Self-verifying temperature sensor

• US 5,887,978 A
• Filed: 09/15/1997
• Issued: 03/30/1999
• Est. Priority Date: 08/23/1996
• Status: Expired due to Fees

• Current Assignee: Accutru International
• Original Assignee: Accutru International
• Inventors: Brannon, C. Tom, Transier, Lee, Conner, Bernard L., Cannon, Collins P., Lunghofer, James G.
• Primary Examiner(s): Biegel, Ronald
• Assistant Examiner(s): AMROZOWICZ, PAUL DOUGLAS
• Application Number:
  US08/929,985
• Time in Patent Office: 561 Days
• Field of Search: 374/163, 374/178, 374/179, 374/180, 374/181, 374/183, 374/184, 374/185
• US Class Current: 374/179
• CPC Class Codes: G01K 15/00 Testing or calibrating of thermometers
• CPC Class Codes: G01K 7/00 Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat giving results other than momentary value of temperature G01K3/00 ; Power supply therefor, e.g. using thermoelectric elements

Abstract

A self-verifying temperature sensor and method for measuring and verifying the true thermodynamic temperature of a system. The sensor is constructed of various combinations of the following temperature-dependent elements: thermoelements, resistive elements, capacitive elements and other inductive elements. In the preferred embodiment, the sensor is constructed of resistive element connected between four thermoelement wires. A fifth thermoelement wire is connected to the resistive element. The sensor produces a data signature from various voltage, resistance, inductance, and capacitance measurements. Measurement electronics collect and condition the data signature. A computer analyzes the data signature and provides the system operator with a verified sensor temperature, thus, allowing the system operator to recognize and account for drift or decalibration of the sensor. The self-verifying temperature sensor can also be recalibrated insitu, thereby eliminating the necessity of sensor removal to verify recalibration.

Claims

1. A self-verifying temperature sensor, comprising:

a thermocouple for emitting primary signals;

a secondary sensor for emitting secondary signals, said secondary sensor including at least one impedance element; and

a processor for determining a verified temperature from the primary and secondary signals.

2. The sensor of claim 1, wherein the thermocouple comprises:

a first temperature-dependent element made from a first material; and

a second temperature-dependent element made from a second material different than the first material.

3. The sensor of claim 2 wherein the thermocouple is a first thermocouple and wherein the secondary sensor further comprises:

a second thermocouple having third and fourth temperature-dependent elements made from different materials and joined at a junction point; and

wherein the impedance element has a first end coupled to the junction point and a second end coupled to the first thermocouple.

4. The sensor of claim 3, wherein the secondary sensor further comprises:

a thermoelement wire extending from a point on the impedance element between the second thermocouple and the first thermocouple.

5. The sensor of claim 1, wherein the processor comprises:

means for converting the primary signals into a primary temperature value;

means for converting the secondary signals into a calibration reference; and

means for comparing the primary temperature value with the calibration reference to produce a confidence value.

6. The sensor of claim 5, wherein the processor further comprises:

recalibration means for recalibrating the sensor when the confidence value is below a predetermined level.

7. The sensor of claim 5, wherein the processor further comprises:

display means for displaying the primary temperature value and the confidence value.

24. The sensor of claim 1, wherein said processor comprises a computer.

8. A sensor element in a self-verifying temperature sensor, the sensor element comprising:

a first temperature-dependent element having a first failure mode;

a second temperature-dependent element having a second failure mode; and

an impedance element having a third failure mode;

wherein the first and second temperature-dependent elements and the impedance element are electrically connected and collectively produce a data signature defining a verifiable temperature.

9. The sensor element of claim 8 wherein the first and second failure modes are different than the third failure mode.

10. The sensor element of claim 9, wherein the first and second temperature-dependent elements each comprise:

a first thermoelement wire of a first composition; and

a second thermoelement wire of a second composition, the first and second thermoelement wires having said impedance element coupled therebetween.

11. The sensor element of claim 8, wherein the impedance element comprises a resistor.

12. The sensor element of claim 8, further comprising:

a third temperature-dependent element electrically connected to the impedance element and having a fourth failure mode, wherein the third temperature-dependent element also produces the data signature.

