| 摘要 |
PROBLEM TO BE SOLVED: To sense a fault occurring in an amplifying means by providing a varying circuit in an input unit of the means, and judging the fault from a change of an output signal occurring when operated. SOLUTION: A thermoelectromotive force of a thermocouple 2 due to a flame of a gas burner B is amplified by an operational amplifier 3, an ignition of the burner B is sensed by a controller 1, and a safety valve SV on the way of a gas tube GP is opened and held. When the burner B is flame-failed, the flame failure is judged due to a decrease of the force of the thermocouple 2, and the valve SV is closed. If the thermocouple 2 is disconnected, an output signal of the amplifier 3 always monitored by the controller 1 becomes a not normal value, and the controller 1 judges the disconnection of the thermocouple 2. Here, a transistor 4 for short-circuiting a connecting resistor 31 of a terminal 3b of the amplifier 3 is provided, periodically closed by the controller 1 to short-circuit the resistor 31. Then, if the amplifier 3 is normal, its output signal is changed in a predetermined width, but if the amplifier 3 is faulted, its output signal is not changed in its predetermined width, and hence the amplifier is judged as a fault.
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