Predictive temperature measurement system

• US 6,698,921 B2
• Filed: 03/14/2001
• Issued: 03/02/2004
• Est. Priority Date: 05/18/1999
• Status: Expired due to Term

• Current Assignee: Carefusion 303 Incorporated (Becton, Dickinson & Co)
• Original Assignee: ALARIS Medical Systems, Inc. (Becton, Dickinson & Co)
• Inventors: Siefert, Robert J.
• Primary Examiner(s): VERBITSKY, GAIL KAPLAN
• Application Number:
  US09/809,591
• Publication Number:
  US 20020003832A1
• Time in Patent Office: 1,084 Days
• Field of Search: 374/169, 374/102, 374/103, 374/104, 374/1, 374/2, 374/107, 374/208, 600/549, 600/484
• US Class Current: 374/169
• CPC Class Codes: G01K 7/42 Circuits effecting compensation of thermal inertia; Circuits for predicting the stationary value of a temperature

Abstract

A method and device for rapidly predicting the temperature of an object through a sensor reading of the object'"'"'s temperature by using a processor comprising finite impulse response (FIR) filters to determine the average value, the first derivative, and the second derivative of the sensed temperature based upon a predetermined number of temperature samples, apply a respective weighting factor to each of the average value, the first derivative, and the second derivative respectively, and calculate a temperature estimate by combining the weighted average value, the first derivative, and second derivative together with an offset factor.

Claims

1. A thermometer for measuring the temperature of an object, comprising:

a sensor which, when positioned to sense the temperature of the object, provides a time varying temperature signal in response to the temperature of the object;

a processor connected so as to sample the temperature signal a predetermined number of times, to determine the average value, the first derivative, and the second derivative of the temperature signal based upon the predetermined number of samples acquired, and to combine the average value, first derivative, and second derivative to calculate an estimate of the temperature of the object and provide an estimated final temperature signal; and

a display connected with the processor to receive and display the estimated final temperature signal.

2. The thermometer of claim 1 wherein the processor further applies a separate weighting factor to each of the average value, the first derivative, and the second derivative prior to combining the average value, the first derivative, and the second derivative to calculate the temperature estimate.

3. The thermometer of claim 2 wherein the predetermined number of samples are acquired over a predetermined time frame.

4. The thermometer of claim 3 wherein the processor samples the temperature signal around twenty-one times over a time frame of approximately two seconds to determine the average value, the first derivative, and the second derivative of the signal.

5. The thermometer of claim 3 wherein the processor continuously samples the signal after acquiring an initial predetermined number of samples and continuously recalculates the temperature estimate based on the last selected number of samples acquired as each new sample is acquired.

6. The thermometer of claim 5 wherein the thermometer displays on the display a final temperature estimate calculated by the processor after the sensor has been in contact with the object for a predetermined length of time.

7. The thermometer of claim 5 wherein the thermometer displays on the display a final temperature estimate calculated by the processor only if the last value of the first derivative calculated by the processor lies in a predetermined range of values.

8. The thermometer of claim 5 wherein the thermometer displays on the display a final temperature estimate calculated by the processor only if the last value of the second derivative calculated by the processor lies in a predetermined range of values.

9. The thermometer of claim 5 wherein the final temperature estimate displayed by the thermometer is equal to the average of a selected number of the temperature estimates calculated by the processor.

10. The thermometer of claim 5 wherein the thermometer displays on the display a final temperature estimate only if the maximum difference between any two of a predetermined number of last temperature estimates calculated by the processor is less than a predetermined value.

11. A thermometer for measuring the temperature of a biological subject comprising;

a sensor which, when positioned to sense the temperature of the subject, provides a time varying temperature signal in response to the temperature of the subject;

a processor comprising a finite impulse response filter connected so as to sample the temperature signal a selected number of times, to determine an average value, a first derivative, and a second derivative of the temperature signal based upon the selected number of samples acquired, the processor also configured to combine the average value, first derivative, and second derivative to calculate an estimate of the temperature of the subject and provide an estimated final temperature signal;

wherein the processor recalculates the temperature estimate based on a selected number of new samples acquired by the processor later in time, thereby generating a plurality of temperature estimates; and

a display connected with the processor to receive and display the display the estimated final temperature signal only if the difference between any two of a selected number of the temperature estimates calculated by the processor is less than a predetermined value.

12. The thermometer of claim 11 wherein the thermometer displays on the display a final temperature estimate calculated by the processor after the sensor has been in contact with the subject for a predetermined length of time.

13. The thermometer of claim 11 wherein the thermometer displays on the display a final temperature estimate calculated by the processor only if the last value of the first derivative calculated by the processor lies in a predetermined range of values.

14. The thermometer of claim 11 wherein the thermometer displays on the display a final temperature estimate calculated by the processor only if the last value of the second derivative calculated by the processor lies in a predetermined range of values.

15. The thermometer of claim 11 wherein the final temperature estimate displayed by the thermometer is equal to the average of a selected number of the temperature estimates calculated by the processor.

16. The thermometer of claim 11 wherein the processor further adds an ambient temperature offset coefficient to the sum of the weighted average value, first derivative, and second derivative to calculate the temperature estimate.

17. The thermometer of claim 16 wherein:

the sensor further provides an initial signal corresponding to the ambient temperature; and

the process further determines the square of the ambient temperature, applies a separate weighting factor to each of the ambient temperature and the square of the ambient temperature, and combines the weighted value of the ambient temperature with the weighted square of the value of the ambient temperature to calculate the ambient temperature offset coefficient.