A process control or automation system is used to automatically control a process such as chemical, oil refinerys, paper and pulp factories. The PAS often uses a network to interconnect sensors, controllers, operator terminals and actuators. A PAS is often based on open standards in contrast to a DCS (Distributed Control System), which is traditionally proprietary. However in recent times the PAS is considered to be more associated with SCADA systems. PAS is the lowest level of automation, while MES (Manufacturing Execution System) is considered to be directly positioned above a PAS.
