SCADA(Supervisory Control And Data Acquisition)

INTRODUCTION TO SCADA:

The term SCADA stands for "supervisory control and data acquisition". This system is introduced in the year 1960's. This is an industrial control system where a computer system is monitoring and controlling the process. It gives the graphical representation of the process to a operator. SCADA system is mostly used where the process is spread in wide range of area away from the control room. Modern SCADA systems are designed to access the process data from anywhere in the world using TCP/IP protocols.

COMPONENTS OF SCADA:

1) Supervisory(master) System: This system consists of the servers and softwares responsible for communicating with the field equipments like PLCs, RTUs, Field Instruments and with HMI systems running on the work stations of the control room. The historical data of trends, alarms will be stored in the memory of master system.  In smaller SCADA systems the master system may be composed of a single PC.

2) HMI: An Human Machine Interface is an software used in the SCADA system. The HMI system usually presents the information of the process to the operator graphically in the form of a animated diagrams. This means that the operator can see a schematic representation of the plant or process graphically. Using this, The human operator can control and monitors the process.

figure no.1

The HMI package for the SCADA system is typically includes a drawing program that the operator or maintainance personnel use to change the way these points are represented in the interface. These representation can be as simple as shown in the figure no.1, Which is representing the physical parameters of pressure, temperature, level of tank and the status of motors and valves.

3) RTUs: An Remote Telemetry Units are rugged industrial computers which are connected to the sensors in the process which converts the sensor signals into the digital signal. RTUs provides intelligence in the field and allows the master system to communicate with the field instruments. Its function is to control process equipment at the remote site and acquires the data from the equipments and transfer it back to the master system. RTUs are used where the equipment being controlled is far away from the central unit.

figure no.2

RTUs consists of Telemetry hardware which is capable of sending data to the master system and as well as receiving commands from the master system over large distances. The figure no.2 shows the operation of RTU in various field processes.

4) PLCs: Programmable Logic Controllers are more economical, versatile and flexible than RTUs. It does the job of RTUs and also controls the process when commands were received from the master system. Whereas RTUs are often considered for gathering telemetry data over large areas, Because they use wireless communications. PLC's are not having the Telemetry hardware, So it is not preferred in such applications where the process is in remote area.
The basic operation and role of PLC in the SCADA system is shown below in the diagram.

figure no.3

As we see in the figure no.3, The control action in the field is supervised by the program saved in the memory of PLCs. But using the SCADA system the operator can monitor the process being controlled by PLCs and can change the setpoints, valve control data, pump speed etc in some necessary conditions.

5)COMMUNICATION: The conveying of data from an RTUs to the master station and commands from the master system to RTUs must be done over a communication system. It provides connectivity to the master system to the RTUs/PLCs.

figure no.4

Some of the most widely using communication protocols and cables using in industrial automation applications are,
FOUNDATION FIELDBUS
MODBUS
PROFIBUS
HART
VNET/IP
ETHERNET
TCP/IP
RS232
RS422/485
All these communication protocols and cables are differed with each other according to their communication parameters such as baud rate, trasmission rate, parity bits etc.
Now a days,Modern SCADA systems are using GPRS technology for logging the data from an RTU using Static IP Address.

figure no.5

An static IP address is a unique and fixed IP address assigned to devices so that they can identify and communicate with each other on a network from anywhere.

figure no.5

In the figure(5), We can see the configurations of different communication protocols used in Industrial Automation.

Click here to view and download the Fieldbus Manual

Click here to view and download the Profibus Manual

Click here to view and download the Modbus Manual

APPLICATIONS OF SCADA:

1)Application In Power Plants:
A group of Hydro and Gas generation plants when the load demand exceeds the generating capacity, These plants are considered as peak load plants because these plants can start in no time and deliver power to the grid. These plants are located in the romote locations. These plants are controlled by opening and closing the valves of turbines so that they can deliver the power in peak conditions and can be kept on standby during normal load conditions.

2)Application In Oil & Gas Plants:
Many process control parameters, motors, pumps, valves are spread over the wide area in the field. Control and monitoring applications include turning on and off motors, pumps, valves and gathering information of process parameters(like flow rate, pressure, temperature) continuously and taking certain decisions can be done through SCADA systems.

3)Applications In Pipelines:
Pipelines carrying oil, gas, chemicals and water which are located at varying distances from the plant needs continuous monitoring and control. Control includes opening and closing the valves, starting and stopping the pumps. Monitoring the flowrate and other parameters to avoid leakage in the pipelines by acquiring the data and carrying out suitable controls is done through SCADA systems.

4)Applications In Power Transmission:
Electrical power transmission which is spread over thousands of kilometers can be controlled by opening and closing the circuit breakers and other functions, This is done in master control substation which can control the other substations through SCADA systems.

5)Applications In Irrigation Systems:
Irrigation systems which are spread over wide area can be controlled by closing and opening the valves, gathering the meter values of amount of water supplied and taking the control actions can be done through SCADA systems.


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