本课题以现有炼镁炉熔炼过程的控制为背景，针对原有的人工控制，系统在长时间工作过程中，人工操作容易出现失误会导致产品工艺的误差，不能够监控系统的运行状态，系统的工艺参数记录困难等问题，按照工艺要求研制一种以PLC和计算机结合的自动控制系统，实现炼镁炉熔炼过程的自动控制，完成了现场的集中管理和分散控制。 介绍了基于计算机—PLC的自动控制系统设计，包括各模拟量的采集，多路电磁阀门的控制，单片机扩展多路串口，系统上下位机的软件设计，通信模块的设计等。 系统以PLC为核心控制器，实时采集炼镁熔炉的温度、压力、各种电量参数等模拟量，但由于这些仪表不是同一家生产，其通信接口不一致。为了现场的布线简单和便于维护，开发了一种单片机扩展多路串口设备，把其他TTL、CAN电平转化为RS485电平，通过RS-485总线传输到PLC中，PLC将数据处理后与预先设定好的控制参数进行比较输出控制12路物料转送阀门，检测与控制加热电极的电压、整流电路冷却系统，加热炉真空度。 探讨了一种基于CAN与232的串行网络系统，连线简单，传输数据快速可靠。研究了如何记录各种工艺参数以及其变化规律，通过数据库绘制工艺过程状态曲线。并且采用什么方法实现自动保存温度、真空度、电压电流等数据，为提高产品质量提供依据。实现如何通过上位机修改PLC的控制参数并且可远程手动控制各阀门的启闭，调节电压升降等。对系统的运行控制方式进行了分析，对由PLC独立进行控制或PLC和上位机同时工作两种控制方式进行了比较。

This thesis takes the present control of the process of the fusion of magnesium-smelting forge as its background, and its main focus is the prior human control, which could easily make mistakes due to long time of operation. As a result of these mistakes, there would be some errors in the technology. Moreover, people may find a lot of difficulties such as monitoring the operation state of the system, and recording the parameter of the technology in human control. According to the requirement of the technology, we have developed an auto controllment system which combines the PLC and the computer. The system is not only able to make self-controllment of the operation process of the magnesium--smelting forge, but also able to do centralized and distributed administration.     This thesis introduces the design of auto- controllment based on the computer and the PLC. It includes a lot of things such as the collection of the analogue quantity, the controllment of the multipath electromagnetic valve, enlargement from the single chip computer to parallel series ,the software design of the Upper and lower computer system, the design of the communication module ,and so on. Take PLC as the central controllment, the system collects the analogue quantity such as the temperature, the pressure, and kinds of Volta parameters of the magnesium-smelting forge in real time .Because these apparatus are produced in different factories, their communication interfaces differ from each other. For easy cabling and convenient maintaining, we have developed a system of enlargement from the single chip computer to parallel series, with which we could convert the level of TTL, CAN to RS485.Through RS485; the level is transformed to the PLC. After data processing, PLC would compare the data with the predetermined controllment parameter and then exports it, and controls the valves of the transportation of the materials in 12 paths .PLC would then measure and control the electric voltage of the heated electrode, the control system of the rectified circuit and the percent of vacuum in the heating forge.      The thesis talks about a serialized net system which can be easily connected and the system can transport data quickly and safely. It discusses a lot of questions such as how to record kinds of technologic parameters and the law in them, how to draw the bifurcation of the operating process according to the databank. Moreover, it studies how to achieve auto -preservation of dates such as temperature, percent of vacuum, electric pressure and current to make a foundation for the improvement of the quality of the production. The question how to use the computer to modify the control parameter of the PLC and how to achieve the controllment of the opening and closeness of the valve and the accommodation of ups and downs of the electric pressure by distensile hand operation. It analyses the way of controllment of the operation of the system. And it makes a comparison between the controlling ways, one of which is independently controlled by PLC, and the other is controlled by the cooperation of PLC and the computer.