Microprocessor control of a small vacuum system

Abstract

A microcomputer has been used to control the pumping sequence of a small vacuum coating plant. The control panel is operated by four push switch controls labelled start, calibrate, closedown and abort. The operator initially prepares the specimen and the coating material inside the vessel then pushes the start switch. The pumping and coating operations are automatically carried out according to a predetermined time sequence. When the coating operation is completed, the vessel is cooled and returned to atmospheric pressure and the operator is summoned to prepare for the next coating operation. At this stage the calibration push switch allows any drift in the electronic monitoring equipment to be corrected. The closedown push switch will systematically shut down the system when all the coating operations have been completed, whilst the abort push switch allow the system to be immediately shut down at any stage in the event of a system failure. The system software and hardware have been described in detail. The software is based upon the Intel 8080 instruction set and is written in a modular format. The software controls the the pumps, valves and pressure gauges so that they operate in the correct sequence for the required time period. All the input/output interface circuits between the microcomputer and the components of the pumping system have been designed using standard TTL circuits. The overall design is extremely flexible and additional monitoring devices and alternative operating schedules may be readily introduced.