid state thermal diffusion sensor capable of measuring both the composition and flow of gaseous vapors traveling through a duct. The sensor comprises two orthogonal sensing patterns, each having a heating element positioned equidistant between two thermistor elements. The heaters and thermistors are made from thin film platinum deposited on a thermally insulating polyimide layer having low thermal diffusivity. A sinusoidal voltage is applied to each heating element for generating oscillating thermal waves which propagate through the gaseous vapor to their respective thermistors. The thermistors of a first, transversely positioned sensing pattern are responsive to both the composition and flow of the gaseous vapor, while the thermistors of a second, longitudinally positioned sensing pattern are responsive only to the composition of the gaseous vapor. Appropriate electronic circuitry utilizes the responses of the thermistor pairs for determining the composition and flow of the gaseous vapor.

Claims

1. An apparatus for providing gaseous vapor output signals indicative of the composition and flow of the gaseous vapor traveling through a duct, the apparatus comprising:

a first sensing pattern including a first heater positioned equidistant between an upstream detector and a downstream detector, the first heater as well as the upstream and downstream detectors positioned transversely within the duct and responsive to temperature;

a second sensing pattern including a second heater positioned equidistant between a first detector and a second detector, the second heater as well as the first and second detectors positioned longitudinally within the duct and responsive to temperature; and

means for exciting the first and second heaters to generate sinusoidal thermal waves which propagate through the gaseous vapor to the upstream and downstream detectors and the first and second detectors, respectively, resulting in temperature variations and corresponding responses by the upstream, downstream, first and second detectors, wherein the responses of the upstream and downstream detectors are dependant upon the composition and flow of the gaseous vapor and the responses of the first and second detectors are dependant upon only the composition of the gaseous vapor.

2. The gaseous vapor composition and flow sensing apparatus according to claim 1, further comprising:

first signal means for providing a first signal responsive to the propagating thermal waves sensed by the upstream detector;

second signal means for providing a second signal responsive to the propagating thermal waves sensed by the downstream detector;

third signal means for providing a third signal responsive to the propagating thermal waves sensed by the first detector;

fourth signal means for providing a fourth signal responsive to the propagating thermal waves sensed by the second detector;

means for subtracting the first and second signals to obtain a difference signal;

means for adding the third and fourth signals to obtain a cumulative signal;

means for providing a gaseous vapor composition output signal responsive to the cumulative signal and indicative of a measure of the composition of the gaseous vapor; and

means for providing a first gaseous vapor flow output signal responsive to the difference signal and indicative of both the composition and flow of the gaseous vapor.

3. The gaseous vapor composition and flow sensing apparatus according to claim 2, further comprising:

means for providing a second gaseous vapor flow output signal responsive to both the difference and cumulative signals, and indicative of the flow of the gaseous vapor.

4. The gaseous vapor composition and flow sensing apparatus according to claim 1, wherein the first and second heaters, as well as the upstream, downstream, first and second detectors are formed of thin film platinum deposited on a thermally insulating polyimide layer over a silicon layer.

5. The gaseous vapor composition and flow sensing apparatus according to claim 1, wherein the upstream, downstream, first and second detectors are one of thermistors and thermocouples.

6. The gaseous vapor composition and flow sensing apparatus according to claim 1, wherein the sensing apparatus is positioned at a predetermined angle with respect to the gaseous vapor flow.