ONLINE CALIBRATION OF A TEMPERATURE MEASUREMENT POINT

• US 20130182741A1
• Filed: 03/09/2013
• Published: 07/18/2013
• Est. Priority Date: 06/11/2009
• Status: Active Grant

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Engelstad, Loren Michael, Bauschke, Dirk Willy, Rud, Jason Harold
• Granted Patent: US 9,250,141 B2
• Time in Patent Office: Days
• US Class Current: 374/1
• CPC Class Codes: G01K 1/14 Supports; Fastening devices; Arrangements for mounting thermometers in particular locations
• CPC Class Codes: G01K 15/00 Testing or calibrating of thermometers
• CPC Class Codes: G01K 15/005 Calibration

Abstract

A method for calibrating a transmitter with measurement circuitry electrically connected to first and second input terminals includes connecting a primary temperature sensor to the first input terminal and connecting a calibrated reference device to the second input terminal. The measurement circuitry is calibrated with respect to the first input terminal according to signals received from the second input terminal while measuring temperature according to signals received from the first input terminal.

Claims

1. A method for calibrating a transmitter with measurement circuitry electrically connected to first and second input terminals, the method comprising:

connecting a primary temperature sensor to the first input terminal;

connecting a calibrated reference device to the second input terminal; and

calibrating accuracy of the measurement circuitry with respect to the first input terminal according to signals received from the second input terminal while measuring temperature according to signals received from the first input terminal.

2. The method of claim 1, wherein the calibrated reference device is a calibrated temperature sensor.

3. The method of claim 2, and further comprising:

inserting the primary temperature sensor and the calibrated temperature sensor into a thermowell prior to calibrating.

4. The method of claim 3, wherein the primary temperature sensor is inserted into the thermowell through a first passage and the calibrated temperature sensor is inserted into the thermowell through a second passage.

5. The method of claim 2, wherein accuracy of the measurement circuitry is calibrated in response to sensing that the calibrated temperature sensor has a temperature that is stable or has a predictable trend.

6. The method of claim 2, wherein accuracy of the measurement circuitry is calibrated based upon at least two measurements of the primary temperature sensor and at least two measurements of the calibrated temperature sensor.

7. The method of claim 6, wherein accuracy of the measurement circuitry is calibrated based upon a first temperature measurement taken when the calibrated temperature sensor has a temperature in a first predetermined range and a second temperature measurement taken when the calibrated temperature sensor has a temperature in a second predetermined range.

8. The method of claim 1, wherein the calibrated reference device is a reference calibration tool that generates a measureable electrical parameter with a predetermined value.

9. The method of claim 8, wherein the measureable electrical parameter is resistance or voltage.

10. The method of claim 9, wherein calibrating comprises:

measuring the measurable electrical parameter and generating a measured value with the measurement circuitry;

transmitting an actual predetermined value to the measurement circuitry;

comparing the measured value to the actual predetermined value and generating a corresponding calibration adjustment; and

calibrating the measurement circuitry based upon the corresponding calibration adjustment.

11. The method of claim 1, and further comprising:

initializing calibration of the measurement circuitry with a first user input; and

confirming calibration adjustment one or more trim values of the measurement circuitry with a second user input.

12. The method of claim 1, and further comprising:

measuring temperature with the primary temperature sensor prior to connecting the calibrated reference device disconnecting the calibrated reference device from the second input terminal; and

measuring temperature with the primary temperature sensor after disconnecting the calibrated reference device.

13. A temperature transmitter, comprising:

first and second input terminals;

a multiplexer comprising first and second channels electrically connected to each of the first and second input terminals, respectively;

an analog-to-digital converter electrically connected to the multiplexer; and

a microprocessor electrically connected to the analog-to-digital converter, wherein the microprocessor is configured to calculate a first temperature value based upon signals received from the first channel, while concurrently calibrating measurement programming for the first channel in the microprocessor according to signals received from the second channel to correct error in the measurement programming.

14. The temperature transmitter of claim 13, wherein the multiplexer comprises a third channel, and further comprising:

a third input terminal electrically connected to the third channel of the multiplexer, wherein the microprocessor is further configured to calculate first and second temperature values based upon signals received from the first and second channels, respectively, while concurrently calibrating measurement programming for the first and second channels in the microprocessor according to signals received from the third channel to correct error in the measurement programming.

15. The temperature transmitter of claim 13, wherein the microprocessor calibrates according to the third channel in response to a first user input received from a first user interface and according to the second channel in response to a second user input received from a second user interface.

16. The temperature transmitter of claim 13, and further comprising:

communication circuitry connected in communication between the microprocessor and a user interface.

17. The temperature transmitter of claim 13, wherein the microprocessor is connected in communication with a user interface and drives the user interface to display a correction factor determined by comparing the first temperature value to signals received from the second channel, and wherein the user interface signals the microprocessor to apply the correction factor in response to a user input.

18. The temperature transmitter of claim 13, wherein the microprocessor calibrates accuracy of the measurement programming by adjusting trim values at a plurality of temperature points.

19. The process control temperature transmitter of claim 13, and further comprising:

communication circuitry configured for communication over a 4-20 mA current loop.

20. The process control temperature transmitter of claim 13, and further comprising:

communication circuitry configured for communication via HART or Foundation Fieldbus communication protocol.