| 摘要 |
PROBLEM TO BE SOLVED: To make calculable the quantity of an ultraviolet ray absorbing substance by measuring the frequency and the time change rate before housing a water to be measured, measuring the frequency after housing after a specific time, and correcting either of frequencies to a value after housing by the time change rate. SOLUTION: The light containing a short wave length ultraviolet ray is projected to a photoelectric tube 11 from an ultraviolet ray emitting light source 4 to generate a pulse-like current by discharge to periodically output pulse voltage signals from a converting circuit 19c. A frequency measuring means 27 calculates frequencies by counting the pulse voltage signals in a prescribed time, and by repeating this a prescribed number of times, an average value of the frequencies and a frequency time change rate are calculated by a calculating means 28 to be stored. A solenoid valve 24 is opened, and measuring object water 2 is introduced into an underwater dissolved substance detector so that a short wave length ultraviolet ray is partially absorbed in an ultraviolet ray absorbing substance in it. After a prescribed time after the introduction, similar operation is repeated to recalculate a frequency average value. The calculating means 28 corrects a characteristic change by discharge of the photoelectric tube 11 on the basis of an average frequency, and calculates the concentration to be displayed on a display part 26.
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