The schematic of the SCADA system:
Data Acquisition starts from RTUs and PLCs and involves reporting equipment status and reading measurements. This data must then be converted to a format on which the control room operator can make sound monitoring decisions and use the machine-to-human (HMI) interface to set the programmable logic controller to normal.
The SCADA system is usually implemented on Distributed Databases, which contain data elements called tags or points.
A tag or dot is a single output or input value that is monitored and controlled by the system.
These points are either Soft or Hard.
The actual output or input of a system is represented by a hard point, while a soft point is the result of applying different mathematical and logical operators to other points.
These points are usually stored in pairs of values and time labels (Timestamp-Value Pair).
Some of these data sets provide a history of specific points.
It is also common to store additional metadata along with tags.
Additional data can include comments about design time, warning information, and directions to field devices or PLCs.
SCADA system hardware
A SCADA system may have elements of a Distributed Control System. In other words, due to the use of PLCs and RTUs, it is possible to run simple logic processes without the intervention of a master computer. Ladder Logic can be used to program a PLC, which is very simple, unlike Fortran and C languages. An engineer in a SCADA system can design programs and then run them on PLC and RTU.
Compact controllers, such as programmable automation controllers (PACs), combine the capabilities and features of PC-based control systems with one PLC.
RTUs distributed at various substations of the SCADA system use station computers or information processors to communicate with programmable automation controllers, protection relays, and other input / output (I / O) devices.
Scada's philosophy of operation
In some systems, the cost of control system failure is very high or even has very unfortunate consequences.
For this reason, in some SCADA systems, the hardware is resistant to high temperatures, pressures, voltages, and vibrations.
However, in some critical applications, the reliability of the system is enhanced by the use of telecommunication channels and additional hardware.
In these systems, when one part of the system is damaged or malfunctions, it can be quickly detected and then its function is automatically transferred to the backup hardware.
The replacement operation must be performed without disturbing the process control.
SCADA Part 4: SCADA Network Hardware Architecture
SCADA Part 3: SCADA Telecommunications and infrastructure
SCADA Part 2: SCADA system hardware
SCADA Part 1: The concept of the SCADA system
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