| 摘要 |
PURPOSE:To disconnect a load when a contact is welded, by a method wherein the luminous part of a photo coupler is connected parallel to an evaporating heater, the outputs of a photo collector and a burner temperature control circuit are connected to the input of an Ex-OR circuit, and the output thereof is connected to the input of a safety circuit. CONSTITUTION:With a contact 15a welded, a current continuously flows to an evaporating heater 3 and a luminous part 29a of a photo coupler. The photo transistor of a collector part 29b is also left in an electrical connection state, and the single-sided input of an Ex-OR circuit 31 is left in a ''1'' state. The other input is brought to ''0'' when the temperature of a burner is increased to a given value, and thereby an output is inverted and brought to a ''1'' state. Thus, a signal is supplied to a safety circuit 25, and a relay 26 and a contact 26a are brought into an exciting state and an opening state, respectively to stop energization. simultaneously, a signal is supplied to also an OR circuit 22 and a transistor 20, and operation of a combustion control circuit 23 and a relay driving part 14 is also stopped. This enables to effect disconnection within an ordinary burner control temperature range even when a contact is welded, and permits prevention of an abnormal increase in temperature. |
