PURPOSE: To keep the concn. of the low conc. salt water in a first tank constant, in supplying water to the first tank and intermittently supplying high concn. salt water to the first tank from a second tank by a specific quantity at the same time, by calculating the supply number of times of high concn. salt water using the previous water supply time and calculating an intermittent supply time interval.
CONSTITUTION: When the water level in a first tank 21 is changed to a lower limit water level by the utilization of the low conc. salt water in the first tank 21, water such as tap water is supplied to the first tank 21 from an external water supply source 10B until the water level in the tank 21 becomes an upper water level and, at the same time, high conc. salt water is intermittently supplied to the tank 21 by a specific quantity from a second tank 24. At that time, the previous water supply time is stored and, by the use of this water supply time, the supply number of times of the high conc. salt water to the tank 21 from the tank 24 during the water supply time is calculated and the time interval supplying the high conc. salt water intermittently is calculated. Since the water supply state from an external water supply source 10B is not suddenly changed in usual, the concn. of the salt water in the tank 21 is kept almost constant.
KAMIYA YOSHINORI
TSUCHIKAWA KOJI
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