DDC, developed from PLC, is dedicated to industrial automation. In China, almost all industrial production line control systems, thermal power plant control systems and steel plant control systems have applied PLC systems, and at present, a considerable number of building control systems have also applied PLC systems. Building automation DDC is developed from PLC by manufacturers according to the characteristics of building automation. The difference with PLC is that it only solidifies some internal programs, but it also lacks the flexibility and ability of PLC to deal with complex electromagnetic interference environment.