What is a SCADA System : Architecture & Its Working

A large number of processes occur in large industrial establishments. Every process, you need to monitor is very complex because each machine gives the different output. The SCADA system used to gather data from sensors and instruments located in remote areas. The computer then processes this data and presents it promptly. The SCADA system gathers the information (like a leak on a pipeline occurred) and transfers the information back to the system while giving the alerts that leakage has occurred and displays the information in a logical and organized fashion. The SCADA system used to run on DOS and UNIX operating systems. This entire process is known as automation. This article discusses an overview of the SCADA system.

What is a SCADA System?

SCADA stands for supervisory control and data acquisition. It is a type of software application program for process control.  SCADA is a central control system that consists of controllers network interfaces, input/output, communication equipment, and software. SCADA systems are used to monitor and control the equipment in the industrial process which includes manufacturing, production, development, and fabrication. The infrastructural processes include gas and oil distribution, electrical power, water distribution.  Public utilities include a bus traffic system, airport.  The SCADA system takes the reading of the meters and checks the status of sensors in regular intervals so that it requires minimal interference of humans.

General SCADA Network
General SCADA Network

History of SCADA

Earlier, the controlling of industrial plants and manufacturing floors can be done manually with the help of analog equipment and push-buttons. As the industry’s size is growing, so they employed timers and relays to provide supervisory control to a fixed level for minimal automation. So, a fully automated with a more efficient system was necessary for all the industries.

We know that, for industrial control purposes, computers were implemented in the year 1950. After that, the concept of telemetry was implemented for data transmission as well as virtual communication. In the year 1970, the SCADA system was developed along with the microprocessors as well as PLC.

So these concepts were fully helped while developing automation that is operated in industries remotely. The distributed SCADA systems were implemented in the year 2000. After that, new SCADA systems were developed to monitor & control real-time data anyplace in the globe.

SCADA System Architecture

Generally, the SCADA system is a centralized system that monitors and controls the entire area. It is a pure software package that is positioned on top of the hardware. A supervisory system gathers data on the process and sends the commands control to the process. The SCADA is a remote terminal unit which is also known as RTU.


Most control actions are automatically performed by RTUs or PLCs. The RTUs consists of the programmable logic converter which can be set to specific requirement. For example, in the thermal power plant, the water flow can be set to a specific value or it can be changed according to the requirement.

 The SCADA system allows operators to change the set point for the flow, and enable alarm conditions in case of loss of flow and high temperature, and the condition is displayed and recorded. The SCADA system monitors the overall performance of the loop. The SCADA system is a centralized system to communicate with both wired and wireless technology to Clint devices. The SCADA system controls can run completely all kinds of the industrial process.

For example,  if too much pressure is building up in a gas pipeline the SCADA system can automatically open a release valve.

Hardware Architecture

 The generally SCADA system can be classified into two parts:

  • Client layer
  • Data server layer

The Clint layer caters to the man-machine interaction.

The data server layer handles most of the process of data activities.

The SCADA station refers to the servers and it is composed of a single PC.  The data servers communicate with devices in the field through process controllers like PLCs or RTUs. The PLCs are connected to the data servers either directly or via networks or buses. The SCADA system utilizes a WAN and LAN networks, the WAN and LAN consist of internet protocols used for communication between the master station and devices.

The physical equipment like sensors connected to the PLCs or RTUs. The RTUs convert the sensor signals to digital data and sends digital data to the master. According to the master feedback received by the RTU, it applies the electrical signal to relays. Most of the monitoring and control operations are performed by RTUs or PLCs as we can see in the figure.

SCADA System Hardware Architecture
SCADA System Hardware Architecture

Software Architecture

Most of the servers are used for multitasking and real-time database. The servers are responsible for data gathering and handling. The SCADA system consists of a software program to provide trending, diagnostic data, and manage information such as scheduled maintenance procedures, logistic information, detailed schematics for a particular sensor or machine, and expert-system troubleshooting guides. This means the operator can see a schematic representation of the plant being controlled.

Software Architecture of SCADA
Software Architecture of SCADA

Examples are alarm checking, calculations, logging, and archiving; polling controllers on a set of parameters, those are typically connected to the server.

SCADA System Working

The SCADA system performs the following functions

  • Data Acquisitions
  • Data Communication
  • Information/Data presentation
  • Monitoring/Control

These functions are performed by sensors, RTUs, controllers, a communication network.  The sensors are used to collect the important information and RTUs are used to send this information to the controller and display the status of the system. According to the status of the system, the user can give the command to other system components. This operation is done by the communication network.

Data Acquisitions

The real-time system consists of thousands of components and sensors. It is very important to know the status of particular components and sensors. For example, some sensors measure the water flow from the reservoir to the water tank and some sensors measure the value pressure as the water is released from the reservoir.

Data Communication

The SCADA system uses a wired network to communicate between users and devices. Real-time applications use a lot of sensors and components which should be controlled remotely. The SCADA system uses internet communications. All information is transmitted through the internet using specific protocols. Sensors and relays are not able to communicate with the network protocols so RTUs used to communicate sensors and network interfaces.

