| 摘要 |
PURPOSE:To make cooling water flow controllable irrespective of a variation in suction pressure as well as to improve a water-saving effect ever so better, by letting the setting temperature go up to an allowable maximum extent at a time when control shifts to a nonstable region due to the suction pressure variation in a compressor. CONSTITUTION:In time of normal operation of a compressor 20, the setting temperature given by an SV setter is set down as an SV value whereby a PID calculator 12 is set in motion, thus a cooling water flow rate is PID-controlled. When the cooling water flow enters a nonstable region as suction pressure in the compressor 20 is varied, a regular deviation is produced between a PV value and the SV value. Thereupon, a fact that this deviation becomes more than the specified value is detected by a comparator 8, and when a timer 9 is turned to ON continuously for the specified time T1 long with the deviation, a switch 4 is selected from the terminal A side to the B side. On the other hand, when the deviation becomes less than the specified value, a switch 6 is likewise selected to the B side with each action of a comparator 8 and a timer 10. With this constitution, a specified value epsilon1 is added to the SV value or a specified value epsilon2 is subtracted from the SV value and made so as to be compensated.
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