Automatic control of gas pressure in a vacuum system

This paper describes the development of a microprocessor based system to be used for the automatic setting of the gas pressure within a vacuum chamber.The requirements of the system have been presented by five modes of operation which are easily set up by thumb wheel and on/off switches on a panel. The microprocessor system automatically balances the rates of the pumping system and gas inlet to set and maintain the requested gas pressure. The gas inlet needle valve is controlled by either an ac or de motor. The use of computer software allows the system to be readily adapted for use with the commonly used needle valves, pressure gauges and pumping systems. It allows for non linear transducers and mechanical wear and additional modes of operation may be easily added when required. The system is intended for use as a subsystem of a microprocessor controlled vacuum system for laboratory or industrial use.The technique has been illustrated by controlling the pressure over the range 1–20 torr in a conventionally pumped vacuum system.