PLC Programming

SCADA System (Supervisory Control and Data Acquisition): What is SCADA?

SCADA stands for “Supervisory Control and Data Acquisition”.

Engineers usually shorten that long name to “SCADA System”, or simply “SCADA”.

The basics of SCADA include its systems and architecture, applications and programming. These are the topics covered here.

I’ll explain how SCADA systems work and what they do for both the technical and business sides of a company.

Companies often overlook the business side and miss opportunities to make or save money as a result.

Start with what a SCADA system does.

Content:

What is a SCADA System?

A SCADA system monitors and controls equipment and collects data. Its name, Supervisory Control and Data Acquisition, describes these functions. Factories widely use SCADA to monitor and control machines and production lines. To understand where it fits and how it is used, it helps to place it within the automation pyramid.

In the automation pyramid, SCADA occupies the monitoring and supervising level. This concept, published in ISA-95 and IEC 62264-3, describes how different systems work together. Information systems for business, planning and logistics sit at the top, with operational systems at the bottom. SCADA is in the middle, where IT (information technology) meets OT (operational technology). That middle position explains why SCADA connects operational equipment with the information used to run the business.

SCADA System in the Automation Pyramid from ISA-95 (IEC 62264-3)

Operational technology, including PLCs and sensors, sits below SCADA. The SCADA system monitors and controls that equipment while exchanging information with the MES or ERP system above it. That information supports business and planning, such as an order sent to production.

How does a SCADA System work?

SCADA connects information with operations. Its basic functions are exchanging information, monitoring and control. Monitoring and control are the uses you will see most often.

An operator usually sees SCADA as a screen, often several screens. These let the operator monitor and control the relevant components of a unit, machine or entire plant. One way to display them is a P&ID (piping and instrumentation diagram). The operator must be able to understand each part of the display and what it monitors or controls.

SCADA system with PI&D for controlling and monitoring

These screens are HMIs, or human-machine interfaces, connecting the operator with the machine. Older HMIs consisted of push buttons and control lamps. A touchscreen at the machine or in a control room is now common.

If the screens are HMIs, what makes the system SCADA?

SCADA Architecture

An HMI is part of SCADA. The HMI is the screen or interface, while SCADA is the application or system behind it. Several HMIs can belong to a single SCADA system, each monitoring and controlling a different part of the plant.

SCADA’s architecture includes an infrastructure of communicating devices. The application typically runs on a server, with clients such as desktop computers and screens connected as HMIs. PLCs and RTUs also connect to that server. Through these connections, the SCADA clients let you monitor and control operations. The screens are therefore the part the operator uses, while the server and connected devices provide the system behind them.

A remote terminal unit, or RTU, resembles a PLC. It accepts signals from connected sensors and converts them into digital data for the SCADA system to access.

The development of SCADA explains how its early systems grew into the architectures used today.

1st Generation: Monolithic
2nd Generation: Distributed
3rd Generation: Networked
4th Generation: Internet of things

SCADA’s history shows its development from simple monolithic systems to cloud-based infrastructure. Although fourth-generation systems have arrived, many installations still use third- or even second-generation designs. Anyone working with SCADA therefore needs familiarity with the older systems as well. Understanding the changes between generations helps you recognize the architecture of an installation you are working with.

Monolithic Architecture

The first SCADA systems had only one supervisory station. It was back then when PC’s and networks didn’t exist. Instead of PC’s mainframe stations were used. The function of these early systems were limited to monitoring sensors. You will only find these systems in museums now a days.

First generation SCADA architecture with an IBM mainframe computer

Distributed Architecture

Local Area Networks (LAN) made distributed SCADA possible. Instead of a single control and supervisory station, a system could have several. The network linked these supervisory stations so they could communicate with each other. Those connections made communication between stations part of the SCADA system instead of keeping supervision at one station.

Second-generation SCADA systems are rare, but remain in use today.

