SCADA and HMI Concepts

In this post, I explain visualization in industrial automation including the difference between HMI and SCADA systems and the common features found in visualization applications.

This post introduces the concept of visualization in an automated control system. In the next sections, you will learn;

  • What visualization means in the context of an automated system,
  • What solutions are available for visualization,
  • What HMI and SCADA systems are,
  • The value of distributed SCADA systems

Let's start at the beginning: what is visualization in industrial automation?

What is Visualization?

Example of an Automated System

The picture above shows an example of an automated production line, taken from Rockwell Automation’s visualization product FactoryTalk View.

The operators who work on this production line need to be able to understand the status of each piece of equipment. For example, an operator may see that the palletizer has stopped building pallets of finished, packaged products. That operator needs to understand why the palletizer has stopped so that he can get the process running again — has the palletizer stopped because it is in error, because it is out of slip sheets, or because it is blocked by a finished pallet that has to be removed? Operators typically don’t have the knowledge or skills to look in the automation software so they need visualization to understand the current state of a process.

The engineers and maintenance technicians who work on this production line need to be able to read and write process values to ensure that the line continues running smoothly. The most basic commands that they may give to the process are to reset a fault and to start running again. More complex control may involve modifying the recipe for the product that is being produced to include more of a specific ingredient. Those engineers and maintenance technicians need an easy way to modify values in the control program without stopping the process or going online with the control program for the process.

Basically, automated control systems need to have a way to visualize their status and allow system users to control the process. This is true regardless of what is being manufactured, processed, assembled, or packed.

The Visualization Hierarchy

In the previous section, we established that operators need a way to interact with an automated process that allows them to understand the state of a process and to interact with the process.

Said another way, operators need an interface to the system. This interface would allow the controller to send information to the operator for status visualization and allow the operator to send information to the controller for process control.

So, what interface options are available for automated control systems?

Hardwired Interfaces

A Hardwired Interface

In the past, the most common operator interfaces were hardwired interfaces.

In a hardwired interface, several indicators and controls were connected directly to the digital and analog I/O modules of a controller.

The controller could indicate the status of a process using lights and beepers and operators could interact with the process by pressing buttons, turning selector switches, or adjusting dials and sliders.

Although hardwired interfaces were easy to understand, the amount of information that could be exchanged was limited. Hardwired interfaces are also expensive to maintain since every change to the interface requires new hardware and wiring.

Over time, industrial networking improved, and electronic interfaces became more feasible.

HMI Interfaces

An HMI Interface

In modern automated control systems, most machine-level interfaces are delivered as applications running on networked operator interface terminals. These interfaces are often referred to as HMIs, short for Human Machine Interfaces.

The use of HMIs has many advantages over hardwired interfaces;

  • An HMI can provide more granular status information to an operator since the application can have text, pictures, and animations,
  • An HMI application can be extended to provide additional controls for operators as required, such as a new button to reset a fault condition,
  • An HMI application can provide functionality that a hardwired interface cannot like logging data and viewing electronic versions of documentation for machines,
  • An HMI terminal is cheaper to install than a hardwired interface since there are fewer components and wiring involved.

SCADA Interfaces

A SCADA Interface

In larger plants with lots of production lines and machines, it is hard to understand the overall state of a process by monitoring each machine's HMI.

For this reason, most larger facilities will have a special control room that is off the plant floor. In this control room, a maintenance team monitors the status of the whole system using another type of interface called a SCADA system, short for Supervisory Control and Data Acquisition system.

In contrast to an HMI interface, which runs on a terminal and provides visualization for one controller, a SCADA interface runs on a Windows server and provides visualization for many controllers.

Trends in Visualization

As more and more manufacturing companies see the value in the data that they produce, the visualization aspect of automation becomes more important. Already HMI and SCADA interfaces have evolved from a series of buttons and lights to the central point for decision making in manufacturing plants. So, what’s next for visualization?

More Data and Integrations

Manufacturing companies want to collect and analyze the data produced by their machines that previously sat dormant in their equipment. To do this, they will rely on SCADA interfaces collecting data from controllers and storing it in a database.

To analyze this information, they rely on SCADA interfaces to retrieve the data and contextualize it in a visual and easy-to-understand way so that they can make data-driven decisions.

Adoption of Emerging Technologies

Technology is evolving quickly and manufacturers expect to be able to leverage new technologies such as mobility, virtualization, cloud computing, and VR/AR in their visualization solutions.

