Abstract:For the problems of time-consuming,low efficiency,low degree of automation using the traditional PID artificial tuning in the temperature of coal tar in the preparation of activated carbon,designed a PID self-tuning method. Using describing function method based on MATLAB to acquire system amplitude and frequency of self-sustained oscillation,combined with the expanded critical proportion degree method,by regulating hysteresis width and height of nonlinear relay link can make the system rapidly optimal under certain overshoot,programming and realization in PLC. After the test,the anticipated effect has achieved. Through the self-tuning,the adjusting speed of system has been improved,the automation and production efficiency of the preparation process of activated carbon has been improved,and has a certain application value in PID self-tuning in system with time delay of tar temperature in activated carbon.