SCADA systemSCADA (Supervisory Control and Data Acquisition) is a distributed control system at a very large scale. In short SCADA is a central system that controls and monitors a big spread system or process. SCADA systems are used to control and monitor voluminous industrial processes.

SCADA system components

Designing a SCADA system requires an analysis of its three major elements. These include Master Station, Outstations (RTUs), and Communication Infrastructure. In other components a SCADA contains controllers, input / output devices, data acquisition and data storage software, and other network equipment.

Master Station

Master stations are the servers and the workstations running in the control room. Servers contain communication software to communicate with other SCADA equipment including PLCs and RTUs, and also to the workstations. Servers also contain distributed application and disaster recovery software. Workstations run HMI software.

HMI

HMI software can draw the diagram that allows the operator to make any desired change in the interface. This drawing program allows the simple as well as complex representation of the system. The HMI and other SCADA software run on the operating systems supporting servers and workstations.

Outstations

Outstations are usually Remote terminal Units (RTUs) and programmable logic controllers (PLCs). RTUs are attached to the equipment and read the data status and measurements (pressure, current, flow, etc.). RTUs can also send control signals to the attached equipments. These may include speed settings, data storage, turning on/off a switch, setting an Alarm.

SCADA Protocols and Communication Infrastructure

SCADA systems use both wireless and physical media. Ethernet and voice over SONET are the mostly used communication structures. Common protocols for SCADA equipment communication include Conitel, Modbus, RP-570, DNP3, IEC 60870-5-101, and Profibus. Most of these protocols contain support for internet communication.

SCADA system's control sequence

The main control of a SCADA system is in master station. Outstations (RTUs / PLCs) collect information from attached equipment automatically. But servers and workstations containing HMI software in master station can always override outstation control. Master Station maintains a data base of set points. A single input / output value acquired by the master station known as a point. Point can be soft (logical) and hard (physical). Value obtained from physical equipment is hard point whereas value from comparison indicates a soft point in the database. SCADA system equipment is also available from authorized dealers. On the other hand separate devices for also available such as wonderware HMI, Ethernet communication Inc., or Allen-Bradley & GE PLCs.