| 摘要 |
<p>A method and apparatus for determining the concentration of a predetermined energy absorbing compound in a breath sample even in the presence of other unknown energy absorbing compounds. Infrared energy of three wavelengths is passed through the collected sample. The first wavelength of infrared energy, 3.95 microns for example, is selected to be insensitive to absorption by both the predetermined energy absorbing compound such as ethanol and the unknown energy absorbing compounds such as acetone and water vapor. The second wavelength of infrared energy, 3.48 microns for example, is selected to be significantly absorbed by ethanol. The third wavelength of infrared energy, 3.39 microns for example, is selected to be significantly absorbed by acetone and water vapor. Operational amplifiers (74, 76, 78) responsive to the first, second and third predetermined wavelengths of energy are utilized to subtract the effect of the absorption by acetone and water vapor so as to generate an electrical output signal (118) which is proportional only to the ethanol concentration.</p> |
