METHOD AND APPARATUS FOR MEASUREMENT OF CONCENTRATION OF LIQUID

PROBLEM TO BE SOLVED: To reduce the measuring error of the concentration of a liquid, to be measured, due to an irregularity in the characteristic of a light-emitting body by a method wherein, before the concentration of the liquid to be measured is measured, the electrifying current of the light-emitting body is calibrated to be a proper value and the wavelength of light emitted from the light-emitting body is calibrated. SOLUTION: In a liquid-concentration measuring apparatus, the concentration of a liquid to be measured is measured. In the measuring apparatus, a computing means computes a concentration corresponding value on the basis of the output of a light-receiving body 12A which receives transmitted light obtained when light is transmitted through a translucent reference substance whose concentration corresponding value is known. An adjusting means is composed of a comparison means by which the known concentration corresponding value is compared with the concentration corresponding value computed by the computing means and of a current adjusting means by which the electrifying current of a light-emitting body 11A is adjusted according to the difference between both. A current increasing means which increases the electrifying current of the light-emitting body 11A, a current decreasing means which decreases the electrifying current and a current setting means by which the electrifying current is stored and fixed when the measured concentration is equal to the know concentration corresponding value are contained in the current adjusting means. That is to say, the adjusting means adjusts an electrifying amount to the light-emitting body 11A so as to adjust the wavelength of emitted light.