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How SCADA, HMI, and PLC Work Together

By Telstar Inc |

In a world that’s continually getting more efficient, it’s not a surprise to find that most of the conveniences we take for granted are completed through automated processing. With minimal attention needed from human operators, machines are doing important work like analyzing data, performing actions, and working cohesively alongside each other.

Thanks to the progression of industrial automation, systems like SCADA and components like PLCs and HMIs were put together to increase productivity, boost convenience, and improve safety against hazardous conditions.

Today, hundreds of significant facilities use SCADA and PLC systems, which almost always have HMIs. These processes are crucial when it comes to processing automation and advanced system designs. These systems are only going to improve. The use of SCADA is expected to grow by nearly 7 percent by 2024, with more manufacturers adopting this more productive method.

But since some of these systems have similar features and functions, it’s essential to know how they differ and function specifically for your industry needs.

A Quick Breakdown of SCADA, HMI, and PLC

SCADA systems are necessary for industrial automation function. Like a computer, these complex systems can analyze information, record data, and perform tasks without much human assistance.


Supervisory Control and Data Acquisition (or SCADA) is an automated control process that many large industries use for industrial automation, such as manufacturing, construction, and engineering facilities.

SCADA is a system made up of two components:

  • PLC (programmable logic control)
  • RTU (remote terminal unit)

Often, SCADA will also have a separate component called HMI (human-machine interface). Altogether, SCADA is a system that has software and hardware elements used to control processes, interactions, and monitor and record data through PLCs and HMIs.


A human-machine interface is a user interface or dashboard that allows the human operator to interact with a machine. HMIs are used all over the world in various technologies, ranging from smartphones to power plants.

HMIs are not part of a particular software but is used for people to communicate with a machine or device. Mainly, HMIs help users understand and control data with the touch of their fingertips through communicable devices, such as:

  • Screens
  • Buttons
  • Levers
  • Computer mouse
  • Keyboards

SCADA systems can function without an HMI, although having one is often recommended. This way, the operator can understand how to communicate with the system and receive any error notices that need to be addressed.


A programmable logic controller is often described as a mini-computer that can communicate with different objects, systems, and machines. They are designed to control and troubleshoot networks, which is why they are necessary components to SCADA.

PLC Diagram

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This system simplifies machine usage while also providing necessary functions, and are used for any situation that requires high-reliability control by a human operator. Plus, they are an intricate part of industrial automation, and SCADA systems cannot function without them.

Some primary functions of PLCs within SCADA include:

  • Robots
  • Assembly lines
  • Counters
  • Measurements
  • Calculations
  • Sensors
  • Motors
  • Lights
  • Fans
  • Circuit breakers

The Important Role of Industrial Automation

Industrial automation is the use of several control systems for operating machinery and equipment. This ranges vastly between several types of industries, like manufacturing factories and control systems for buildings, transportation, and communication.

This type of process is high-functioning and uses computers and machines to replace humans for work, requiring minimal attention from the human operator. Because of this, some of the main advantages of an automated system include:

  • Increased productivity since machines can operate tirelessly
  • Product quality improvement with the same output each time
  • Cheaper labor costs by replacing workers with machines
  • Reduced routine checks with PLCs and HMIs working together
  • Raises the level of safety by taking workers out of hazardous environments

Ultimately, automation is an excellent way to do significant procedures with minimal human intervention. And although used in different forms, this method has been utilized by humans for centuries.

A Brief History of Automation

Although Ford Motor Co. coined the word “automation” in 1948, the process can be traced back to Ancient Egypt. In fact, one of the earliest feedback-controlled mechanisms dates back to 270 B.C.!

For the next several centuries, humans have been finding ways to make work easier. With harvesting food, building houses, and the introduction of the Industrial Revolution, there were hundreds of ways to make life more functional. Throughout the 1800s, people experienced the very first self-operating machines, such as furnaces, engines, and temperature regulators.

