| 摘要 |
PROBLEM TO BE SOLVED: To provide a method and a device for detecting a failure of liquid level switches 6 or a liquid level meter 9, and a method and a device for detecting the liquid level, operating or stopping a pump 2 automatically, and thereby controlling surely the liquid level, even if the liquid level switches 6 or the liquid level meter 9 fail. SOLUTION: Each determination level by the liquid level switches 6 and the liquid level meter 9 is provided respectively on a plurality of spots having each different height in a liquid tank 100 so that each height is shifted mutually. When an actual liquid level detected by the liquid level meter 9 to a determination level by some liquid level meter is changed from a low position to a high position or from a high position to a low position, if a liquid level switch which is different from a naturally-supposed ON/OFF pattern of the liquid level switches exists, the liquid level switch is determined to be failed. COPYRIGHT: (C)2009,JPO&INPIT
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