The idea is that these technologies will support employees to make better, faster decisions to drive business value. To meet market demands, suppliers of SCADA interfaces will start providing platforms that support key concepts like mobility, virtual reality, and cloud connections.

Features of Visualization

In the rest of this post, we’ll look at the common features that are included in HMI/SCADA interfaces.

Before we dive into the features, let’s take a minute to make sure that we understand the difference between an HMI interface and a SCADA interface.

HMI Interfaces

Rockwell Automation PanelView 5000 HMI Terminals

An HMI terminal is designed to do one thing really well. Specifically, it is designed to execute an HMI application. Once an HMI terminal is configured, then it will execute the HMI project that was downloaded to it as soon as the device is powered up.

Why would manufacturers use such a limited piece of hardware instead of a Windows-based PC?


HMI terminals run a specially constructed operating system that is less susceptible to malware than traditional operating systems like Windows. Many HMI terminals don’t need anti-virus or anti-always software installed because there is almost no risk of picking up a virus on their operating system.


Since HMI terminals are designed to be as basic as possible, their software is very reliable. HMIs can run for extended periods of time continuously, without the need to be patched or updated. When a manufacturer does decide to patch an HMI terminal, it can be done easily through the same software package that was used to create the HMI application. The same is true for backing up and restoring the HMI application. This is a big advantage since there aren’t many IT technicians maintaining systems on the plant floor.


HMI terminals are built from ruggedized hardware tested to specific global standards to ensure that they can withstand industrial environments and extreme temperatures.

In an HMI terminal, all of the mechanical parts which can break down, such as spinning hard drives, have been replaced by reliable, solid-state storage mechanisms to ensure that HMI terminals have a long life.

SCADA Interfaces

Rockwell Automation FactoryTalk View Site Edition SCADA System

A SCADA interface has more functionality than an HMI interface.

This is primarily true because most SCADA applications are built to run on Windows or another commercially available OS. Since the application runs on windows, SCADA users can also leverage other applications running on the same machine. SCADA developers can use these other applications to create custom functionality for their SCADA system such as the integration of CCTV cameras into the application.

SCADA systems also tend to be more performant than HMI terminals since they run on modern servers with modern operating systems, high-performance processors, and massive amounts of memory available. This makes SCADA applications more suitable for demanding applications like data processing and connecting to multiple controllers.

In the next sections, I will highlight some of the features provided by visualization applications. For the most part, these features are applicable to both HMI and SCADA applications. Where a feature is only applicable to one system, I will do my best to highlight that fact.

Visualization Features | Displays and Navigation

Display Hierarchy for a Visualization System

Visualization systems are made up of displays that present information to a user, allow a user to interact with a process, and allow a user to navigate between displays. A well-designed visualization system starts with a well-defined architecture of displays and easy-to-understand navigation. When designing your hierarchy of displays, you typically want to start with high-level abstract displays and allow a user to drill down to more specific displays.

For example, a process overview will display a complete overview of the manufacturing facility which may include processing, production, and packaging lines. At this level, the visualization user can see the status of each of these processes but cannot control any of the processes.

If the visualization user notices an error in the packaging process, he can click that process to drill down into a process area display. This is a mid-level display that provides users with more detailed information about a specific process such as packaging. This display will show a single line and an indication of the status of all of the equipment in that line. A change in the status of an individual piece of equipment may be indicated by a change of color of that piece of equipment. From this display, a user can typically start and stop a process and may be able to reset faults in the overall process.

To see the status of an individual piece of equipment an operator can click on the specific piece of equipment to open an equipment detail display. This is a very specific display that provides specific information about a single piece of equipment. This information may include current and historical fault information, statistical information about how the machine is performing, and settings for the machine which users can adjust.

Typically, a SCADA system will have a complete hierarchy of displays as described above. Since an HMI only provides control and information for a single machine, HMI applications usually only have a single equipment detail display along with a few utility displays.

Let’s talk about the utility pages that are typically included with a visualization system.

Utility Pages | Login Displays

As the name implies, a login display is a utility page that provides users with a way to log in to the visualization application. Users can be managed either directly in the visualization system software or can be linked to Windows Users and Groups.

Each user can be assigned different privileges within the visualization application. For example, users belonging to an operators group may only be allowed to view processes and not control them, users belonging to a supervisors group may be able to view and control operations by giving stop, start, and reset commands, and finally, users belonging to a maintenance group may be able to do view statistics and modify parameters related to the process.

