Optical density detector

Abstract

An optical density detector which comprises a first light source for emitting a first light which belongs to a wavelength region in which the first light is hardly absorbed by a specific material contained in a sample, a second light source for emitting a second light which belongs to a wavelength region in which the second light is absorbed, substantially as compared with the first light, by the specific material, wherein a peak-wavelength of the second light is shifted by change of a temperature and change of an absorption of the specific material caused by the peak-wavelength shift is characteristic of a linear equation with a gentle grade, light receiving device for measuring a quantity of the first and the second lights which are transmitted through the sample, an arithmetic unit for calculating difference of absorbance between the first light and the second light of which both change depending on the density of the specific material, a temperature measuring device for measuring the temperature of the first and the second light sources and the light receiving device, or measuring the ambient temperature around the first and the second light sources and the light receiving device and compensation unit for compensating the difference of absorbance which is calculated by the arithmetic unit, with the absorption coefficient of the specific material at a shifted peak-wavelength of the second light, wherein the shifted peak-wavelength is calculated on the basis of a measured value measured by said temperature measuring device.