13. A method of measuring a system temperature utilizing a self-verifying temperature sensor, the method comprising the steps of:

obtaining a primary data signature from a primary sensor;

obtaining a secondary data signature from a secondary sensor;

determining a primary system temperature from the primary data signature;

determining a calibration reference from the secondary data signature; and

comparing the primary system temperature to the calibration reference to obtain a verified system temperature.

14. The method of claim 13, further comprising the step of:

determining a degradation level of the self-verifying temperature sensor from the primary data signature and the secondary data signature.

15. The method of claim 14, further comprising the step of:

recalibrating the self-verifying temperature sensor to compensate for the degradation level.

16. The method of claim 13, wherein the step of obtaining a secondary data signature comprises the step of:

selecting signals generated by a plurality of secondary sensors.

17. The method of claim 15, wherein the recalibrating step comprises the steps of:

selecting a new primary sensor; and

selecting a new secondary sensor.

18. A sensor element, the sensor element comprising:

a first sensor for measuring temperature having a first failure mode; and

an impedance element for measuring temperature having a second failure mode, wherein the second failure mode is different than the first failure mode.

19. The sensor element of claim 18, wherein the first sensor comprises a first thermocouple.

20. The sensor element of claim 19, wherein the first thermocouple comprises:

a first temperature-dependent element made from a first material; and

a second temperature-dependent element made from a second material different than the first material.

21. The sensor of claim 20, wherein said impedance element is connected between said first temperature-dependent element and said second temperature-dependent element.

22. The sensor element of claim 21, further comprising a third temperature-dependent element for measuring temperature connected to said impedance element, said third temperature-dependent element having a third failure mode, wherein the third failure mode is different than the first or second failure mode.

23. The sensor element of claim 22, wherein the third temperature-dependent element is selected from the group consisting of a resistor, a capacitor, an inductor, a diode, a crystal, and a semiconductor.

25. A method of measuring a system temperature utilizing a self-verifying temperature sensor, the method comprising the steps of:

obtaining a primary data signature from a primary sensor;

obtaining a secondary data signature from a secondary sensor, said secondary sensor comprising at least one impedance element;

determining a primary system temperature from the primary data signature;

determining a calibration reference from the secondary data signature; and

comparing the primary system temperature to the calibration reference to obtain a verified system temperature.

26. The method of claim 25, further comprising the step of:

determining the degradation level of the self-verifying temperature sensor from the primary data signature and the secondary data signature.

27. The method of claim 26, further comprising the step of:

recalibrating the self-verifying temperature sensor to compensate for the degradation level.

28. The method of claim 25, wherein the step of obtaining a secondary data signature comprises the steps of:

selecting signals generated by plurality of secondary sensors.

29. The method of claim 27, wherein the recalibrating step comprises the steps of:

selecting a new primary sensor; and

selecting a new secondary sensor.

30. A temperature sensor, comprising:

an impedance element; and

a first thermocouple, comprising;

a first thermoelement made from a first temperature-dependent material; and

a second thermoelement made from a second temperature-dependent material and joined with the first thermoelement at a first junction;

a second thermocouple, comprising;

a third thermoelement made from the first temperature-dependent material; and

a fourth thermoelement made from the second temperature-dependent material and joined with the third thermoelement at a second junction;

a protection tube encasing the impedance element and the first and second junctions, the protection tube maintaining the impedance element and the first and second junctions in an isothermal relationship;

measurement electronics coupled to the impedance element, the first thermocouple, and the second thermocouple, the measurement electronics obtaining a data signature therefrom; and

a computer coupled to the measurement electronics and receiving the data signature therefrom, the computer converting the data signature into a temperature value and a confidence value.

31. The sensor of claim 30, wherein the data signature comprises:

a primary data signature indicating the temperature value; and

a secondary data signature indicating the confidence value.

32. The sensor of claim 31, wherein the measurement electronics further comprise:

a primary A/D converter receiving the primary data signature and outputting a digital primary signal to the computer;

a MUX receiving the secondary data signature and outputting selected signals therefrom; and

a secondary A/D converter receiving the selected signals from the MUX and outputting a digital secondary signal to the computer.

33. The sensor of claim 30, wherein the impedance element is a resistor.