Thermal conductivity gauge
A thermal conductivity gauge measures gas pressure within a chamber. A sensor wire and a resistor form a circuit coupled between a power input and ground, where the sensor wire extends into the chamber and connects to the resistor via a terminal. A controller adjusts the power input, as a function of a voltage at the terminal and a voltage at the power input, to bring the sensor wire to a target temperature. Based on the adjusted power input, the controller can determine a measure of the gas pressure within the chamber.
1. A thermal conductivity gauge for measuring gas pressure, comprising:
a first resistor within a chamber coupled to a terminal;
a second resistor in series with the first resistor and external to the chamber;
an analog-to-digital converter (ADC) configured to determine a voltage across one of the first and second resistors; and
digital circuitry configured to determine a measure of gas pressure within the chamber based on the voltage across one of the first and second resistors;
wherein the first resistor is coupled to a grounded envelope encompassing a volume of the chamber.
2. The gauge of claim 1 , wherein the voltage across one of the first and second resistors is the voltage across the second resistor.
3. The gauge of claim 1 , wherein the second resistor is coupled between the terminal and an electrical input receiving a power input.
4. The gauge of claim 1 , wherein the first and second resistors have an equivalent resistance at a target temperature.
5. The gauge of claim 1 , wherein the first resistor is coupled to the envelope via a shield extending through the volume of the chamber.
6. The gauge of claim 1 , wherein the first resistor is supported within a removable housing extending between the terminal and a ground.
7. A thermal conductivity gauge for measuring gas pressure, comprising:
a first resistor within a chamber coupled to a terminal;
a second resistor in series with the first resistor and external to the chamber;
an analog-to-digital converter (ADC) configured to determine a voltage across one of the first and second resistors;
digital circuitry configured to determine a measure of gas pressure within the chamber based on the voltage across one of the first and second resistors; and
a controller configured to 1) determine a compensation factor based on an envelope temperature external to the chamber and 2) determine the measure of gas pressure as a function of the compensation factor.
8. The gauge of claim 7 , further comprising a third resistor and a switch connected in parallel with the second resistor, the controller selectively enabling the switch.
9. The gauge of claim 7 , further comprising an ion gauge within the chamber.
10. The gauge of claim 9 , wherein feedthroughs of the gauge and the ion gauge extend through a common feedthrough flange coupled to the chamber.
11. The gauge of claim 10 , wherein the gauge includes a single feedthrough of the feedthrough flange, the terminal being the single feedthrough.
12. The gauge of claim 11 , wherein the controller is configured to selectively enable the ion gauge in response to detecting the measure of gas pressure being below a target threshold.
13. The gauge of claim 11 , wherein the controller is further configured to determine a compensation factor based on heat generated by the ion gauge, the controller configured to determine the measure of gas pressure as a function of the compensation factor.
14. The gauge of claim 11 , wherein the controller is configured to selectively disable the ion gauge in response to detecting the measure of gas pressure being above a target threshold.
15. A method of measuring gas pressure, comprising:
applying a power input through a first resistor and a second resistor connected in series, the first resistor being coupled to a terminal within a chamber, the second resistor being external to the chamber;
determining, via an analog-to-digital converter (ADC), a voltage across one of the first and second resistors; and
determining, via digital circuitry, a measure of gas pressure within the chamber based on the voltage across one of the first and second resistors;
wherein the first resistor is coupled to a grounded envelope encompassing a volume of the chamber.
16. The method of claim 15 , wherein the voltage across one of the first and second resistors is the voltage across the second resistor.
17. The method of claim 15 , wherein the first and second resistors have an equivalent resistance at a target temperature.
18. The method of claim 15 , wherein the first resistor is coupled to the envelope via a shield extending through the volume of the chamber.
19. The method of claim 15 , further comprising selectively connecting a third resistor in parallel to the second resistor based on the voltage at the terminal.
20. The method of claim 15 , further comprising selectively enabling an ion gauge in response to detecting the measure of gas pressure being below a target threshold.
21. The method of claim 15 , further comprising determining a compensation factor based on heat generated by an ion gauge, the measure of gas pressure being determined as a function of the compensation factor.
22. The method of claim 15 , wherein the first resistor is supported within a removable housing extending between the terminal and a ground.
23. A method of measuring gas pressure, comprising: applying a power input through a first resistor and a second resistor connected in series, the first resistor being coupled to a terminal within a chamber, the second resistor being external to the chamber; determining, via an analog-to-digital converter (ADC), a voltage across one of the first and second resistors;
and determining, via digital circuitry, a measure of gas pressure within the chamber based on the voltage across one of the first and second resistors; determining a compensation factor based on an envelope temperature external to the chamber, and determining the measure of gas pressure as a function of the compensation factor.
24. A thermal conductivity gauge for measuring gas pressure, comprising:
a circuit comprising a first resistor and a second resistor coupled in series, the first resistor being positioned within a chamber, the second resistor being external to the chamber; and
an analog-to-digital converter (ADC) configured to determine a voltage across one of the first and second resistors; and
digital circuitry configured to determine a measure of gas pressure within the chamber based on the voltage across one of the first and second resistors;
wherein the first resistor is coupled to a grounded envelope encompassing a volume of the chamber.