Information/Data Presentation

The normal circuit networks have some indicators which can be visible to control but in the real-time SCADA system, there are thousands of sensors and alarm which are impossible to be handled simultaneously. The SCADA system uses the human-machine interface (HMI) to provide all of the information gathered from the various sensors.


The SCADA system uses different switches to operate each device and displays the status of the control area. Any part of the process can be turned ON/OFF from the control station using these switches. SCADA system is implemented to work automatically without human intervention but in critical situations, it is handled by manpower.

SCADA Components

The SCADA system components include the following.

Supervisory System

The supervisory system works like a communication server among the human-machine interface software within the control room of workstations as well as its apparatus such as RTUs, Sensors, PLCs, etc. Smaller SCADA systems include simply a single personal computer to serve like a master system otherwise supervisory whereas, large SCADA systems include numerous servers, sites for tragedy recovery as well as distributed software applications. The servers are connected like hot-standby formation otherwise dual-redundant to monitor server failure continuously.

RTUs (Remote Terminal Units)

The RTU or remote terminal unit is an electronic device and it is also known as remote telemetry units. This system comprises physical objects that are interfaced through RTUs.

The controlling of these devices can be done through microprocessors. Here, microprocessors are utilized for controlling RTUs which are used to transmit the recorded data toward the supervisory system. The data can be received from the master system for controlling the connected objects.

PLCs (Programmable Logic Controllers)

The term PLC stands for programmable logic controllers which are used in SCADA systems with the help of sensors. These controllers are connected to the sensors for converting the output signal of the sensor into digital data. As compared with RTUs, these are used due to their flexibility, configuration, versatility & affordability.

Communication Infrastructure

In the SCADA system, a mix of radio & the direct-wired connection is used. But, SONET or SDH can also be utilized for superior systems such as power stations & railways. Few standardized 7 recognized protocols are used between the compact SCADA protocols to deliver information simply once the RTUs are polled through the supervisory station.

SCADA Programming

In HMI otherwise master station, SCADA programming is mainly used to make maps, diagrams to provide very important information throughout progression otherwise when event failure occurs. Most of the commercial SCADA systems utilize consistent interfaces in C programming language otherwise derived programming language can also be used.

Human Machine Interface

The SCADA system uses the human-machine interface. The information is displayed and monitored to be processed by a human. HMI provides access to multiple control units which can be PLCs and RTUs. The HMI provides the graphical presentation of the system.

For example, it provides a graphical picture of the pump connected to the tank. The user can see the flow of the water and the pressure of the water. The important part of the HMI is an alarm system that is activated according to the predefined values.

Human Machine Interface
Human Machine Interface

For example, the tank water level alarm is set 60% and 70% values. If the water level reaches above 60% the alarm gives a normal warning and if the water level reaches above 70% the alarm gives a critical warning.

Types of SCADA System

SCADA systems are classified into four types which include the following.

  • Monolithic SCADA Systems
  • Distributed SCADA Systems
  • Networked SCADA Systems
  • IoT SCADA Systems

Monolithic SCADA Systems

Monolithic SCADA systems are called as early or first-generation systems. In these types of systems, minicomputers are used. The development of these systems can be done when common network services are not available. The designing of these systems can be done like independent systems without any relation to other systems.

The data can be gathered from all RTUs using a backup mainframe. The main functions of these first-generation systems are restricted to flagging processes in crisis cases &to monitor the sensors.

Distributed SCADA Systems

Distributed SCADA systems are called second-generation systems. The distribution of the control functions can be done across numerous systems by connecting with a local area network. The control operations can be performed by sharing real-time data & command processing.

In these types of systems, the size and cost of each station are reduced however there were no consistent network protocols. As the protocols were proprietary, fewer people understand the SCADA system security while installation & this factor were ignored largely.

Networked SCADA Systems

The networked SCADA systems are also known as third-generation systems. The networking and communication of present SCADA systems can be done using the WAN system through data lines or phones. The data transmission among two nodes can be done with the help of Ethernet or Fiber-optic connections.

This type of SCADA system uses PLC to adjust and monitor the flagging operations simply once there is a necessity for main choices.

IoT SCADA Systems

IoT SCADA systems are fourth-generation systems. In these systems, the system’s infrastructural cost is reduced by implementing IoT through cloud computing. Maintaining as well as integrating these systems is easy as compared with others.

In real-time, the condition of these systems can be reported through cloud computing. Therefore the implementation of algorithms like intricate control can be done that are frequently used on usual PLCs.

SCADA Security

At present, SCADA networks are used extensively in current industries to check & examine real-time data, industrial processes can be controlled, communicate with devices. So SCADA systems are essential for industrial organizations because these systems include hardware & software. So, SCADA security is also essential in industries.

The term SCADA security is used to protect the SCADA networks which are fabricated with computer hardware. SCADA networks used by some of the systems are electricity, natural gas, etc. The private and government organizations have taken the measures of these networks because of the valuable role to make sure the security of the SCADA systems.

