| 摘要 |
PURPOSE:To prevent the excessive flow quantity at the time of activating and to improve the life of respective pieces of equipment in a system by selecting a flow quantity control means, executing the flow quantity control at the time of activating a vacuum pump and when a system inner pressure arrives near the set value, selecting a pressure control means and changing over it to a pressure control. CONSTITUTION:When a vacuum pump 7 is activated, an activating signal (d) is inputted to a vacuum control device 12 and an internal signal selecting circuit 17 changes over a changing-over circuit 16 to a flow quantity control system. Then, a flow quantity signal (c) is inputted from a flow quantity signal converter 13 to a flow quantity control circuit 15, the deviation with a rating flow quantity is control-operated and by the output, the opening of a control valve 10 is adjusted. As the result, a flow quantity to flow at a system 1 in accordance with a pipe 6 is controlled to a constant rating flow quantity. When the pressure in the system 1 is descended near a target vacuum degree, the signal selecting circuit 17 changes over the changing-over circuit 16 to a pressure control system. Thus, at this time, a pressure signal (a) is inputted from a pressure signal converter 11 to a pressure control circuit 14, the deviation with the target vacuum degree is control-operated, the opening of the control valve 10 is adjusted by the output and the excessive flow quantity is eliminated.
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