THERMOMETER CALIBRATION

• US 20090154519A1
• Filed: 02/19/2009
• Published: 06/18/2009
• Est. Priority Date: 05/19/2006
• Status: Active Grant

• Current Assignee: Cardinal Health Ireland Unlimited Company (Cardinal Health, Inc.)
• Original Assignee: Sherwood Services AG
• Inventors: Price, Jeffrey E.
• Granted Patent: US 7,731,418 B2
• Time in Patent Office: Days
• US Class Current: 374/1
• CPC Class Codes: G01J 5/16 Arrangements with respect to the cold junction; Compensating influence of ambient temperature or other variables
• CPC Class Codes: G01J 5/53 Reference sources, e.g. standard lamps; Black bodies
• CPC Class Codes: G01J 5/80 Calibration using comparison with reference sources G01J5/52
• CPC Class Codes: G01K 15/00 Testing or calibrating of thermometers

Abstract

A method for calibrating a thermometer is provided. The method includes deriving values of at least two different reference calibration coefficients of a reference calibration equation. The reference calibration equation relates temperature of a reference temperature sensor to at least two different calibration coefficients and a measured characteristic of the reference temperature sensor. A primary temperature sensor of the thermometer is calibrated using the derived values of the at least two different reference calibration coefficients. In another method for calibrating a thermometer, value of at least one reference calibration coefficient is derived from a reference calibration equation. The reference calibration equation is a non-linear equation relating the temperature of the reference temperature sensor to the at least one calibration coefficient and a measured characteristic of the reference temperature sensor.

Claims

1. A method for calibrating a thermometer, said thermometer comprising a primary temperature sensor and a reference temperature sensor, said reference temperature sensor being positioned proximate to the primary temperature sensor and being responsive to an extraneous temperature affecting the primary temperature sensor, said method comprising:

calibrating the reference temperature sensor, including

controlling the temperature of the reference temperature sensor to a first temperature value,

measuring a characteristic of the reference temperature sensor at said first temperature value,

controlling the temperature of the reference temperature sensor to a second temperature value different than the first temperature value,

measuring a characteristic of the reference temperature sensor at said second temperature value,

deriving values of at least two different reference calibration coefficients of a reference calibration equation, the reference calibration equation relating the temperature of the reference temperature sensor to said at least two different calibration coefficients and the measured characteristic of the reference temperature sensor,

storing the derived values of said at least two different reference calibration coefficients to a memory of the thermometer; and

calibrating the primary temperature sensor using said derived values of said at least two different reference calibration coefficients.

2. A method as set forth in claim 1 wherein said calibrating the reference temperature sensor further includes

controlling the temperature of the reference temperature sensor to a third temperature value different than the first and second temperature values,

measuring a characteristic of the reference temperature sensor at said third temperature value,

wherein said at least two different reference calibration coefficients comprises at least three different reference calibration coefficients.

3. A method as set forth in claim 2 wherein said reference calibration equation is a non-linear equation.

4. A method as set forth in claim 3 wherein said reference calibration equation is the following equation:

$T_s=a+\frac{b}{R}+\frac{c}{R^2}$

where Ts is the temperature of the reference temperature sensor,

R is the measured characteristic of the reference temperature sensor, and

a, b, and c are the calibration coefficients of the reference temperature sensor calculated based upon the first, second and third temperature values and the corresponding measured characteristics.

5. A method as set forth in claim 4 wherein the reference temperature sensor comprises a temperature-dependent resistor and the primary temperature sensor comprises a thermopile.

6. A method as set forth in claim 1 wherein said calibrating the primary temperature sensor comprises:

exposing the primary temperature sensor to a first radiation source at a predetermined first source temperature value;

measuring the output voltage of the primary temperature sensor during exposure of the primary temperature sensor to the first radiation source;

measuring the characteristic of the reference temperature sensor during exposure of the primary temperature sensor to the first radiation source;

repeating the exposing and both measurings for at least one other radiation source emitting a different amount of radiation at a predetermined temperature value different than the first radiation source; and

utilizing the measured output voltages, the measured characteristics of the reference temperature sensor, and the predetermined temperature values of the radiation sources to solve a second calibration equation, said second calibration equation relating measured output voltage of the primary temperature sensor, measured characteristic of the reference temperature sensor, and the predetermined temperature values of the radiation sources for use in calibrating the primary temperature sensor.

7. A method for calibrating a thermometer, said thermometer comprising a primary temperature sensor and a reference temperature sensor, said reference temperature sensor being positioned proximate to the primary temperature sensor and being responsive to an extraneous temperature affecting the primary temperature sensor, said method comprising:

calibrating the reference temperature sensor, including

controlling the temperature of the reference temperature sensor to a first temperature value,

measuring a characteristic of the reference temperature sensor at said first temperature value,

deriving value of at least one reference calibration coefficient of a reference calibration equation, the reference calibration equation being a non-linear equation relating the temperature of the reference temperature sensor to said at least one calibration coefficient and the measured characteristic of the reference temperature sensor,

storing the derived value of said at least one reference calibration coefficient to a memory of the thermometer, and

calibrating the primary temperature sensor using said derived value of said at least one reference calibration coefficient in said non-linear reference calibration equation.

8. A method as set forth in claim 7 wherein the reference calibration equation is a rational equation.

9. A method as set forth in claim 8 wherein said calibrating the reference temperature sensor further includes

controlling the temperature of the reference temperature sensor to a second temperature value different than the first temperature value, and

measuring a characteristic of the reference temperature sensor at said second temperature value,

wherein said at least one reference calibration coefficient comprises at least two reference calibration coefficients.

10. A method as set forth in claim 9 wherein said calibrating the reference temperature sensor further includes

controlling the temperature of the reference temperature sensor to a third temperature value different than the first and second temperature values,

measuring a characteristic of the reference temperature sensor at said third temperature value,

wherein said at least two different reference calibration coefficients comprises at least three different reference calibration coefficients.

11. A method as set forth in claim 10 wherein said reference calibration equation is the following equation:

$T_s=a+\frac{b}{R}+\frac{c}{R^2}$

where Ts is the temperature of the reference temperature sensor,

R is the measured characteristic of the reference temperature sensor, and

a, b, and c are the calibration coefficients of the reference temperature sensor calculated based upon the first, second and third temperature values and the corresponding measured characteristics.