Perhaps the most common architecture for SCADA (Supervisory, Control and Data Acquisition) system is a hierarchically organized structure. Typically we find a central control unit that contains the high level operation functionality as well as the control center with the interfaces for the process operators. At the heart of this part of the SCADA system we find the database with the reflection of the process status. Connected to this database various kind functionality is connected from simpler sequential steering algorithms and alarm monitoring to distribution. In addition, there are information and functionality for performing data engineering tasks.
Technically, this software is divided on a number of hardware units. How many is depending on the size and complexity of the process that is being controlled. The central unit is collecting all its information from varying numbers of local field site or sub stations. These distributed nodes are communicated to with some sort of wide area network solution.
Each field site can then be more or less complicated and containing a whole local area network solution with a large amount of intelligent electronic devices as in power substations or just single and more simple remote terminal units. The common denominator for the field sites is that they are managing the fast and time-critical aspects of the process. Field devices control local operations such as opening and closing valve and breaker, collecting data from sensor systems, and monitoring the local environment for alarm conditions.
As mentioned, the SCADA systems are not operating stand alone. Today are almost all SCADA systems interconnected with corporate office networks or possibly directly to the internet. Several control centers are also typically connected to each other.