Research And Realization Of Wide-range Composite Vacuum Gauge Based On Digital Closed-loop Control

Composite vacuum gauge is one of the tools used to measure the degree of vacuum, whose performance will directly affect the quality of the completion of scientific research production tasks. With the development of science and technology, it has a certain practical significance to further improve the measuring indexs and degree of digitization of the gauge.The study and design of a wide range vacuum gauge combining ionization gauge with resistance gauge is presented in this thesis.Research is mainly done on the emission current stability control and the ion current detection circuit, which have an direct effect on the measurements of high vacuum measurement in the thesis.Firstly,the requirement of emission current stability is clearly defined and common control algorithms are analyzed in feasibilility application in emission current stability. Combined with the controlled object characteristics,decide on using Fuzzy-PID algorithm and accomplish its functional simulation,and the digital closed-loop stability control of emission current is realised on the MCU.Secondly,after the analysis of the generation principle and detection influencing factors of ion flow signal,the improved ?-? conversion method based on T-type resistor network is selected as an ion current signal detection scheme and switch of circuit transimpedance gain and multi-stage filter to suppress noise are designed,making the circuit measurement range from picoamp to microamp.The composite vacuum gauge overall test consists of test of ion current signal detection module circuit,stable emission current functional module circuit and the whole systems.Some conclusions can be drawn from the test results-the measurement range of ion current signal is 1pA to 6uA and its measurement resolution is 0.2pA and that its noise is less than 1.5mV.For ion gauge,the displaying values of emission current and the potential of accelerating electrode and the cathode to ground have an error less than±0.8% and so is with time stability.For resistance gauge,in the main measuring range from 1Pa to 103Pa, the displaying values have an error less than±10%.For ion gauge,in the measuring range from 10-8Pa to 10-1Pa, the displaying values have an error less than ±1%.The test results satisfy the national standards and meet the general requirements of vacuum measurement in industrial production and scientific research.