SCADA Systems

The acronym SCADA stands for Supervisory Control and Data Acquisition. This term refers to a control system; a computer system monitoring and controlling different processes. Generally this process can be industrial, infrastructure or facility.

Industrial processes involve manufacturing, production, power generation and fabrication.

Infra structure processes can involve water treatment, oil and gas pipelines, electrical power distribution and communication systems.

Facility processes include monitoring and controlling HVAC, access, and energy consumption.

The SCADA systems control and monitor not only processes but also areas and complexes. A variety of sensors help the system to monitor every part of the process while the control action is executed by Programmable Logic Controllers (PLC). For example, a SCADA system monitoring and controlling a water pump system has pressure sensors to monitor the water pressure inside the pipes and a PLC to run or stop the pump according to the user set points. The SCADA system also has an HMI (human machine interface) that bring to the user simple feedback information. What’s more, the HMI allows the user to change and place the set points of the process.

The process of data acquisition begins at the sensor and involves sensor readings and equipment status reports that are communicated to SCADA. After this the information is processed and formatted in a way that the operator can make decision to adjust or change the set points of the systems. This information is presented to the operator through the HMI screen. Data may also be stored and used to create databases.

In the example from above, level sensors read the water tank's level. When the level is low, the controller activates the water pump and turn off the heater. When the water level reaches the high sensor, the water pump turns off and the heater starts working again. While this process is running, the SCADA software installed on the computer creates a database of every event of the process, when the sensors switch, when the motor runs or stop, when the heater is on or off, etc.

These databases contain data elements called tags or points, thus these databases are commonly named tag database. Every tag or point represents a single input y output value controlled by the system. Points are normally store as value-Time pairs, this means a value and a time stamp when it was recorded or calculated. It is also common to add comments and alarm information to the stored tags.

SCADA Architectures

Through time SCADA systems have evolved as follows:

• First Generation: “Monolithic”

In this generation, computing was done by mainframe systems. At that time networks didn’t exists, thus SCADA systems were completely independent with no connectivity to other systems. This generation of SCADA System is considered redundant since a back-up mainframe system was connected at the bus level and was used in the event of failure of the main mainframe system.

• Second Generation: “Distributed”

In this generation, multiple stations were connected and the processing task was distributed between them. All these stations were connected through LAN and they shared the information. Each station had a particular task to develop, making size and cost less than the cost of the mainframe used in the first generation.

• Third Generation: “Networked”

These are the current generation of SCADA systems. In this generation de SCADA system uses open standard and protocols to connect the different components. What’s more, it is easier to connect third party peripheral devices like printers, disk drives and many more. WAN protocols are used for communication between the master station and communication equipment. An example of this protocol can be the Internet Protocol (IP), due to this protocol SCADA system can be remotely accessed and controlled.