| 摘要 |
PURPOSE:To start and finish efficiently extracting sludge in a settling pond by stopping extracting sludge by utilizing the signal of the rate of change in the concn. obtained by differentiating the measured concn. of sludge extracted from the settling pond by a differentiator. CONSTITUTION:The concn. of sludge extracted from a settling pond 1 is given from a densitometer 5 to a differentiator 6, the concn. versus time is differentiated and the signal is inputted to a comparator 7 wherein the signal of the rate of change in the concn. is compared with the desired rate of change for stopping from a setter 8. When the former is lower than the latter, an output is given to a discriminator 9. In the discriminator 9, whether the input from the comparator 7 is lower than the reference value of concn. for stopping extraction or not is discriminated and a command for stopping extraction is given to a sequence controller 11, when the output is emitted from the comparator 7. Whether it is the time to start extraction or the time to stop extraction is discriminated, a command for stopping extraction is given to the sequence controller 11 when it is the time to stop extraction and a command to close is given to an extraction valve 4.
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