| 摘要 |
<p>PROBLEM TO BE SOLVED: To control vacuum pressure in a vacuum vessel exactly over all ranges of a low vacuum range, a medium vacuum range and a high vacuum range by controlling a servo valve for changing air pressure supplied to a pilot valve based on the output of a pressure sensor, in a vacuum pressure controller. SOLUTION: A vacuum pressure control circuit compares a target vacuum pressure value given by an interface circuit with a present vacuum pressure value in a vacuum chamber measured by a pressure sensor, and controls the valve opening of a vacuum proportional opening and closing control valve so that both of them may meet each other. Therefore, the position of the piston is moved vertically to control the stopping position of a poppet valve disc 33. A stainless steel valve disc 34 has a tapered surface 34a, so the cross section of a clearance formed by a valve seat 36 and the tapered surface 34a changes little by little from the stopping position of the poppet valve disc 33. It is thus possible to conduct such control as change the valve opening by a very fine quantity.</p> |