Examples of SCADA Security

The threats that occur in SCADA systems include the following.

  • Hackers
  • Terrorists
  • Malware
  • Error Inside

The weakness of SCADA security mainly occurs because of the following reasons.

  • Poor Training
  • Loopholes Development of App
  • Issues while Monitoring
  • Less Maintenance

The SCADA system can be protected by mapping all present systems, monitoring, and detecting the institute, and create processes for the security of the network.

Difference between PLC and SCADA

The difference between PLC and SCADA include the following.



The term PLC stands for programmable logic controlThe term SCADA stands for Supervisory Control and Data Acquisition
PLC is hardware-basedSCADA is software-based
PLCs are mainly used to control the process of complex industries like motors and running machines.SCADA is used to observe & run the processes of the plant.
The PLC includes Processor, I/O Modules, a Programming Device & Power SupplyThe SCADA system includes three essential components like MTU, RTU, and HMI
There are different types of PLC like fixed or compact & modular.The different types of a SCADA system are monolithic, distributed, networked & IoT
The i/p & o/ps are signified in NO (normal open), NC (normal close) & coil contacts.The input & outputs of SCADA are represented through images.
In PLC, every component can be defined through an address.In SCADA, each component can be defined through the name.

SCDA for Remote Industrial Plant

In large industrial establishments, many processes occur simultaneously and each needs to be monitored, which is a complex task. The SCADA systems are used to monitor and control the equipment in the industrial processes which include water distribution, oil distribution, and power distribution. The main aim of this project is to process the real-time data and control the large scale remote industrial environment. In the real-time scenario, a temperature logging system for a remote plant operation is taken.

Block Diagram of Temperature Control Industrial Plant
Block Diagram of Temperature Control Industrial Plant

The temperature sensors are connected to the microcontroller, which is connected to the PC at the front end, and software is loaded on the computer. The data is collected from the temperature sensors. The temperature sensors continuously send the signal to the microcontroller which accordingly displays these values on its front panel.

One can set the parameters like low limit and high limit on the computer screen. When the temperature of a sensor goes above-set point the microcontroller sends a command to the corresponding relay. The heaters connected through relay contacts are turned OFF and ON.

This is a temperature logging system. Here 8 temperature sensors in multiplexing mode are connected to the microcontroller through ADC 0808. Then the values of all the sensors are sent serially by the microcontroller through Max 32 to the com port of the PC. A Software “DAQ System” loaded on the PC takes these values and show them on its front panel, and also logs them to the database “daq.mdb”.

One can set by the interactive way some parameters like a set point, low limit, and high limit on the computer screen. When the temperature of some sensor increases beyond the setpoint, the microcontroller sends commands to relay driver IC. The heaters connected through relay contacts are (specific for that sensor) turned OFF (or ON in opposite case). High limit and low limits are for alarm. When the temperature goes above the high limit or below the low limit the alarm will be turned on.

SCADA for Remote Industrial Plant
SCADA for Remote Industrial Plant


The advantages of the SCADA system include the following.

  • The quality of service can be improved
  • Reliability can be improved
  • Maintenance cost is less
  • The operation can be reduced
  • Large system parameters can be monitored
  • Manpower can be reduced
  • Repair time can be reduced
  • Fault detection & fault localization
  • It stores a large amount of data
  • As per the user requirement, it displays the data in various formats.
  • Thousands of sensors can be interfaced with SCADA for controlling and monitoring
  • Real data simulations can be obtained by operators
  • Gives fast response
  • It is flexible as well as scalable while adding extra resources.
  • The SCADA system provides onboard mechanical and graphical information
  • The SCADA system is easily expandable. We can add a set of control units and sensors according to the requirement.
  • The SCADA system is able to operate in critical situations.


The disadvantages of the SCADA system include the following.

  • It is complex in terms of dependent modules & hardware units.
  • It needs analysts, programmers & skilled operators to maintain
  • High installation cost
  • Unemployment rates can be increased
  • This system supports hardware devices and restricted software’s


The applications of the SCADA system include the following.

  • Generation and Distribution of Power
  • Public Transport
  • Water and Sewage System
  • Manufacturing
  • Industries & Buildings
  • Communication Networks
  • Oil & Gas Industries
  • Power generation, transmission, and distribution
  • Water distribution and reservoir system
  • Public buildings like electrical heating and cooling system.
  • Generators and turbines
  • Traffic light control system

Thus, this is all about an overview of the SCADA system (Supervisory Control and Data Acquisition). This system is controlled by a computer, used to control as well as monitor different processes in plants. This system uses GUI (graphical user interface), data communications &extended management for monitoring systems. Here is a question for you, what is PLC?

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  1. Supervisory Control and Data Acquisition mechanism plays an important role in determining the processes and control system. It further sends processed information to supervising unit for analytics. Schneider Electric India has helped businesses have a clear vision of machinery operations with SCADA.

    1. Tarun Agarwal says:

      Hi SCADA
      Thank you so much for your response.

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