Utility Pages | System Status Display

A system status display is a high-level display that shows the status of resources used in the system. This page may indicate the availability of devices in the system connected over an industrial network, the status of connections to external systems like historians, and the status of resources like PLCs, servers, and databases that are connected to the visualization system.

Utility Pages | Menu Display and Navigation

A menu display is a navigation display. The sole purpose of this display is to provide users with an entry point to the application that they can use to navigate to other displays in the visualization application.

Each display should also include a navigation bar. At a minimum, this navigation bar should let a user jump back to the menu display but ideally, the navigation bar should allow a user to quickly move through related pages and jump to utility pages as required.

A Note on Visualization Displays

Traditionally, HMI and SCADA displays were designed with a very busy look and feel. That’s generally because they were created by engineers who wanted to cram as much data into a single display as possible.

Unfortunately, this type of design does not help operators to understand what is happening in a process. The excessive use of colors makes it hard for operators to understand where an abnormal situation is occurring. Excessive use of animations is a constant source of distractions for people trying to understand the process. Excessive data on a single display makes it hard for operators to understand what data is important.

Thankfully, the industry has introduced some best practices that most visualization developers follow. Modern displays limit the amount of information shown to what is immediately obvious and tend to show most equipment in shades of grey when they are in normal states and only use color or animations to highlight abnormal situations.

These best practices are captured in the ISA-101 Standards.

HMI Features: Alarming

A visualization system’s primary function is to alert operators to abnormal situations. A SCADA or HMI alerts operators by raising alarms, which are audible or visible indications for operators.

An Alarm Summary Screen in Studio 5000 View Designer

Alarms are displayed on a dedicated display called an Alarm Summary display. In this display, operators can interact with alarms by acknowledging them, resetting them, and performing other actions.

The ISA 18.2 standard “Management of Alarm Systems For The Process Industries” defines the possible types of alarms and general guidelines for handling alarms in an automated control system.

HMI Features: Trending and Data Logging

A Trend Display for a Visualization System

A central feature of a visualization system is the ability to store and display tag values.

Storage of tag values is covered by data logging, which as the name implies, is the ability to log values of tags to a data log file in the controller or visualization system. Stored data can then be displayed on the visualization system as a trend.

A trend is a graph made up of data points in a time series. Trends allow operators to display and compare the values of tags of time, like in the image above.

When a trend is reading and displaying values directly from a controller, it is called a “real-time trend”.

Another type of trend is a “historical trend”. With a historical trend, the data which is displayed is read from a data log file stored in the visualization system’s memory.

HMI Features: Recipe Management

Recipe Management for a Visualization System

Recipes are sets of related parameters and values that are used to make a product.

For example, the automated control system for a bakery may support several different recipes that are used to produce different types of bread. Each recipe has different values for the oven temperature or cook times. Each recipe may also include the ingredients required for a specific recipe, like milk, eggs, and flour, as well as the required quantity of those ingredients.

These recipes can be managed through a visualization system. Most visualization systems come with a built-in recipe management mechanism that allows operators to view, select, and activate specific recipes. These mechanisms also allow certain users to modify recipes directly in the visualization application.

HMI Features: Language Switching

Language Switching for a Visualization System

The ability to sell machines and compete globally is becoming increasingly important for OEMs. End users also want to standardize their production facilities around the world by installing the same equipment in each site.

For this reason, modern visualization systems support the ability to switch languages during runtime.

To support language switching, the visualization system developer has to provide a translation of all of the visualization texts at engineering time and provide buttons for an operator to switch language at runtime.

In this way, visualization systems can be engineered in one language and translated to another language before being deployed to another part of the world.

Wrap Up

In this post, we learned all about visualization for automated control systems.

Specifically, we learned about the difference between SCADA and HMI systems and what they are used for.

We also looked at some of the common features of visualization systems including;

  • Display and navigation
  • Alarming
  • Data logging and trending
  • Recipe management
  • Language switching

Now that you have a high-level understanding of visualization systems, you should have enough context to go out and learn how to actually develop visualization systems using visualization development applications like FactoryTalk View, Studio 5000 View Designer, or WinCC Unified.

If you’re interested in learning how to develop visualization applications, sign up to the mailing list below to be notified when we release visualization tutorials.

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