The Design And Application Of PLC Based Air Conditioning Control System In Semiconductor Cleanroom

Semiconductor clean room takes the role of clean class, temperature and humidity control to provide excellent IC production environment. Since qualified clean room parameters rely on Air Conditioning System, designing high reliability and performance Air Conditioning Control System will be the focus during clean room construction phase.The paper is based on a 300mm Wafer Fab FMCS (Facilities Management Control System) project and presents the practical application of distributed PLC control system in semiconductor clean room. It provides temperature, humidity and positive differential pressure real-time control and monitoring, reduces those parameters fluctuation impact to production, realizes energy conservation, and obtains better economic benefits.Regarding to control philosophy, Dew point is defined as critical parameter to decouple temperature and humidity via psychrometric chart. Dehumidification mode is designed to optimize air handling process to avoid humidification and dehumidification mode switch over frequently during season alternant period. PID cascade control methodology is applied for Dew point and positive differential pressure control. Base on actual Air conditioning pipes layout, MAH (Make-up Air Units) group control strategy is proposed to ensure stable fresh air supply.PLC control system adopts ControlLogix framework from Rockwell. It’s designed as CPU rack and network dual redundancy to achieve bumpless switchover once hardware fault generated. Structured and Standardized programming are applied for it as well. SCADA system adopts GE Cimplicity Server/Client architecture via OPC communication technology, which could supports multi-tasks handling and multi-users access. Alarm paging system can send real-time alarm message to operation team, when control system hardware fault and field equipment failure and clean room’s parameters out of spec alarms are generated.The whole system keeps excellent running since it has been put into operation, the quality and performance fully meets design requirement to ensure clean room parameters fluctuation within specification.