Temperature measurement and compensation in a fiber-optic sensor

• US 5,115,811 A
• Filed: 04/30/1990
• Issued: 05/26/1992
• Est. Priority Date: 04/30/1990
• Status: Expired due to Term

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Schweitzer, Jeffrey A., Seifert, George P., Hartlaub, Jerome T.
• Primary Examiner(s): Pellegrino, Stephen C.
• Assistant Examiner(s): SHUMAKER, STEVEN
• Application Number:
  US07/516,621
• Time in Patent Office: 757 Days
• Field of Search: 128/634, 128/636, 128/637, 128/736, 374/17-19, 374/141, 250/227.14, 250/227.18, 250/226, 356/412, 356/39-41
• US Class Current: 600/342
• CPC Class Codes: A61B 2560/0252 using ambient temperature
• CPC Class Codes: A61B 5/14539 for measuring pH
• CPC Class Codes: A61B 5/1459 invasive, e.g. introduced into the body by a catheter A61B5/1464 takes precedence
• CPC Class Codes: G01N 2021/3148 using three or more wavelengths
• CPC Class Codes: G01N 2021/3181 using LEDs
• CPC Class Codes: G01N 21/7703 using reagent-clad optical fibres or optical waveguides using measurement of total internal reflection or attenuated total reflection G01N21/552; optical fibres or waveguides per se G02B
• CPC Class Codes: G01N 21/80 Indicating pH value

Abstract

A fiber-optic sensor for measuring a parameter of a test fluid, including a chemical sensor, incorporating a dye composition which displays changes in its optical properties correlated to changes in the parameter to be measured. The sensor is coupled to an apparatus including a light source, and means for measuring light received from said sensor at three different peak wavelengths. The first wavelength is chosen such that the optical characteristics of the dye with respect to that wavelength do not change significantly with changes in the parameter to be measured. The second and third wavelengths are chosen such that optical characteristics of the dye with respect to these wavelengths do change along with changes in the parameter to be measured, and also change as a function of temperature. The light received from the sensor at first, second and third wavelengths is compared to determine the temperature of the test fluid and to provide a temperature correction for the parameter to be measured.

Claims

1. Apparatus for measuring a parameter of a test fluid comprising:

a catheter including a sensor incorporating a dye which displays changes in light absorption properties correlated to changes in the parameter to be measured and in correlation to changes in temperature;

means for applying first, second and third wavelengths of light to said sensor, said first wavelength chosen such that said absorptive characteristics of said sensor at said first wavelength do not change significantly with changes in said parameter to be measured, said second and third wavelengths chosen such that the absorptive characteristics of said sensor at both said second and third wavelengths do change in response to both changes in temperature and changes in said parameter to be measured; and

means for measuring light reflected from said sensor at said first, second and third wavelengths to provide a temperature corrected measurement of said parameter to be measured.

2. Apparatus according to claim 1 wherein the dye within said sensor is phenol red, and wherein said first and third wavelengths are approximately 440 nm and 570 nm, respectively.

3. An apparatus according to claim 1 or claim 2 wherein said parameter to be measured comprises pH or carbon dioxide concentration.

4. A method of measuring a parameter of a test fluid by using a fiberoptic sensor containing a dye which displays changes in light absorption properties correlated to changes in the parameter to be measured, comprising:

applying first, second and third wavelengths to said fiberoptic sensor while said sensor is in said test fluid, said first wavelength chosen such that absorptive characteristics of said dye at said first wavelength do not change significantly with changes in said parameter to be measured, said second and third wavelengths chosen such that the absorptive characteristics of said dye in said sensor at both said second and third wavelengths do change along with changes in both the parameter to be measured and with changes in temperature; and

measuring light reflected from said sensor at said first, second and third wavelengths and comparing said measurements to provide a temperature corrected measurement of said parameter to be measured.

5. A method according to claim 4, wherein said dye comprises a phenol red dye, and wherein said first, second and third wavelengths are approximately 830 nm, 440 nm, and 570 nm, respectively.

6. An apparatus for measuring a parameter of a test fluid, comprising:

a fiber-optic sensor including a dye which displays changes in optical properties correlated to changes in the parameter to be measured and in correlation to changes in temperature;

means for applying light to said sensor;

means for receiving light from said sensor, said means for applying and means for receiving together comprising means for measuring light received from said sensor at first, second and third wavelengths chosen such that said optical characteristics of said dye with respect to said first wavelength do not change significantly with changes in said parameter to be measured, said second and third wavelengths chosen such that said optical properties of said sensor at both said second and third wavelengths do change in both response to changes in temperature and changes in parameter to be measured; and

means responsive to said measurement of said light received from said sensor to provide a temperature corrected measurement of said parameter.

7. A method of measuring a parameter of a test fluid by employing a fiber-optic sensor containing a dye which displays changes in optical properties correlated to changes in the parameter to be measured and correlated to temperatures, comprising:

applying light to said sensor while said sensor is in said test fluid;

measuring light reflected from said sensor, said measurement comprising measuring the relative amounts of light received from said sensor at first, second and third wavelengths, said first wavelength chosen such that said optical properties of said dye at said first wavelength do not change significantly with changes in said parameter to be measured, said second and third wavelength chosen such that said optical properties of said dye in said sensor at both said second and third wavelengths do change along with both changes in the parameter to be measured and with changes in temperature; and

comparing said measurements to provide a temperature corrected measurement of said parameter.