| 摘要 |
PURPOSE:To ensure safety operation of a boiler by switching to commercial power supply (C source) and giving a wind quantity control command, when the frequency variable power supply (V source) to a motor to drive fans for control of wind quantity of biler is in failure, and thereby suppressing change in wind pressure. CONSTITUTION:When the V power supply 5a to one of the fans 7a is in failure, a specific function signal is fed into that control input part 5b2 belonging to the other group to change the output frequency from the V power supply 5b so as to provide control of the wind quantity of the fan 7b, and the total wind quantity of the two fans can thus be stabilized. As this signal given to control input part 5b2, a signal with the effect to reduce the revolving speed of the V power supply 5b in the event of failure in the V power supply 5a may for ex. be given for a certain period of time, and then the value before failure occurrence in the V power supply 5a shall be restituted. This provides safety operation of the boiler continuously without requiring tripping of the boiler for switching the C power supply.
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