As time leaped into the 20th century, and people heavily utilized electricity, industrial automation came into full swing. Slightly more complex than the automation people had known for years, industrial automation was the control and use of various systems for operating equipment like machinery.

Today, there is a high demand for products, supplies, and necessities like transportation and power production. One of the easiest ways to meet these demands is by using industrial automation. These complete systems help control these major parts of life, which all require effective systems like SCADA, PLCs, and HMIs.

How Do SCADA, HMI, and PLC Work Together in Industrial Automation?

In today’s world, there is so much technology to keep up with. So although understanding exactly how complex systems like SCADA works might sound overwhelming, it’s a straightforward chain of information. Remember, SCADA systems are intended to:

  • Automate processes and procedures
  • Track and analyze data and errors
  • Perform remote site monitoring
  • Increase productivity and guarantee same-quality outputs

But how do SCADA, PLC, and HMI work together?

SCADA is most easily understood as the central database that stores and controls your operations at large. This communicates with the PLC, which is how the system functions and communicates within the operational environment. If there is an HMI, it might come in the form of a screen, buttons, levers, or a keyboard, thus allowing humans to interact with the SCADA-PLC system. Some examples include factory machines, computers, and vehicles.

What is SCADA 1

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In industrial manufacturing, HMIs are essential in delivering information to the operator. The PLC system can identify any issues within the SCADA system, and through the HMI, present it to the human operator so the problem can be fixed.

Manufacturing Facilities

Did you know that the U.S. exports nearly half of all manufactured goods to countries with free-trade agreements? Made up of 20 countries, including much of South America and Canada, the U.S. is the number one resource for exporting goods. Plus, the U.S. also supplies 34% of products to the rest of the world.

There is an endless number of industries which use automation systems, but some of the most popular ones are:

  • Food, such as livestock, grains, fruit and vegetable preserves, and packaging
  • Beverage and tobacco, like bottled water, soda, alcohol, cigarettes, and cigars
  • Textiles, like fabrics for apparels, bedding, towels, curtains, and more
  • Wood products, like lumber, plywood, veneer, flooring, and home-building materials

It’s safe to say that there is a need for goods around the world, which in turn also means that productivity demands are higher than ever. To help meet these demands, manufacturing facilities turn to industrial automation systems, which help expedite the productivity and consistently produce high-quality products.

Power Production

With power usage growing steadily in countries across the world, there is a major need for automatic power production. Although these facilities require human operators, a lot more output gets distributed thanks to automation systems like SCADA.

Food and Retail

If you have been to a McDonald’s fast-food restaurant lately, then you might notice a new addition to their stores: an ordering kiosk. With this automatic touch screen ordering system, productivity is enhanced, which means less waiting time for consumers and more time to focus on work for employees.

But McDonald’s isn’t the only one utilizing automated systems. In any given restaurant or grocery store, you might find examples of these systems, such as:

  • Conveyor belt systems
  • Online shopping options
  • Self-checkout machines
  • Drone deliveries

Another prime example of SCADA systems within the retail industry is automatic banking. Thanks to ATMs, people are able to obtain cash from their checking accounts anytime. These systems use SCADA, PLCs, and HMIs to work collectively.

Travel and Traffic Systems

Operators heavily rely on automatic systems when controlling and monitoring transportation procedures, such as:

  • Airplanes
  • Air traffic control
  • Steering ships
  • Trains
  • Mechanical lane changes
  • GPS trackers and devices
  • Scheduled lights at intersections

Operators will use the human-machine interface, which can be a combination of screens, levers, buttons, and keyboards.


Industrial automation is changing the way the world works. More than ever before, machines can operate and process data to expedite productivity, lower labor costs, and require less human interaction so that output is consistent.

Almost every large organization depends on SCADA systems. If your facility needs to meet the demands of your customers, then it might be time to consult with Telstar Instruments. We will help you design the system, address your exact needs, and always stay within a budget for the best way to utilize our state-of-the-art SCADA and PLC systems.

Contact us today for more information on our Telstar instruments!