图1.1 加热炉温度控制系统基本组成
加热炉温度控制实现过程是:首先温度传感器将加热炉的温度转化为电压信号,PLC主控系统内部的A/D将送进来的电压信号转化为西门子S7-300PLC可识别的数字量,然后 PLC将系统给定的温度值与反馈回来的温度值进行比较并经过PID运算处理后,给固态继电器输入端一个控制信号控制固态继电器的输出端导通与否从而使加热炉开始加热或停止加热。既加热炉温度控制得到实现。其中PLC主控系统为加热炉温度控制系统的核心部分起着重要作用。
系统设计目标及技术要求
本系统应能够控制在设定值的±5℃的误差范围内并且具有温度上下限报警功能和故障报警功能。
The application of Siemens S7-300 in temperature control
Abstract
Temperature control system has been widely used in the industry controlled field,as the temperature control system of boilers and welding machines in steel works、chemical plant、heat-engine plant etc. Heating-stove temperature control has also been applied widely in all kinds of fields .The application of this aspect is based on SCM which is making the PID control, yet the hardware and software design of DDC system controlled by SCM is somewhat complicated , it’s not an advantage especially related to logic control, however it is accepted as the best choice when mentioned to PLC.
The furnace temperature of heating-stove is a large inertia system,so generally using PID adjusting to control. With the expanding of PLC function, the control function in many PLC controllers has been expanded. Therefore it is more reasonable to apply PLC controlling in the applicable fields where logical control and PID control blend together. The design has utilized the control system with which Siemens S7-300 PLC control the temperature heating-stove. In the first place this paper presents the working principles of the temperature control system and the elements of this system. Then it introduces Siemens S7-300 PLC and the specific design procedures of the hardware and the software.
Key words:Siemens S7-300 PLC,PID,temperature pickup, solid state relay