Graphite furnace power supply fuzzy - PID control system

The graphite furnace power supply automatic control system is built around an 8031 microcontroller, with extended peripheral interface and drive circuits. The control system’s circuit layout is illustrated in Figure 1. The system receives control commands and processes input signals from various sources, including temperature sensors, switches, and communication interfaces. It also provides output signals to manage the furnace's operation, ensuring precise temperature regulation. The control unit includes a single-chip microcontroller with program memory and data storage. A keyboard and display interface allows users to input commands, monitor temperature, and view operational status. The switch input/output circuit collects status information from the furnace power supply and connects it with external devices such as autosamplers or atomic absorption spectrometers. The analog input circuit samples temperature signals and processes them through control algorithms to generate appropriate control outputs. Serial communication is used for interaction between the furnace and a general-purpose computer, enabling direct control via the microcomputer. In terms of software design, fuzzy logic combined with PID control is implemented to achieve both fast response and high accuracy. When the deviation is large, fixed-value control is applied to speed up the response. As the deviation decreases, the system transitions to fuzzy control, enhancing stability and reducing overshoot. The fuzzy control domain is narrowed down by increasing the number of linguistic values, improving sensitivity and precision. Once the system reaches steady state, the controller switches to a proportional-integral mode, which helps eliminate steady-state error. The parameter self-tuning fuzzy controller uses a two-level structure: the lower level performs fuzzy control, while the upper level adjusts parameters based on linguistic rules. Parameter tuning follows specific rules that are derived from linguistic descriptions. These rules guide the adjustment of proportional, integral, and derivative gains. The control algorithm uses approximate reasoning synthesis to compute control actions and parameter settings offline, storing results in a lookup table for real-time application. This approach ensures efficient and accurate control in industrial settings. Experimental results show that the system achieves excellent temperature control, with a range from room temperature to 3000°C and a control accuracy of less than 1°C. The system is capable of setting multiple heating steps, each with customizable temperature and control modes. The use of infrared temperature sensing and fuzzy logic has significantly improved the furnace's performance, making it immune to grid voltage fluctuations and graphite tube resistance changes. This advanced control system has been successfully applied in online analysis and testing by companies such as Nishimzu. It offers reliable and consistent temperature control, enhancing the accuracy of atomic absorption measurements. The system is now available in the market, offering a powerful solution for analytical instrumentation. References: Li Hua, "Practical Interface Technology of 0351 Series Microcontrollers", Beijing: Beijing Aerospace University Press, 1993. Zhu Liangzhu, "Analytical Instrument Manual", Beijing: Chemical Industry Press, 1997.

Stainless Steel Pan

Jiangmen Vanky Stainless Steel Products Co., Ltd. , https://www.vankystar.com