| 摘要 |
PURPOSE:To provide a safety circuit which can detect the failure of a temperature detecting sensor, can immediately cut off a relay circuit and can stop supplies of hot- water and electricity to a floor panel, when the temperature detecting sensor consisting of a thermistor of negative characteristics fails, to a temperature controlling circuit in the floor heating device. CONSTITUTION:A floor temperature sensor 6 is connected to the base of a transistor Tr2 passing through a resistor R17 which is arranged in series with the sensor 6, and the emitter of said transistor is connected to the earth side, while the collector is connected to the anode side of a diode D1, as well as to be connected to one terminal of an electric power source circuit 14 passing through resistors R14 and R15. The cathode side of a diode D1 is connected to the inverted input terminal of a comparator OP2. The circuit is wired in such a manner that the current does not flow to the base and the emitter of a NPN transistor Tr2 when the floor temperature sensor 6 fails or a lead wire on the way is cut off. Accordingly, the voltage at the inverted input terminal of a comparator OP2 becomes higher than that at a non-inverted input terminal, and the output level from the comparator OP2 becomes low, and a relay Ry is turned OFF. As a result, heating to a heater 5 is stopped, at the same time, a signal to close a thermal valve 4 is outputted, and hot-water supply is stopped. |
