PURPOSE: To enable adaption to electric characteristics of city water as water for a tank and eliminate malfunction of a signal by driving a feed water pump at a water-shortage-time feed water level or water feeding start water level and stopping the feed water pump at a water feeding stop water level.
CONSTITUTION: A power circuit 2 supplies electric power to respective oscillation, detection, and control circuits 3, 4, and 5, the oscillation circuit 3 oscillates high frequency pulses of 1300Hz, and the frequency pulse voltage is applied between a reference electrode EE and water level electrodes E1, E2, and E3 fitted to the water tank 1, The detection circuit detects a signal current and decides only a signal frequency component. In this case, it is discriminated by a band-pass filter amplifier which is set to a fundamental frequency fc=1300Hz, and a comparator surely discriminates it to detect high frequency signals from E1, E2, and E3. Namely, the feed water pump is driven at the water-shortage-time feed water level or water feeding start water level and stopped at the water feeding stop water level.
FUKUDA TAKEHIKO
FUJITA TAKUSHI
