To extend the life of a light source and to reduce the frequency of maintenance by using a GaN blue light emitting diode increased in luminous intensity in the vicinity of the specific wavelength of a liquid to be measured as a light source.
A GaN blue light emitting diode 2 driven on the basis of the continuous pulse voltage of voltage of 5.1μs by a pulse generating circuit 1 is used as a light source and laser beam is discharged through a pinhole 3. BPF 4 of a center wavelength of 385nm cuts the broad spectrum with a peak wavelength of 450nm to divide this laser beam by a half mirror 6. Irradiation beam measuring laser beam is transmitted by a photoelectric conversion element 9a so that transmitted laser beam passes through a cell 7 with a light path length of 10mm and a liquid 8 to be measured and converted to electric signals by a photoelectric converter 9b. An operation circuit 10 performs the logarithmic operation of a ratio of both electric signals and, from this value, the logarithmic ratio operation value when an already measured liquid 8 is pure water is subtracted and a calibrated value is set to absorbancy in the vicinity of a wavelength of 385μm. Therefore, the life of a light source becomes long and frequency of maintenance can be reduced.
OODO TOKIO
MATSUYAMA HIDEAKI
IKOMA MASAKAZU
