THERMAL VACUUM GAUGE

• US 20080168842A1
• Filed: 01/16/2007
• Published: 07/17/2008
• Est. Priority Date: 01/16/2007
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Higashi, Robert E.
• Granted Patent: US 7,613,586 B2
• Time in Patent Office: Days
• US Class Current: 73/755
• CPC Class Codes: G01L 11/002 by thermal means, e.g. hypsometer
• CPC Class Codes: G01L 21/10 by measuring variations in the heat conductivity of the medium, the pressure of which is to be measured

Abstract

A system for determining a gas pressure or gauging a vacuum in a hermetically sealed enclosure. One or more heater structures and one or more temperature sensor structures situated on a substrate may be used in conjunction for measuring a thermal conductivity of a gas in the enclosure. Each heater has significant thermal isolation from each sensor structure. Electronics connected to each heater and sensor of their respective structures may provide processing to calculate the pressure or vacuum in the enclosure. The enclosure may contain various electronic components such as bolometers.

Claims

1. A pressure sensor comprising:

a substrate;

a heating structure situated on the substrate; and

a sensing structure proximate to the heating structure and situated on the substrate; and

wherein the pressure of an ambient gas is determined by an amount of thermal conduction between the heating structure and the sensing structure.

2. The sensor of claim 1, further comprising:

a first support structure attached to the substrate and to the heating structure; and

a second support structure attached to the substrate and the sensing structure.

3. The sensor of claim 2, wherein the first and second support structures are for holding the heating and sensing structures apart from the substrate at a certain distance.

4. The sensor of claim 1, further comprising:

a heating element situated in the heating structure; and

a temperature sensing element situated in the sensing structure.

5. The sensor of claim 4, further composing sensing and control electronics circuit connected to the temperature sensing element and the heating element.

6. The sensor of claim 2, wherein:

the heating structure has a first surface exposed to an ambient gas;

the sensing structure has a second surface exposed to an ambient gas; and

the first and second support structures have first and second cross-section areas.

7. The sensor of claim 5, wherein the sensing and control electronics circuit comprises:

a first resistor having a first end for connection to a source terminal, and having a second end;

a second resistor having a first end connected to the second end of the first resistor, and having a second end for connection to a reference terminal;

a third resistor having a first end connected to a first end of the temperature sensing element and a second end for connection to the reference terminal; and

an amplifier having a first input connected to the second end of the first resistor, and a second input connected to the second end of the sensing element, and having an output.

8. The sensor of claim 7, wherein the sensing and control electronics circuit further comprises a control circuit having an input connected to the output of the amplifier and having an output connected to one end of the heating element.

9. The sensor of claim 8, wherein the control circuit comprises:

a processor; and

a user interface connected to the processor.

10. The sensor of claim 2, wherein a temperature of the sensing structure minus a substrate temperature is approximately equal to a product of a first product that is a product of an ambient gas thermal conductivity constant times an area of a surface of the sensing structure times a sensor configuration constant divided by a first and second support structure thermal conductivity constant times an area of the second support structure plus the ambient gas thermal conductivity constant times the area of the second support structure, and a second product that is input power to the heating structure divided by a product of first and second support structure thermal conductivity constant times an area of the first support structure plus the ambient gas thermal conductivity constant times an area of the heating structure.

11. A method for measuring a pressure in a volume comprising:

a placing a heater in a volume;

placing a temperature sensor proximate to the heater in the volume;

providing power to the heater;

turning on the heater to emanate heat in the volume;

attaining a temperature indicating signal from the temperature sensor;

determining a thermal conductivity constant in the volume according to a level of thermal conduction between the heater and the temperature sensor; and

determining the pressure in the volume according to the thermal conductivity of a gas in the volume.

12. The method of claim 11, wherein a level of thermal conduction between the heater and the temperature sensor is determined approximately from a formula having a temperature of the temperature sensor minus a temperature of a substrate being about equal to (a gas thermal conductivity constant multiplied by a surface area of the temperature sensor) multiplied by a configuration constant divided by (the gas thermal conductivity constant multiplied by the surface area of the temperature sensor) multiplied by a power input to the heater divided by (the gas thermal conductivity constant multiplied by a surface area of the heater).

13. The method of claim 12, wherein:

the configuration constant represents an arrangement comprising the heater, the temperature sensor and the volume; and

given values of the temperature of the temperature sensor, the temperature of the substrate, gas thermal conductivity constant, surface area of the heater, surface area of the temperature sensor, and the configuration constant, a level of thermal conduction between the heater and the temperature sensor is determinable and/or calculatable, which implies an approximate pressure of the gas or an indication of a vacuum in the volume.

14. The method of claim 11, wherein the volume is enclosed by a sealed enclosure.

15. A vacuum gauging system comprising:

at least one heater situated in a volume; and

at least one temperature sensor situated in a volume; and

wherein a vacuum in the volume is gauged according to a measured amount of thermal conduction between the heater and the temperature sensor.

16. The system of claim 15, wherein:

the thermal conduction is based on a gas in the volume; and

reduced thermal conduction indicates less gas and improved vacuum in the volume.

17. The system of claim 15, further comprising:

a substrate;

a first support for holding the heater relative to the substrate; and

a second support for holding the temperature sensor relative to the substrate.

18. The system of claim 17, wherein:

the first support minimizes thermal conduction between the heater and the substrate; and

the second support minimizes thermal conduction between the temperature sensor and the substrate.

19. The system of claim 15, wherein the volume is within a sealed enclosure.

20. The system of claim 19, wherein the sealed enclosure comprises a bolometer.