| 摘要 |
PROBLEM TO BE SOLVED: To supply a clean solution by allowing an electrical conductance sensor, that is used for controlling concentration, to also serve as a level sensor, and hence reducing the number of parts, reducing the cost, and simplifying the inside of a tank for facilitating cleaning. SOLUTION: A solution that fills the inside of an electrical conductance sensor 16 decreases linking with the water level of a dissolution tank 13 when feeding liquid, the inside of the electrical conductance sensor becomes empty and the area between electrodes 161 is insulated, the output change is utilized for substituting for a float switch, and the idling of a circulation pump 17 is prevented. Also, when the solution is to be stored in the dissolution tank 13 and a water level rises, the solution enters piping 132 making the area between insulted electrodes 131 conduct electricity, and the output change is utilized for substituting for the float switch, thus preventing overflow.
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