Networked Architecture

As network technology and protocols developed, Wide Area Networks (WAN) expanded the ways SCADA systems could communicate. A system could cover several plants in distant locations as well as a single plant. With networked architecture, operators can access data and supervision from anywhere, including a location away from those plants. The control and data are no longer limited to access from a single plant.

Networked Architecture of a SCADA system, where control of multiple plants is centralized

Most SCADA installations still use networked architecture. The move toward IoT is growing, but much of that transition remains ahead.

Internet of Things (IoT)

The 4th generation is the SCADA architecture being built now, as part of the Industry 4.0 revolution. It uses Internet of Things (IoT) and decentralized data communication. These technologies allow more freedom and flexibility in how the architecture is arranged.

Industry 4.0 where all components are interconnected and can communicate with the SCADA system at all times.

Traditional SCADA architecture centralizes control and monitoring (data acquisition) in one system or application. IoT moves that design toward decentralization, with every component able to communicate with every other component.

Although this architecture is the future of automation, it still has many security issues. SCADA data often has high business value and is sensitive. Moving it to the cloud requires strong security.

SCADA Software

Real SCADA applications show the range of work these systems can handle. A few large providers lead the market, and many have scalable solutions for different requirements. Some applications suit large sites with multiple servers and clients, while others work best on smaller sites or applications. The scale of your site affects which application makes sense, even when the provider can supply solutions at several levels.

Choosing SCADA software involves technical requirements and business needs. Begin with the following question: It helps frame both sides of the decision around what the system must actually do.

Which variables do we need to monitor and control to support the process and the business? Write that specification before considering which SCADA software to use.

Lifespan of the SCADA software

The software’s lifespan is another consideration people often miss. A SCADA system can require a large investment, with an expected working life of between 5 and 15 years. That expected lifespan affects the choice of software as well as the cost of the initial system.

As we all know technology is developing faster than any other industry. In fact technology doesn’t only evolve fast, it evolves exponentially faster. Just take Moore’s Law as an example. The processor of computers double the amount of transistors each year making them exponentially faster.

Rapid changes in technology can make older methods outdated. Equipment that was advanced five years ago might already seem slow or out of date.

Request for Information (RFI)

RFI or Request for Information is a business term for describing what vendors and suppliers can provide. When choosing SCADA software, you can use it to compare the capabilities of the vendors you are considering.

For example, if your SCADA system is expected to last 10 years, check that the vendor can provide support and updates throughout that period. You also need the ability to expand it during that time. Those capabilities need to remain available for the system’s expected life, rather than only when you first install it.

Historian Software

In SCADA software, a Historian or Historian Software logs data collected through the field data interfaces. You will encounter these terms often when working with SCADA solutions. The historian is the part that keeps the collected data as a record.

A historian saves timestamped data, often in a database. Those timestamps let you use the recorded data for trends, analytics and logging.

Many SCADA applications and industries depend on historian software for data logging. Industries such as food and pharma also have legal logging requirements (FDA 21 CFR Part 11). The standard for batch control ISA-88 shows an example of implementing that logging.

Companies can analyze the historian’s logged data to improve maintenance plans and optimize production. That makes the collected data worth a lot to the business. The record gives you something to examine after collection, rather than only viewing the current data on the screen.

If maintenance work or supplier payments become disputed, preserve the relevant operating logs alongside invoices and bank statements. Your technical team can explain the machine records, while your legal team uses forensic bank statement analysis to trace the associated payments. Keeping both sets of evidence helps separate what happened on site from what was paid.

SCADA Technology

SCADA combines technologies for logging and storing data with communication protocols and standards for accessing it.

Whether you program SCADA or choose a system, you need to understand these technologies. In this setting, a newer technology does not always make a better choice.

Updated technology is almost always an advantage when buying a computer. SCADA has different demands: its many components must work together across an extensive system, and that system must remain secure. A change in one part of that system therefore has to fit the components it works alongside.

