| Currently, the main method of gas mixing ratio control in industrial production is to control the flow of two different kinds of gas. The traditional gas mixing ratio control measures to produce industrial standard gas were the method of needle-control and potentiometer-control etc which were very complex and difficult to control the accuracy. In order to satisfy the need of automatic gas mixing ratio control, we designed a kind of instrument to fulfill the automatic gas mixing ratio control which has a high accuracy.Based on the research of detection technique, mass flow gas mixing ratio control fundamentals and gas mixing ratio control algorithms, this paper mainly introduced an automatic mass flow gas mixing ratio controller which used micro controller. The instrument used these below to assure the instrument's high accuracy:1. High-accuracy A/D and D/A chips in its high speed hardware design to make sure the controller's accuracy.2. Using mass flow compensating algorithm, self setting Fuzzy PID control algorithm in its software design which can reduce the effect of nonlinear to the gas mixing ratio control.3. Using self setting Fuzzy PID control algorithm which is good to reduce the steady-state error of the system and good for its dynamic response character.Due to its complex process, mass flow compensating algorithm and self setting Fuzzy PID control algorithm were used to modify and control the PID parameter which can improve the noise rejection ability and the robustness of the system.The design completed the hardware and software of intelligent gas mixing ratio controller circuit which based on mass flow theory. It fulfilled the function of automatic gas mixing ratio control and the testing result achieved the performance index which was expected. It shows in its error analysis and testing results that this instrument can control the concentration of the mixture at any level. The repeatable accuracy of 0.2% can be reached.
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