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What is SCADA? Supervisory Control And Data Acquisition

Supervisory Control And Data Acquisition (SCADA) is a system that uses computers, networks, and specialized hardware to monitor and control the physical equipment of an industrial process.

SCADA System

Table of Contents

It coordinates various pieces of equipment to achieve desired goals, such as improving production or managing resources more efficiently. Then, SCADA uses data from those pieces of equipment to decide how those resources should be managed in real-time.

SCADA systems are often found in power plants, oil refineries, chemical plants, water treatment facilities, and other places with large machinery where control is essential for safety and efficiency.

In the industrial automation pyramid, the SCADA system resides above the plant floor PLCs layer and below the ERP layer:

The utilization of Supervisory Control and Data Acquisition (SCADA) can be traced way back to the 1960s or 1970s. Though the exact date is unknown, it may be thought that SCADA systems were initially used when Programmable Logic Controllers (PLC) were gaining popularity and started to modernize conventional control systems.

But what really is a SCADA system?

Some of the leading SCADA software in the industry

In simple terms, SCADA is application software. This software is installed on a computer called a workstation or node.

The software comprises several components, including a development and runtime environment and an I/O server and license.

These software components are configured to work seamlessly, forming a fully functional SCADA system.

An overview on how a SCADA system work

A SCADA system is custom configured using the development environment. A person with knowledge of the process identifies the monitoring parameters and the control capabilities that need to be reflected in the process mimic design.

This is called the preparation of static graphics and animation. Objects with animation or those that display data and variables are then linked to a Tag.

Cimplicity SCADA
Development environment of Cimplicity SCADA called CIMEdit. It allows designing of custom graphic design and animations

Tags, which are software instrument IDs, are created simultaneously when preparing the graphics and animation. Tags are saved and populated in the tag database.

FactoryTalk View Tags
Tag interface and database of FactoryTalk View SCADA

Typically, the Tag is named similarly to the name of the actual, physical device it represents.

Wonderware InTouch Tags
Tag interface and database of Wonderware InTouch SCADA

The SCADA system communicates with Programmable Logic Controllers (PLC), Remote Terminal Units (RTU), and microprocessor-based electronic devices and instruments.

Communication is initiated by configuring a corresponding Data Server or I/O server. As a general rule, a SCADA system may communicate if both the software and partner device is in agreement with a standard communication protocol.

Wonderware System Management Console
Wonderware’s System Management Console (SMC). It hosts a variety of functions, primarily the configuration of Data Acquisition (DA) or Device Integration products

Once all configurations are completed, the runtime environment is launched. The operator interacts in real-time with the process in this runtime environment.

During the active state of the runtime environment, the I/O server continuously sends and receives data to and from the partner devices. Each available data in the I/O server is passed to the linked Tag, making the data available for display.

All these configurations will be meaningless without a valid license. The License defines the limit of tags that may be declared in the Tag database.

A Tag may represent an actual I/O device. For instance, One (1) controller input and One (1) controller output is equivalent to Two (2) Tags; thus, a controller with 300 I/Os in total will require a minimum of 300 SCADA Tag licenses.

Other licensing procedures include no. of SCADA screens or displays and no. of automation objects.

Functionalities of a SCADA System


Supervise processes that may be composed of single or multiple devices, equipment, machines, and processes. It enables Supervision by providing a process mimic displayed from a central monitoring workstation in a stand-alone, distributed, or networked manner.


It provides supervision, but it also permits the control and operation of different plant elements through the remote workstation.

A Central Control Room using a SCADA system
A Central Control Room using a SCADA system

Data Acquisition

Control system supervision cannot be achieved without Data acquisition. Data from plant elements such as the actual reading of transmitters, the actual position of valves, the operating status of a motor, the current process state, and other parameters must be captured by the SCADA system to provide accurate, real-time information.

These data are acquired by interfacing with PLCs or directly from instruments using a specific protocol supported by the particular device.

Alarm and Events Management

Supervision is not limited to the capability of observing the status of the process elements.

With the use of SCADA, process Alarms and Events may be monitored from the central SCADA workstation.