Compatibility and security can make stable, secure technology a better choice than the latest option. Lower-level components, especially PLCs and RTUs, may not support the newest communication technologies.

Database

A database usually stores the data SCADA collects. You can retrieve it later for reports and analysis. SQL is the main database technology SCADA systems use, so you may already be familiar with an SQL database. The same stored information can then be used when you prepare a report or examine how the process has behaved.

SQL, short for Structured Query Language, is a programming language for managing database data. It lets you insert, remove and edit data, as well as import or export it. SCADA uses SQL commands to perform those database operations.

Although other query languages exist, SQL is by far the most widely used today for SCADA and database management generally. You can host an SQL database on your own servers or in the cloud.

OPC and OPC UA

SCADA needs to access data from the PLCs and RTUs in the field, so compatibility with those platforms matters. OPC is one of the main technologies used to provide that access. The field devices need a way to supply their data that the SCADA software can use.

OPC, or OLE for process control, is a standard for accessing data in field devices such as PLCs and RTUs. A SCADA system usually communicates with the PLC through OPC server and client technology, specifically OPC DA (data access).

The PLC is set up to be an OPC server which will then translate the data to fit the OPC protocol. In your SCADA system on the other hand you will have an OPC client that can access those data via the OPC protocol.

Most modern PLCs support OPC, which lets you choose a SCADA system from a different vendor than the one that supplied your PLCs.

Alarm Management

Alarm management covers the handling of alarms, which almost all SCADA systems include. It includes setting and resetting them and assigning their priorities.

System-defined alarms concern the hardware’s status or the system itself. User-defined alarms are those the user defines and programs.

Discrete and analog alarms are user-defined alarms. A discrete alarm is triggered by a bit’s digital status, while an analog alarm responds to a value exceeding a defined limit.

Many SCADA systems restrict who can reset an alarm. An alarm often indicates a fault that requires action from a qualified person. Only that person is then allowed to reset it. Restricting the reset keeps that action with the person qualified to deal with the fault.

Data Visualization

The screens showing all or part of a process are what most people picture as SCADA. Their visual displays let an operator view the system’s data and control the process.

Data visualization displays a stream of data in a form the operator can read. Trends and charts often show how a value changes, while tables and color indicate a discrete variable’s state. SCADA has used color extensively. Standards such as ISA-101 and ISA-112 introduced the terms “grey is good” and high performance HMI.

HTML5 is an emerging technology for developing screens and visualizations. I see three main reasons for its use:

Fast Development
Easy to Access
Many Developers

HTML5 lets you prototype screens and visualizations quickly, speeding up development. HTML5 is also easy to access, particularly with responsive designs. Browsers can display HTML5 on computers as well as devices such as smartphones and tablets, so the visualizations are accessible on those devices.

Data Analytics and Machine Learning

Analyzing data is an increasing part of SCADA’s work alongside displaying it. Data analytics and machine learning belong to the Industry 4.0 revolution and make the SCADA system smarter.

Data analysis has been part of SCADA throughout its history. Most systems generate reports containing production, process and system data. People have often analyzed those reports to optimize production or maintenance.

Machine learning algorithms can work through that data and learn its patterns. They may find ways to optimize operations that human analysis misses.

SCADA Applications: Where do we use SCADA Systems?

SCADA applications range from small units to large plants and enterprises with several sites. Monitoring collects data throughout automation, which can help reduce production costs and maintenance costs while improving production efficiency. SCADA supplies the data needed for that analysis.

Improve equipment performance
Higher quality product
Reduce maintenance cost

Across many industries, SCADA monitors and controls processes. The requirements for monitoring and control differ, however, so each industry needs the system to handle the parts of its process that matter to it.

Examples of industries using SCADA for monitoring and control include:

Manufacturing
Power Plants
Water Treatment Plants (waste water)
Pharma Industry
Food and Beverages
Oil and Gas Industry
Recycling

Requirements differ between individual companies as well as industries. A large company may operate several plants, while another has a single plant or just one processing unit.

