Graphite furnace power supply fuzzy - PID control system

The graphite furnace power supply automatic control system is built around an 8031 single-chip microcontroller, with additional peripheral interface and drive circuits to support its operation. The control system consists of a circuit box that includes various functional modules such as the serial communication circuit, output circuit, analog input circuit, keyboard display unit, switch input/output circuit, and more. These components work together to monitor and regulate the temperature and performance of the graphite furnace. The system receives control commands from a host computer via a serial communication interface. The keyboard and display unit allows operators to input control instructions, view the current temperature, and monitor the operational status of the furnace. The switch input/output circuit collects real-time data about the furnace's operating conditions, communicates with external devices like the autosampler or atomic absorption spectrometer, and sends control signals to the furnace and other connected equipment. The analog input circuit measures the temperature signal and processes it using a control algorithm to generate the appropriate control output. In terms of software design, the system employs a fuzzy logic-based composite control strategy to achieve precise temperature regulation. This approach combines the advantages of fixed-value control for fast response during large deviations and fuzzy control for improved stability and reduced overshoot when the system approaches the target. The fuzzy controller operates within a limited domain, where linguistic variables are used to represent error values, increasing the system’s sensitivity and accuracy. When the deviation enters a steady-state region, the system transitions to a proportional-integral (PI) control mode to eliminate any residual error. The parameter self-tuning fuzzy controller features a two-level structure: the lower level handles the fuzzy control logic, while the upper level adjusts the controller parameters based on predefined rules. These rules are expressed in linguistic terms and are implemented through a lookup table generated by offline computation. During real-time operation, the system quantifies the error and uses the lookup table to determine the appropriate control action and parameter settings, enabling efficient and accurate control of the industrial process. The controller itself is a PID-type regulator, widely used in industrial applications. In a digital control system, the controller operates using difference equations, with outputs calculated based on the current and previous error values. To optimize performance, the system applies a parameter tuning algorithm that adjusts the controller gains based on the system’s response characteristics. Experimental results demonstrate the effectiveness of the system in online analysis and testing. The power supply can handle multiple heating steps, with each step customizable in terms of temperature and control mode. It offers a wide temperature range (from room temperature to 3000°C), high heating rates, and excellent temperature control accuracy. The system also compensates for voltage fluctuations and resistance changes in the graphite tube, ensuring stable atomization and accurate measurements. By integrating infrared temperature sensing and advanced fuzzy control techniques, the system achieves superior performance, making it a reliable solution for analytical instruments. The technology has been successfully applied in commercial systems, improving the efficiency and accuracy of light-controlled graphite furnace operations. References: Li Hua. *Practical Interface Technology of 0351 Series Single-Chip Microcontrollers*. Beijing: Beijing Aerospace University Press, 1993. Zhu Liangzhu. *Analytical Instrument Manual*. Beijing: Chemical Industry Press, 1997.

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