It gives the plant operator the ability to interact such as acknowledgment and inhibition and, simultaneously, permits the operator to trigger the appropriate action relative to the current alarms and events.

Siemen’s WinCC SCADA Alarm and Events
Siemen’s WinCC SCADA Alarm and Events handling. Notice the capability of this component to quickly depict status and events through color coded animation. Image taken from the Simatic WinCC Process Visualization using Plant Intelligence document.


Trends are used to analyze overall process operation, the performance of a control loop, the sequence of events, and an overview of the reliability and performance of a single instrument.

Trends provide a graphical view of one or more parameters and allow operators to compare, zoom in and out, navigate through time periods, to view specifics of the data with resolutions ranging from milliseconds to a second.

Inductive Automation’s Ignition SCADA Sparkline chart
Inductive Automation’s Ignition SCADA Sparkline chart. Ignition supports other views such as Status chart, Color mapping and standard Trending feature.


SCADA system security varies according to the size of the SCADA system. However, any SCADA utilization is capable of implementing simple security.

Security settings are primarily designed to prevent unwanted access to the SCADA system’s monitoring, control and modification capabilities.

All personnel involved with the operation are given privileges that define the different access levels.

Historian and Reports

Historian allows the acquired data to be saved to a database for later use. In addition, it provides an extended data archive, typically a minimum of One (1) year which may be extended further, depending on the configuration of the SCADA system.

FactoryTalk View Site Edition Historian
FactoryTalk View Site Edition Historian in FactoryTalk VantagePoint Reports. Historian software saves data to a database for an extended period

Web Connectivity

Most networked and modern SCADA supports the design of a web-based dashboard that may be accessed using a standard Web browser.

This dashboard enables remote monitoring and control that is accessible with the use of desktop and laptop computers as well as smartphones and tablets. 

Types of SCADA?

Technology advancements have been introduced, which triggered the existence of different SCADA types. As a result, SCADA systems may be generally classified as Stand-Alone, Distributed, or Networked.

Stand-alone – Stand-alone SCADA operates without interaction with any co-existing SCADA systems.  Though commonly comprised of a single computer, the term stand-alone does not actually refer to the number of workstations used; instead, it depicts that the installed SCADA is not part of a much larger SCADA network. This type of SCADA is still utilized nowadays for simple processes.

Distributed – Distributed SCADA systems utilize the Ethernet network to communicate with other SCADA components, allowing remote access to data, licenses, operational files, and other documents that may be shared in the network.

A Distributed SCADA also allows the same SCADA application to be executed in one or more workstations without conflict, providing flexibility and operational efficiency.

Networked – Networked SCADA systems, similar to Distributed SCADA, utilize the Ethernet network; however, these are the modern versions of SCADA systems wherein a central file repository and database are used to manage the necessary files and data.

System edits can be made once and deployed with a central file repository to which node needs the revision. This is done by assigning each workstation or nodes a specific role in the networked SCADA.

Typical roles of a networked SCADA include an operator workstation, engineering workstation, operator and engineering workstation combination, I/O (Data) server, Historian server, and Historian client.

Components of a SCADA system

Components of a SCADA system vary depending on the type of SCADA deployed; however, some components are typical for each type:

Computers and Servers
Referred to as a workstation or node, a computer, including server-type computers, hosts the components of a SCADA system. Depending on the type of SCADA system used, the number of computers varies.   

Programmable Logic Controllers (PLC)
The majority of SCADA systems communicate with PLCs as the partner device. The SCADA system acquires the data and control points that reside within the PLC memory and display these data in a graphical, easy-to-understand representation.  

Remote Terminal Units (RTU)
Remote Terminal units are intelligent devices that send and receive data to and from instruments and devices and save them to their local memory.

RTUs, in general, do not implement logic, which is its main difference when compared to a PLC. 

Network Elements
Depending on the type of SCADA, network elements may vary. For example, network elements may include network switches, routers, adapters, firewalls, protocol converters, gateways, and other similar devices.


Most SCADA systems are compliant with the OPC (Object Linking and Embedding for Process Control) interoperability.

