| 摘要 |
PURPOSE:To prevent the malfunction due to foreign matters such as oil or the like by using a self-heating positive characteristics thermistor to detect a liquid level with a difference between heat radiation constants in water and in air. CONSTITUTION:When a positive characteristics thermistor 6 is placed in air, it is self-heated, and a current value is held down, and it is stabilized at a temperature determined by the heart radiation constant. In this state, since the inverted input - of a comparator 7 is lower than the noninverted input + which is a fixed reference potential, the output of the comparator 7 is in the high level. When the thermistor 6 is placed in water, the self-heating calorific value is held down because of a large heat radiation constant, and the output of the comparator 7 is inverted to become low-level. A microcomputer 8 receives the output of the comparator 7 and controls turning-on and off of a relay driving transistor 9 in accordance with a preliminarily determined control flow, and a drain pump is controlled by a drain pump controlling relay 10. |
