Calibration of process control temperature transmitter

• US 5,829,876 A
• Filed: 05/16/1997
• Issued: 11/03/1998
• Est. Priority Date: 09/27/1994
• Status: Expired due to Term

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Kirkpatrick, William R., Schwartz, Bradley N.
• Primary Examiner(s): Biegel, Ronald L.
• Assistant Examiner(s): AMROZOWICZ, PAUL DOUGLAS
• Application Number:
  US08/857,236
• Time in Patent Office: 536 Days
• Field of Search: 374/1, 374/179, 374/180, 374/181, 374/182, 374/183, 364/557, 364/571.01, 364/574
• US Class Current: 374/1
• CPC Class Codes: G01K 15/00 Testing or calibrating of thermometers
• CPC Class Codes: G01K 7/13 Circuits for cold-junction compensation
• CPC Class Codes: G01K 7/20 in a specially-adapted circuit, e.g. bridge circuit

Abstract

A transmitter in a process control loop measures temperature. A calibrator includes a known calibration element which is connected to the transmitter. Software in the transmitter compares a measured value of the calibration element with the actual value of the calibration element and responsively calibrates the transmitter. The calibrator includes a temperature calibration sensor for coupling to a terminal block of the transmitter. The temperature calibration sensor provides an actual temperature input to the transmitter. The transmitter measures actual temperature of the terminal block and compares actual temperature with a temperature measured by an internal terminal block temperature sensor, and responsively calibrates the internal temperature sensor.

Claims

1. A calibrator for calibrating a temperature transmitter in a process control loop, comprising:

a NIST traceable reference;

a plurality of electrical connectors adapted for electrically connecting to a terminal block of the transmitter;

circuitry for coupling to the process control loop and transmitting values of the NIST traceable reference to the transmitter; and

a switch connected for selectively coupling the NIST traceable reference to the plurality of electrical connectors.

2. The calibrator of claim 1 wherein the NIST traceable reference is a NIST traceable resistance.

3. The calibrator of claim 1 wherein the NIST traceable reference is a NIST traceable voltage.

4. The calibrator of claim 1 wherein the NIST traceable reference is a temperature probe.

5. The calibrator of claim 1 including a NIST traceable temperature probe adapter coupling to the terminal block and measuring a cold junction temperature.

6. A method of calibrating a temperature transmitter in a process control loop, comprising:

connecting an input of the transmitter to a NIST traceable reference;

transmitting the value of the NIST traceable reference to the transmitter;

comparing the communicated value of the NIST traceable reference with a measured value of the NIST traceable reference; and

responsively calibrating the temperature transmitter based upon the comparison.

7. The method of claim 6 wherein the step of transmitting comprises transmitting information over the process control loop to the transmitter.

8. The method of claim 6 including transmitting the communicated value of the NIST traceable reference prior to calibrating and transmitting the measured value of the NIST traceable reference after calibration.

9. The method of claim 6 including:

measuring temperature of a terminal block of the transmitter;

communicating the measured temperature to the transmitter;

comparing communicated temperature with an internally measured terminal block temperature; and

calibrating the transmitter based upon the comparison.

10. The method of claim 6 wherein the NIST traceable reference is a resistance.

11. The method of claim 6 wherein the NIST traceable reference is a voltage.

12. The method of claim 6 wherein the NIST traceable reference is a temperature probe.