PROCESS VARIABLE TRANSMITTER WITH THERMOCOUPLE POLARITY DETECTION

• US 20110299567A1
• Filed: 06/07/2010
• Published: 12/08/2011
• Est. Priority Date: 06/07/2010
• Status: Active Grant

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Rud, Jason H., Holmstadt, Clarence
• Granted Patent: US 8,864,378 B2
• Time in Patent Office: Days
• US Class Current: 374/181
• CPC Class Codes: G01K 7/026 Arrangements for signalling failure or disconnection of thermocouples

Abstract

A process variable transmitter for measuring a temperature of an industrial process, includes a first electrical connector configured to couple to a first wire of a thermocouple, the first electrical connector includes a first electrode and a second electrode. The first and second electrodes are configured to electrically couple to the first wire of the thermocouple. A second electrical connector is configured to couple to a second wire of the thermocouple, the second electrical connector includes a third electrode and a fourth electrode. The third and fourth electrodes are configured to electrically couple to the second wire of the thermocouple. The second wire is of a different material than the first wire. Measurement circuitry is coupled to the first and second electrical connectors configured to provide an output related to a temperature of the thermocouple. The measurement circuitry is further configured to identify polarity of thermocouple based upon at least one measurement taken between at least two of the first, second, third and fourth electrodes.

Claims

1. A process variable transmitter for measuring a temperature of an industrial process, comprising:

a first electrical connector configured to couple to a first wire of a thermocouple, the first electrical connector comprising a first electrode and a second electrode, the first and second electrodes configured to electrically couple to the first wire of the thermocouple;

a second electrical connector configured to couple to a second wire of the thermocouple, the second electrical connector comprising a third electrode and a fourth electrode, the third and fourth electrodes configured to electrically couple to the second wire of the thermocouple, the second wire of a different material than the first wire; and

measurement circuitry coupled to the first and second connectors configured to provide an output related to a temperature of the thermocouple, the measurement circuitry further configured to identify polarity of thermocouple based upon at least one voltage measurement taken between at least two of the first, second, third and fourth electrodes.

2. The process variable transmitter of claim 1 wherein the measurement circuitry is configured to identify a type of the thermocouple based upon the at least one voltage measurement.

3. The process variable transmitter of claim 2 wherein the measurement circuitry is configured to provide an output if the identified type of the thermocouple is different than a configuration stored in the measurement circuitry.

4. The process variable transmitter of claim 1 wherein the first and second electrodes comprise different materials.

5. The process variable transmitter of claim 4 wherein the third and fourth electrodes comprise different materials.

6. The process variable transmitter of claim 5 wherein the second and fourth electrodes comprise the same material.

7. The process variable transmitter of claim 1 wherein the second and fourth electrodes comprise a thermocouple material.

8. The process variable transmitter of claim 1 wherein the measurement circuitry is configured to provide an output to an operator based upon an identification of reverse polarity of the thermocouple.

9. The process variable transmitter of claim 1 wherein the measurement circuitry is configured to compensate the output related to the temperature of the thermocouple based upon the polarity of the thermocouple.

10. The process variable transmitter of claim 1 wherein the output from the measurement circuitry is provided on a process control loop.

11. The process variable transmitter of claim 1 wherein the measurement circuitry compensates a temperature measurement based upon a voltage measured across the first and second electrical connectors generated at a junction between the first and second wires of the thermocouple, the compensation based upon a voltage measured between at least one of the first and second electrodes and the first wire of the thermocouple and thereby providing cold junction compensation to the output related to the temperature.

12. The process variable transmitter of claim 1 including a multiplexer configured to selectively couple pairs of electrical connections from the first, second, third and fourth electrodes to an analog to digital converter.

13. A method in a process variable transmitter for identifying a polarity of a thermocouple coupled to a process variable transmitter of an industrial process, comprising:

connecting a first electrical connector to a first wire of a thermocouple, the first electrical connector comprising a first electrode and a second electrode;

connecting a second electrical connector to a second wire of the thermocouple, the second electrical connector comprising a third electrode and fourth electrode, the second wire of a material which is different than the first wire;

identifying a polarity of the thermocouple based upon the voltage measured between at least two of the first, second, third and fourth electrodes.

14. The method of claim 13 wherein the first and second electrodes comprise different materials.

15. The method of claim 14 wherein the third and fourth electrodes comprise different materials.

16. The method of claim 15 wherein the second and fourth electrodes comprise the same material.

17. The method of claim 13 wherein the second and fourth electrodes comprise a thermocouple material.

18. The method of claim 13 including alerting an operator in response to identifying a reverse polarity of the thermocouple.

19. The method of claim 13 including compensating an output related to the temperature of the thermocouple based upon identifying the polarity of the thermocouple.

20. The method of claim 13 including outputting on a process control loop.

21. The method of claim 13 including compensating a temperature measured based upon a voltage across the first and second electrical connectors generated at a junction between the first and second wires of the thermocouple, the compensating based upon a voltage measured between at least one of the first and second electrodes and the first wire of the thermocouple and thereby providing cold junction compensation.