An oil and gas SCADA system may look completely different from one used for a power system or power plant.

SCADA System Examples

The examples below come from some of the largest SCADA providers. Their systems work with most PLC and control systems and use both the latest and the most widely used communication standards.

A widely used provider is often the best choice because it tends to have better support and more developers available. These systems are also often the most stable. These are reasons to consider the provider’s existing use alongside the capabilities of the software itself.

FactoryTalk View SE, Rockwell

Rockwell Automation has one of the most widely used PLC platforms. Its FactoryTalk View SCADA software is widely used too.

FactoryTalk View’s relatively low cost attracts many users. Students on a budget can use it to learn how to build and program a SCADA system without a large expense. Its cost is one reason so many people use it as a starting point for learning SCADA.

That student use also appeals to companies choosing FactoryTalk View: it means more developers already have experience with the software.

InTouch, Wonderware

From Wonderware, now owned by Schneider Electric, comes InTouch which has become one of the biggest SCADA vendors on the market. Although InTouch is fairly new to the market it is now already considered one of the best.

The Wonderware system platform combines a modular design with many “plug-and-play” components. This makes it flexible, so you can customize the SCADA system to your needs fairly easily.

InTouch also works with most PLC platforms because it uses open communication standards.

Citect SCADA, Schneider Electric

Schneider Electric also has their own SCADA software. Or had should I say. Because after they bought Wonderware, that became their primary SCADA solution and they basically stopped developing further on the Citect SCADA. Or almost at least.

Citect SCADA remains widely used, so SCADA developers need familiarity with it. It has also become a part of the Wonderware SCADA solutions.

Citect’s large user base means Schneider Electric needs to continue developing it. The system has accumulated many features over its long history, often in response to user requests.

https://www.youtube.com/watch?v=GsxcHJffuhM

Experion SCADA, Honeywell

Honeywell’s PLC platform is widely used, particularly in the US. The company also supplies a software platform for SCADA and HMI programming, making it a major SCADA vendor.

You can run Honeywell’s software as a stand-alone SCADA system or pair it with its PLC platforms, such as C200 and C300, and RTUs such as the ControlEgde RTU.

Honeywell optimizes its SCADA software for its own PLCs and RTUs, where it works best. It also supports other PLC platforms through standard SCADA interface drivers, including OPC drivers.

iFIX, General Electric

General Electric (GE), one of the world’s largest industrial companies, also supplies SCADA systems. Its iFIX software is a flexible option in that market.

One reason for iFIX’s flexibility is rapid screen development with HTML5. Its many drivers also let you build networked and distributed systems and exchange data with most modern PLCs. That combination lets developers work on the display screens while also connecting the devices that supply the system’s data.

Ignition, Inductive Automation

Ignition uses the new IoT architecture. I consider this SCADA system from Induction Automation a very good choice if you want support for all the Industry 4.0 standards and technologies.

Compared with many other SCADA systems, Ignition is fairly new. It uses the latest technologies and works well with most PLC platforms. Those qualities have led many companies to choose it for SCADA.

SIMATIC WinCC V7, Siemens

Siemens calls its SCADA system WinCC, a product with many years of development. The company is one of the largest suppliers in both PLC and SCADA markets, and many companies use its platform.

Siemens products tend to be expensive, but I think they provide good value. The company has developed its PLC and SCADA platforms over many years. That history has produced stable products, a requirement many companies place high on their list.

WinCC’s wide use means plenty of training material is available from Siemens, training academies and PLC training courses online. You can also find useful tutorials on YouTube.

MC Works64, Mitsubishi Electric

Mitsubishi is one of the largest vendors in Asia’s large SCADA market. Its SCADA software is called MC Works64. The product group includes MC Works64 alongside products for energy-use monitoring, historian functions and equipment control, among other uses.