| 摘要 |
PURPOSE:To simplify circuit structure by a method wherein the output of a disconnection detecting circuit for an evaporating heater and hot water temperature detection is stopped for a predetermined time period by a single timer circuit. CONSTITUTION:When the temperature of water heated by a burner is extremely low, the output of a comparator 36 becomes ''1'' because the resistance value of a thermister 27 is very large. That is the output tells a disconnection though the operation is in normal conditions. Accordingly, it is unfavorable to drive an alarm circuit 2 at this timepoint. For this purpose, a transistor 22 is turned ON by the timer circuit 23 so that the output of the comparator 36, that is, the input of an exclusive circuit 40 becomes ''0''. After that, the water temperature is raised by the combustion during the operation of the timer circuit 23 and the output of the comparator 36 is inverted to ''0''. Accordingly, even if after the timeup of the timer circuit 23, the transistor 22 turns OFF to release the locking of input ''0'' state of the exclusive circuit 40, the alarm circuit 2 does not operate. |
