Determination of the alcohol content of blood

Abstract

A relationship exists between the concentration of ethanol in human breath and blood. Ethanol absorbs infrared energy in the region of 3.46 mu. In this method the concentration of ethanol in breath is measured by collecting a sample in a chamber and passing through it a filtered, directional, and interrupted beam of infra-red energy at 3.46 mu. The path length is fixed. The exit energy falls on a tuned radiant energy detector. This beam is compared with a similar beam of radiant energy not capable of being absorbed by ethanol. The two signals are fed into a differential amplifier which activates a servo-system that moves a tapered radiant-energy absorbing medium in the path of one of the energy beams until a null condition is achieved. The distance the tapered medium must be moved to establish the null condition is measured by a potentiometer operably associated with it. The potentiometer provides a signal that can be displayed by an analog or digital device calibrated directly in units of blood or breath ethanol concentration.

We claim: 
     
       1. An arrangement for determining the alcohol content of blood by measuring the concentration of alcohol in exhaled breath, comprising a measuring chamber, an inlet on the measuring chamber by which exhaled breath can be blown in, a radiation inlet at one end of the measuring chamber and a radiation outlet at the other end of the measuring chamber, a radiation source in the form of a wide band thermal radiator located upstream of the radiation inlet, an interrupting device in the path of the beam, a filter having a pass band at 3.46 μm arranged as a tuned receiver downstream of the radiation outlet of the measuring chamber, a first photoelectric detector arranged beyond the filter, a second detector arranged in the path of the beam beyond the radiation outlet of the measuring chamber and in front of the filter, an amplifier connected to the output of the first detector, reference voltage source connected to the output of the second detector, a differential amplifier connected to both the output of the amplifier and the output of the reference voltage source, a drive motor connected to the output of the differential amplifier, an absorption device which is displaceable in and at right angles to the path of the beam between the radiation outlet of the measuring chamber and the photo-electric detector, the absorption device being in the form of a wedge connected to the drive motor and having absorption in the band width of the filter, the drive motor being adapted to automatically displace the wedge to maintain at zero the voltage at the output of the differential amplifier and an indicator which is connected to the drive motor for the wedge and arranged to indicate the position of the wedge in the path of the beam. 
     
     
       2. An arrangement according to claim 1, having a second filter which is exchangeable for said first mentioned filter, the second filter having a pass band in the range of the absorption bands of acetone. 
     
     
       3. An arrangement according to claim 1, in which the second detector is arranged in the region of reflection of the filter and receives unfiltered radiation reflected from the front of the filter. 
     
     
       4. An arrangement according to claim 3, in which the interrupting device comprises a rotatable vane and a drive motor therefor and in which the output signal of the second detector additionally acts as a control variable for regulating the rotational speed of the interrupting device. 
     
     
       5. An arrangement according to claim 4, further comprising a device which is connected to the output of the second detector and which compares the frequency produced by the interrupting device with a reference value and feeds a regulating voltage, dependent upon this comparison, to the drive motor of the interrupting device. .Iadd. 6. A device for measuring the concentrations of ethanol and acetone in a sample of human breath, said device comprising, in combination, a. an infrared radiation source;   b. a measuring chamber adapted to contain a sample of human breath, said radiation from said source, directed through said chamber;   c. a first filter having a pass band at a predetermined first wavelength;   d. a second filter having a pass band at a predetermined second wavelength, said first and second wavelengths chosen such as to have band passes at different ranges of absorption for ethanol and acetones, said filters disposed for insertion in the path of said radiation after passing through said chambers;   e. detector means for measuring the radiation which has passed said filters; and   f. means for converting the output of said detector means into signals which are proportional to the concentrations of ethanol and acetone in said breath sample. .Iaddend..Iadd. 7. The device of claim 6 wherein said first wavelength is one corresponding to a high degree of absorption by ethanol, said wave length also being one of absorption by acetones and said second wavelength is one at which there is a high degree of absorption by acetones. .Iaddend..Iadd. 8. The device of claim 6 wherein said first wave length is 3.46 μm. .Iaddend. .Iadd. 9. In apparatus for determining the alcohol content of blood by measuring the concentration of alcohol in exhaled breath, said apparatus including an infrared radiation source; a measuring chamber through which said radiation is directed; a first filter having a bandpass selected to be in the range of infrared absorption by ethanol; detector means for detecting the amount of radiation passing through said measuring chamber and first filter, and means to convert the output of said detector means into a signal proportional to concentration, a method of detecting the falsification of a reading because of acetones in the blood comprising:   (a) providing a second filter which exhibits a bandpass in the range of high infrared absorption by acetones; and   (b) determining the degree of absorption and resulting concentrations with each of the filters inserted between the measuring chamber and detector means, where by the effect on the concentration obtained with the first filter of any acetones in the blood can be determined. .Iaddend.