| 摘要 |
PURPOSE:To prevent the variance of a liquid concentration due to the fluctuation of a power source voltage to make the concentration detection width narrow, by converting a constant voltage to an AC to apply it to an electrode which detects the liquid concentration. CONSTITUTION:The concentration of a mixed liquid of a detergent supplied into a tub of an automatic tableware washing machine or the like is detected to control it to a prescribed concentration. A pair of electrodes P1 and P2 which detect this concentration are provided in the liquid, and the change of the electric resistance between both electrodes is detected to detect the concentration. A voltage is applied to both electrodes P1 and P2 for this detection; and an AC power source voltage e is transformed by a transformer 3 to obtain a DC constant voltage 4, and this voltage is converted to an AC by a DC/AC converting circuit 5, and this AC is used as the voltage applied to electrodes. The concentration detected by electrodes P1 and P2 is compared with a prescribed concentration of a reference voltage Vs by a comparing circuit 6; and when the concentration becomes lower, a transistor Q0 is turned on to operate a relay X. As the result, the detergent is supplied to control its concentration to a prescribed value. The application of the AC to electrodes P1 and P2 eliminates the generation of a harmful gas. |
