COMPUTING TYPE OPTICAL ABSORPTION MIXTURE ANALYZER

• US 3,825,342 A
• Filed: 05/08/1972
• Issued: 07/23/1974
• Est. Priority Date: 05/07/1971
• Status: Expired due to Term

• Current Assignee: Dieter Piroth, Dietrich Werner Lubbers, Reinhard Wodick
• Original Assignee: Dieter Piroth, Dietrich Werner Lubbers, Reinhard Wodick
• Inventors: Lubbers, Dietrich Werner, Wodick, Reinhard, Piroth, Dieter
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): Clark, Conrad
• Application Number:
  US05/251,538
• Time in Patent Office: 806 Days
• Field of Search: 356/39,40,41,179,186,205,206,180,184
• US Class Current: 356/41
• CPC Class Codes: G01N 21/314 with comparison of measurements at specific and non-specific wavelengths dual wavelength spectrometry G01J3/427

Abstract

The proportional concentration of a given substance in a mixture of substances, e.g. the specific oxyhaemoglobin content of blood, is determined by an apparatus which measures the absorption, by the mixture, of electromagnetic radiation, as light, at three specific wavelength and calculates and indicates the desired concentration.

Claims

1. Apparatus for determining the proportional concentration of a given component in a mixture of substances by measuring the absorption of different wavelengths of a light beam by the mixture of substances, comprising a light source which supplies a beam incident upon the mixture of substances, chromatic beam splitter means for separating the beam in which the spectral distribution of energy has been changed by the mixture (object beam) inTo at least three largely monochromatic spectral fractions grouped respectively about a corresponding number of selected wavelengths ( lambda 1, lambda 2, lambda 3 . . . ), photoelectric transducer means for converting three of said different spectral fractions into corresponding electrical signals (S1, S2, S3), and electronic circuitry means for processing the electrical signals into an output signal corresponding to the wanted concentration, characterised in that the electronic processing circuitry derives an output signal (g) from said three electrical signals (S1, S2, S3), according to the following function g (a Delta 2 - b Delta 1)/((a - u) Delta 2 + (v - b) Delta 1) wherein a, b, u and v are constants for the measurement relating to said given component and two of the three wavelengths, Delta 1 is the difference (S1 - S2) between the electrical signals representing the spectral fractions respectively of a first and second of said three wavelengths ( lambda 1, lambda 2) and Delta 2 is the difference (S3 - S2) between the electrical signals representing the spectral fractions respectively of the third and one of the other two of said wavelengths ( lambda 3, lambda 2).

2. Apparatus as claimed in claim 1 in which the wavelengths lambda 1, lambda 2, lambda 3, into which the chromatic beam splitter separates the object beam, are so chosen that the extinction due to the concentration of the wanted component varies as much as possible, whereas the extinction due to other components of the substance mixture remains substantially constant during the measurement.

3. Apparatus as claimed in claim 1 for measuring the degree of oxygenation of blood, in which the constants a, b, u and v satisfy the equations:

a epsilon d ( lambda

     1) - epsilon d ( lambda

     2) b epsilon d ( lambda

     3) - epsilon d ( lambda

     2) u epsilon o ( lambda

     1) - epsilon o ( lambda

     2) v epsilon o ( lambda

     3) - epsilon o ( lambda

     2) where epsilon d and epsilon o are respectively the molar coefficients of extinction of oxygenated and deoxygenated haemoglobin at the wavelengths shown in brackets.

4. Apparatus as claimed in claim 3 in which each of the constants a, b, u and v is much less than 1/cd, where c is the total concentration of the haemoglobin and d is the thickness of a layer in which absorption has taken place.

5. Apparatus according to claim 3, for measuring the degree of oxygenation of blood, characterised in that lambda 1 530 nm lambda 2 538 nm lambda 3 550 nm

6. Apparatus as claimed in claim 1, in which the electronic processing circuitry means contains two first difference circuits to which the electrical signals corresponding respectively to the first and second and to the third and second spectral fractions are applied, and which supply output signals ( Delta 1, Delta 2) representing the differences between the said input signals;

the outputs of the difference circuits are connected respectively to the inputs of two second difference circuits which supply further difference signals representing the differences between signals proportional to the first above difference signals ( Delta 1 and Delta

     2), and that the outputs of the latter difference circuits are connected to the inputs of a dividing circuit which produces an output signal representing the concentration g of the wanted component.

7. Apparatus as claimed in claim 6, in which the beam splitter comprises a rotating filter plate, the electronic processing circuitry contains a switch for sequentially separating the electrical signals corresponding to the different Spectral fractions, and integrating circuits are respectively interposed between the switch and said two first difference circuits.

8. Apparatus as claimed in claim 7, in which the outputs of the two first difference circuits are connected respectively to the inputs of the third and fourth difference circuits through circuits providing adjustable signal transfer ratios.

9. Apparatus as claimed in claim 1, in which the chromatic beam splitter provides three additional spectral fractions of the object beam, and the photoelectric transducer supplies three additional electrical signals (S4, S5, S6) on a time sharing basis with respect to the aforesaid electrical signals (S1, S2, S3) to the first two difference circuits and in which, further, there is provided additional electronic processing circuitry means to the input of which the output of said first two difference circuits is provided on said time sharing basis, said additional electronic processing circuitry means containing a second dividing circuit of which one input is connected as aforesaid to the output of the first difference circuit and the second input is connectable via a sign reversing circuit as aforesaid to the output of the second difference circuit, and containing also a logarithm-forming circuit the input of which is connected to the output of said second dividing circuit.