Millimeter-wave Radiation Meter Constant Temperature Control System Design

Based on the actual demand for a portable radiometer measurement system, a system of constant temperature is researched in this paper, which includes the system simulation, system design and system commissioning work.The constant temperature system will help improve the stability of the radiometer measurement system in the field. The following aspects of work are presented in the paper.In control algorithm of the system, the paper presents principle of traditional PID algorithm and fuzzy control algorithms, and discusses the choice of PID parameters and the foundation of an integrated fuzzy inference system. According to the need for this project, the fuse of fuzzy control and PID control is set forth.In temperature sensing design, the paper selects the German Heraeus company's PT100 platinum resistance, HD421H, as a temperature sensor to design a temperature sensor circuit. Its non-linear error is analyzed in detail and linear approximation is adopted to reduce the non-linear error. Three-point calibration experiment is implemented to confirm the relation of the output voltage of the sensor circuit with a temperature.In control and heating circuit design, AT89C52 is selected for the control system and SG2525 to generate PWM circuit for the heating circuit. The control system samples the output signal of the temperature sensor with A/D converter and implements fuzzy PID control function, with the digital potentiometers ISL90810 to regulate SG2525 PWM duty cycle. The relation of PWM duty cycle with input control parameter is derived in detail, and the control range of the system output is achieved.In simulation, a systematic transfer function is founded by use of Matlab Simlink, and the working performance are simulated of two traditional PID and a fuzzy PID control. According to an actual working environment, a reasonable state of the control table is achieved through the fuzzy PID simulation.In software design, based on simulation results with fuzzy PID algorithm, MCU control software is designed; and in VC++6.0 compiler environment, PC control software is presented which is used with RS232 interface to perform the temperature settings, real-time or intermittent temperature enquiry, sampling moment Settings and other functions.