With this feature built-in, a certain SCADA system is guaranteed to communicate with any controller brand.

This gives any user to capability to select a SCADA that meets their commercial and technical requirement, whether of the same brand or not.

Inductive automation’s built-in OPC
Inductive automation’s built-in OPC. It supports a wide variety of 3rd party products.
Cimplicity’s CimOPCServer Kepware OPC
GE Cimplicity’s CimOPCServer. This is the built-in Kepware OPC software that manages connection and data exchange to different devices

In fact, SCADA applications come with their own OPC or communication management tool.

For Siemens, WinCC has built-in OPC drivers called channel drivers. For FactoryTalk View, RSLinx features an OPC capability, while for Wonderware, OPC drivers were coined as I/O servers, changed to Data Acquisition (DA) servers to OI Objects, collectively known as Device Integration products.

SCADA, Human Machine Interface (HMI) and Distributed Control Systems (DCS)

A SCADA system is situated higher than an HMI and lower than a DCS in terms of application hierarchy and capability.

Sometimes, an HMI is referred to as a SCADA and vice-versa.

Though they have similar primary features to provide real-time monitoring and control, the compact assembly of an HMI is the limit to its performance.

Exceptionally few HMI can perform historization, support web connectivity and handle the connection to multiple controllers simultaneously. Some HMIs may have one but not all of these features.

On the other hand, SCADA utilizes the power of the host computer and operating system, making the operational boundaries much higher than an HMI.

When compared to a DCS, the SCADA is inferior in terms of functionality. As a DCS is a platform, a SCADA is simply software. In fact, to some DCS, SCADA software is only a component.

For instance, Siemens PCS7 uses the Windows Control Center (WinCC), which is also Siemens’ SCADA software. Similarly, Rockwell Automation’s Plant Pax FactoryTalk View (FTView) is their SCADA software as well.

It doesn’t matter whether stand-alone, distributed, or networked SCADA. It remains just a component of their DCS. However, DCS manufacturers, such as Emerson DeltaV and Yokogawa Centum, don’t have a SCADA component that can operate outside the DCS platform.

Other brands, such as Inductive Automation’s Ignition SCADA, are vendor-independent and only manufacture SCADA and connectivity applications.


SCADA is a system that provides real-time monitoring and control. It’s an essential part of engineering projects because it can be used to monitor equipment performance in a process control network.

SCADA systems are complex pieces of software that need to integrate with other hardware components such as RTUs, HMI devices, or DCS platforms for full functionality.

The integration needs to take place through either OPC drivers or proprietary communication management tools from each vendor.

When selecting your next project, make sure you choose SCADA software with all the features you want at a price point that suits your budget!


The difference between HMI and SCADA an HMI is a compact system that manages only data from its controllers and displays it in real-time. At the same time, a SCADA can connect to multiple sites through different protocols and has more powerful features such as historian and web connectivity.

A SCADA system is a software, while a DCS is a platform. Sometimes, a SCADA can be only a software component of the DCS. For instance, Siemens uses its WinCC as their SCADA and DeltaV as their DCS platform.

In process industries, the SCADA system is usually used to control, monitor, or supervise different equipment found on the production floor. These are power plants, refineries, chemical plants, oil and gas production plants, water treatment plants, desalination plants, and many others.

No, not all of them are connected to the internet since they need to be protected first to prevent hackers from accessing critical information.

However, some of these systems have WAN capabilities to establish a connection through VPN or other communication protocols.

In general, these systems are more secure compared with other types of systems out there.

Since these systems provide an operator interface, they will require a lot of resources in terms of memory and processing power. This can cause problems, especially if it is not planned correctly or designed before implementation. Also, like every complex system, it requires maintenance.

The main benefit is that these systems provide an operator interface to process, manage and control equipment from a single location.

This allows companies to monitor their operations from a central location. In addition, it also helps in reducing downtime and loss of equipment or devices since they can be easily monitored from a remote location.

Many companies implement security features to protect their data and information from hackers. However, this cannot entirely prevent hackers from accessing information since they can use alternative channels to get their way into the company’s system.

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Check out our new course:

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