Method and apparatus for measuring absorption coefficient of a medium
The present invention discloses a method to optically measure the absorption coefficient of a liquid or gas medium, without affecting the medium. Such absorption spectrum can be utilized to quantify the chemical components of the medium, or other metrics such as color or signature of the medium. The method acknowledges the possible drifts in the optical components of the system with time and measures the absorption coefficient independently of the state of the optical components. Therefore, there is no need to calibrate the system or take reference measurements. The method presented can be implemented cost effectively, designed in compact systems, and is energy efficient, thus, meeting the stringent challenges of spaced constrained remote systems such as aging wine barrels.
1 . A method of measuring an absorption coefficient of a medium across a light spectrum of wavelengths, the method comprising:
setting a first optical path length L 1 as the total length a specific light traverses the medium;
for L 1 , measuring a first light output intensity I 0_1 for each wavelength of interest across a spectrum of said specific light that traverses the medium for length L 1 , thereby creating a first I 0_1 data set;
setting a second optical path length L 2 as the total length the specific light traverses the medium;
for L 2 , measuring a second light output intensity I 0_2 for each wavelength of interest across the spectrum of said specific light that traverses the medium for length L 2 , thereby creating a second I 0_2 data set;
calculating the natural log for each I 0 from the first I 0_1 data set corresponding to length L 1 , thereby creating a third data set;
calculating the natural log for each I 0 from the second I 0_2 data set corresponding to length L 2 , thereby creating a fourth data set; and
fitting data from the third data set for each wavelength and data from the fourth data set for each wavelength to a linear function line of the natural log of a light intensity versus length, L, wherein a slope of the linear function line indicates the absorption coefficient of the medium and an intercept point where the linear function line intercepts a vertical axis conveys data relating to one or more variables, wherein the one or more variables are independent of absorption coefficient measurement.
2 . A method as recited in claim 1 wherein an offset in length L 1 or L 2 is independent of arriving at an accurate measurement of the absorption coefficient.
3 . A method as recited in claim 1 further comprising:
tracking variables in a set of variables to obtain a maintenance status of the optical sensor.
4 . A method as recited in claim 1 wherein a light source emits the specific light has a plurality of wavelengths and is used to measure other chemicals in the medium.
5 . A method as recited in claim 1 wherein the absorption coefficient is determined from the slope of the linear function line representing a linear relationship between the natural log of the light intensity and the length, L.
6 . A method as recited in claim 1 wherein the medium is one of a gas, a liquid, wine, whiskey, or other alcohol.
7 . A method as recited in claim 1 further comprising:
setting a third optical path length L 3 being the third total length the specific light traverses the medium; and
for L 3 , measuring a third light output intensity I 0_3 for each wavelength of interest across a spectrum of said specific light that traverses the medium for length L 3 , thereby creating a third I 0_3 data set.
8 . A method as recited in claim 1 wherein a set of variables includes an input light intensity, I i , a first transmission time T 1 , a second transmission time T 2 and a responsivity, R, of a photo detector in an optical sensor.
9 . A method as recited in claim 8 wherein one or more variables in the set of variables require calibration.