Application of relay feedback auto-tuning algorithm in a liquid level PID control system

Liquid level control system which is made up of PLC as controller, frequency transformer as executable device is designed. Its PID control parameters are set on-line using the Relay feedback Auto-tuning algorithm and self-tuning function of Siemens S7-200 PLC. The MCGS monitoring software is used at control system operator station which can achieve the functions such as real-time data acquisition, control parameter input, control mode conversion and so on. In the liquid level control experiment, the setting process of PID control parameters and the control effect of set liquid level are memorized by MCGS monitor software. The PID control parameters which is set by S7-200 PLC realize steady tracking to the set liquid level. The entire system has characteristics of flexible control, high advantages and low failure. It can meet the control requirements of general chemical production process.