| 摘要 |
PURPOSE:To prevent any accident due to a malfunction in a relay switch from occurring by controlling a first relay switch, which performs an on-off changeover alone, for opening or closing, and also controlling a second relay switch for its changeover with output of a heater selector circuit. CONSTITUTION:One end of two heaters 3 and 4 is connected to a power source via a first relay switch in common use, while the other end of these two heaters 3 and 4 is connected to a transfer terminal of a single-pole, double tilt type second relay switch 11. And, this transfer terminal of the second relay switch 11 is connected to the power source, and these first and second relay switches 8 and 11 are made so as to be controlled for opening or closing by two relay drive circuits 14 and 15. Supposing that a contact piece of the first relay switch 8 to do troublesome on-off operations by temperature control has been deposited, these two heaters 3 and 4 are connected to the power source via the second single-pole double tilt type relay switch 11 to be controlled less in frequency by a heater selector circuit at the other end. With this constitution, not to mention that such an accident as these two heaters 3 and 4 are simultaneously energized is brought to nothing, such a possibility that the second relay switch 11 gets out of order due to deposition or the like becomes lessened.
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