Thermocouple temperature sensor with cold junction compensation

Patent metadata

Field	Value
Publication number	US-10330538-B2
Application number	US-201715437706-A
Country	US
Kind code	B2
Filing date	Feb 21, 2017
Priority date	Feb 21, 2017
Publication date	Jun 25, 2019
Grant date	Jun 25, 2019

Abstract

A thermocouple temperature sensor has a thermocouple with first and second conductors connected at a junction and a resistance temperature device with first and second conductors. The first conductor of the resistance temperature device is connected to the first conductor of the thermocouple. A first external conductor is connected to the second conductor of the thermocouple, wherein the first external conductor is configured as a voltage sense conductor for the resistance temperature device and a voltage sense conductor for the thermocouple. A second external conductor is connected to the first conductors of the thermocouple and the resistance temperature device, wherein the second external conductor is configured as a current conductor for the resistance temperature device and a voltage sense conductor for the thermocouple. A third external conductor is connected to the second conductor of the resistance temperature device and is configured as a current conductor for the resistance temperature device.

First claim

What is claimed is:

1. A thermocouple temperature sensor comprising:
a thermocouple having first and second conductors connected at a junction;
a resistance temperature device having a first conductor and a second conductor, the first conductor of the resistance temperature device connected to the first conductor of the thermocouple;
a first external conductor connected to the second conductor of the thermocouple, wherein the first external conductor is configured as a voltage sense conductor for the resistance temperature device and a voltage sense conductor for the thermocouple;
a second external conductor connected to the first conductors of the thermocouple and the resistance temperature device, wherein the second external conductor is configured as a current conductor for the resistance temperature device while configured as a voltage sense conductor for the thermocouple; and
a third external conductor connected to the second conductor of the resistance temperature device, wherein the third external conductor is configured as a current conductor for the resistance temperature device.

2. The thermocouple temperature sensor of claim 1 further comprising a fourth external conductor connected to the second conductor of the resistance temperature device, wherein the fourth external conductor is configured as a voltage sense conductor for the resistance temperature device.

3. The thermocouple temperature sensor of claim 1 wherein the third external conductor is further configured as a voltage sense conductor for the resistance temperature device.

4. The thermocouple temperature sensor of claim 1 further comprising an external sheath such that the thermocouple and the resistance temperature device are both within the external sheath.

5. The thermocouple temperature sensor of claim 4 wherein the thermocouple is located within a portion of the external sheath that is configured to be placed in a first environment at a first temperature and the resistance temperature device is located in a second portion of the external sheath that is configured to be placed in a second environment at a second temperature.

6. The thermocouple temperature sensor of claim 1 wherein the first external conductor, the second external conductor and the third external conductor each comprise copper wires.

7. The thermocouple temperature sensor of claim 6 wherein the copper wires of the first external conductor, the second external conductor and the third external conductor are each longer than one foot.

8. The thermocouple temperature sensor of claim 1 wherein the first external conductor, the second external conductor and the third external conductor comprise terminals configured to be coupled to wires.

9. The thermocouple temperature sensor of claim 1 further comprising a transmitter connected to the thermocouple temperature sensor.

10. The thermocouple temperature sensor of claim 9 wherein the transmitter comprises EMF compensation.

11. A thermocouple capsule comprising:
an exterior sheath;
a resistance temperature device positioned in the sheath and having a first conductor and a second conductor;
a thermocouple positioned in the sheath and having a first conductor and a second conductor connected together at a junction, wherein the first conductor and the second conductor of the thermocouple have respective free ends apart from the junction and wherein the first conductor of the resistance temperature device is connected to the first conductor of the thermocouple at the free end of the first conductor of the thermocouple;
a first external conductor that is configured to both conduct current that passes through the first conductor of the resistance temperature device and to communicate a voltage from the first conductor of the thermocouple;
a second external conductor that is configured to communicate a voltage from the second conductor of the thermocouple;
a third external conductor that is configured to conduct a current that passes through the second conductor of the resistance temperature device; and
a fourth external conductor that is configured to communicate a voltage from the second conductor of the resistance temperature device.

12. The thermocouple capsule of claim 11 wherein the external conductor comprises a copper wire that is greater than one foot long.

13. The thermocouple capsule of claim 11 wherein the external conductor comprises a terminal.

14. The thermocouple capsule of claim 11 wherein the resistance temperature device is positioned in a first end of the exterior sheath and the junction of the thermocouple is positioned in a second end of the exterior sheath.

15. A method of measuring a temperature of a thermocouple positioned in a process fluid:
passing a current through a resistance temperature device using a first conductor and a second conductor;
measuring a voltage across a thermocouple using the second conductor and a third conductor;
determining a voltage produced by the resistance temperature device in response to the current using the third conductor;
determining a reference temperature based on the voltage produced by the resistance temperature device in response to the current;
using the reference temperature and the voltage across the thermocouple to determine a temperature of the thermocouple.

16. The method of claim 15 wherein determining the voltage produced by the resistance temperature device in response to the current further comprises using the first conductor.

17. The method of claim 15 wherein determining the voltage produced by the resistance temperature device in response to the current further comprises using a fourth conductor that is electrically coupled to the resistance temperature device.

18. The method of claim 15 wherein the resistance temperature device and the thermocouple are in a single sheath.

19. The method of claim 18 wherein a portion of the sheath containing the thermocouple is located in a conduit containing the process fluid and a portion of the sheath containing the resistance temperature device is located outside of the conduit.

Assignees

• Rosemount Inc

Inventors

• Rud Jason Harold
• Kassen Allen John
• Holmstadt Clarence

Classifications

• G01K1/20

  Compensating for effects of temperature changes other than those to be measured, e.g. changes in ambient temperature · CPC title

• G01K7/023

  provided with specially adapted connectors (connectors per se H01R) · CPC title

• G01K1/08 Primary

  Protective devices, e.g. casings · CPC title

• G01K7/13 Primary

  Circuits for cold-junction compensation · CPC title

• G01K7/16

  using resistive elements · CPC title