基于PLC的加热炉温度曲线控制系统设计

Design of the temperature curve control system of the heating furnace based on PLC

摘要:

提出一种加热炉温度控制系统的软、 硬件设计方法。硬件上以PLC为核心,采用V/F转换器和PLC的高速计数功能实现了A/D转换, 并利用PLC的定时器产生脉宽调制(即PWM)波形替代了D/A模块。软件上采用分段拟合的方法修正频率-温度曲线,弥补了常规PID算法的缺陷,实现了温度的闭环控制。降低了系统成本,满足系统控制精度的要求。

Abstract:

The composition structure ,the work principle and the soft design of control system for the heating furnace are introduced briefly. In the system,the frequency signal is gotten from V/F converter used as an A/D (Analog and Digital) converter, and then it is sent to high-speed counter of PLC to measure the temperature of heating furnace. The PWM (Pulse Width Modulation) curve produced by PLC are used to control the temperature of heating furnace as a D/A(Digital and Analog) converter.In the software design, the PID algorithm is applied to form a closed-loop control. Furthermore, the piecewise fitting method is used to make up for the defects of conventional PID algorithm by modifying the curve of frequency and temperature .Experimental results show that these method reduce the cost of control system via replacing expensive analog A/D module and D/A module ,and also obtain better steady-state accuracy and dynamic characteristics．