To provide an instrument for measuring water quality, in which a bad influence is not given to the measurement and which can prevent the contamination of a detecting face easily.
In an immersion-type turgidity meter which uses an optical system as a measuring means, a titanium dioxide film 1B2 is formed on its detecting face. A black light 3 is installed as an irradiation light source for the titanium dioxide film 1B2, and the whole face of the titanium dioxide film 1B2 at the front of a detecting window 1B is irradiated, via a condenser 4 and an optical fiber cable 2, with light whose main wavelength is near 360nm. A light-emitting diode 1C whose peak is in a near-infrared region is used for a light source at a measuring optical system, and photodiodes 1D whose peak is in a near-infrared region are used for a plurality of light-receiving elements surrounding the light-emitting diode 1C. Regarding the light-emitting diode 1C and the photodiodes 1D, their wavelength characteristic is selected in such a way that their wavelength region is owned jointly and that their light-emitting wavelength region is different from that of the black light 3.
SHIMIZU KOICHI
YOSHINO NORIMASA
