An automatic pressure controller for vacuum systems

Abstract

This paper describes the development of a closed loop servo-system designed to control gas throughput so as to maintain a constant pressure in a dynamic vacuum system. It is designed to work with pressure gauges having an electrical output signal and gas inlet needle valves adaptable for drive by a small servo motor. Traditional principles of operation are adopted, the gauge output signal after amplification being compared with a reference voltage. The difference between the two, controls the drive to the motor. The motor drive is in such a direction as to tend to maintain the pressure gauge output voltage equal to the reference. It is important that the system provides a rapid and stable closed loop response for widely varying types of operation with gauges having a fast response (e.g. ionization types) or slow response (e.g. Pirani type) and also with both long and short vacuum time constants.