Nowadays, various control systems of DCS come into being in view of various conditions and various network forms through Bus Technology to achieve automation of production and management in factory. Existing DCS based on original control system in which PLC is widely used mode of SCADA, that is to say this kind of mode is composed of configuration software and PPLC. The SCADA mode is composed of host computer and PLC. Host computer contains master station and slave station. PLC as a lower computer to control real device, such as batching system of raw materials, kiln of coal mill, ball milling, shaft kiln, etc. due to openness and performance price ratio, this kind of DCS is widely applied in middle and small process control system, subsystem of large process control system in cement factory.
In the early 1980s our country began to import complete sets of production equipment for steel in which PLC is used for control system. At that time, there is tens of kind of brands of PLCs containing up to two hundreds of PLCs on a set of equipment. Nowadays, in view of advantage of combination with real machine PLC as lower computer has been used widely in production line for steel. PLC has played an important role in every procedure and machine, such as controlling temperature and pressure in boilers, lifting electrodes, feeding oxygen lance for steel, controlling cooling bed and etc.