Three-layer PLC/SCADA system Architecture in process automation and data monitoring

This paper presents the State-of-the-Art and recent trends of SCADA system Architecture, which is usually three-layer SCADA system architecture depending on open system technology rather than a vendor controlled, proprietary technology. A Real-time Industrial process is simulated (boiling system), and a complete three-layer model SCADA system is developed for this process, supervision control layer, Process control layer, and field instrument layer. National Instruments, Labview with the associated data logging and supervisory control toolset (DSC) is used to develop the SCADA/HMI in supervision layer. Industrial programmable logic controllers (PLCs) from SIEMENS (S7-CPU222 and EM231) and related software package are used to build up process control layer. Finally simulation unit is designed and developed to be used as field instrument layer. OPC service protocol (open standards protocol) is used to solve compatibility problem raised from different vendors' tools.