Thermal vacuum gauge

• US 7,613,586 B2
• Filed: 01/16/2007
• Issued: 11/03/2009
• Est. Priority Date: 01/16/2007
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Higashi, Robert E.
• Primary Examiner(s): Lau; Tung S
• Assistant Examiner(s): Sun; Xiuquin
• Application Number:
  US11/623,561
• Publication Number:
  US 20080168842A1
• Time in Patent Office: 1,022 Days
• Field of Search: 702/138, 737/55, 737/53
• US Class Current: 702/138
• 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; and

further comprising;

a heating element situated in the heating structure;

a temperature sensing element situated in the sensing structure; and

a sensing and control electronics circuit connected to the temperature sensing element and the heating element; and

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.

2. The sensor of claim 1, 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.

3. The sensor of claim 2, wherein the control circuit comprises:

a processor; and

a user interface connected to the processor.

4. 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; and

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; and

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.

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

placing a heater in a volume;

placing a temperature sensor proximate to but distinct from 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;

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

situating the heater in a first structure;

situating the temperature sensor in the first structure;

situating a second structure on a substrate; and

situating the first structure on the second structure; and

wherein;

$T_S-T_{\mathrm{Sub}}\propto <br><br>\frac{P_{\mathrm{heat}}}{K_{\mathrm{support}}*A_{\mathrm{support}}+K_{\mathrm{gas}}*A_{\mathrm{gas}}};<br><br>$

T_s is a temperature detected by the sensor;

T_sub is a temperature of the substrate;

P_heat is an amount of power to the heater;

K_support is a thermal conductivity constant of the second structure;

A_support is a cross-section area of the second structure;

K_gas is a thermal conductivity constant of the gas in the volume; and

A_gas is a surface area of the first structure exposed to the gas.

6. A pressure sensor comprising:

a substrate;

a heating structure situated on the substrate; and

a sensing structure proximate to but distinct from 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; and

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; and

wherein;

$T_S-T_{\mathrm{Sub}}\approx <br><br>\frac{K_{\mathrm{gas}}*A_{\mathrm{gas}<br><br><br><br>2}*C_{\mathrm{config}}}{K_{\mathrm{support}}*A_{\mathrm{support}<br><br><br><br>17}+K_{\mathrm{gas}}*A_{\mathrm{gas}<br><br><br><br>2}}*\left(\frac{P_{\mathrm{heat}}}{K_{\mathrm{support}}*A_{\mathrm{support}<br><br><br><br>15}+K_{\mathrm{gas}}*A_{\mathrm{gas}<br><br><br><br>1}}\right)$

T_s is a temperature detected by the sensing structure;

T_sub is a temperature of the substrate;

K_gas is a thermal conductivity constant of the ambient gas;

A_gas1 is a surface area of the heating structure in contact with the ambient gas;

A_gas2 is a surface area of the sensing structure in contact with the ambient gas;

K_support is a thermal conductivity constant of the first and second support structures;

C_config is a configuration factor of the pressure sensor;

P_heat is an amount of power consumed by the heating structure;

A_support1 is a cross section of the first support structure; and

A_support2 is a cross section of the second support structure.