Describing PLC, SCADA, and HMI. What They Do, and How They Work Together?

PLC, SCADA, and HMI Course, play critical roles in process automation and advanced system design. A PLC is a hardware-based device, while SCADA is a system that works with the PLC. Yet, an HMI is also a system that operates in tandem with a PLC. Because a SCADA system and an HMI can perform similar activities, it’s critical to understand the distinction between them.

In this post, we’ll go through each of them and explain what they do. Additionally, we’ll go over how they interact in a unified system that governs various operations. We recommend having a cup of coffee since this will be a long read!

SCADA Systems

SCADA is not an error but an abbreviation for Supervisory Control and Data Acquisition.

As previously said, it is a system that includes both software and hardware components and is often used for two purposes:

  • Management of numerous operations from a remote or local location
  • Interaction with sensors, pumps, motors, and valves using Human-Machine Interface (HMI software).
  • Real-time data monitoring, collecting, and processing
  • Documenting the events in a file.

There isn’t a significant organization that doesn’t use SCADA systems today. These systems help save time, boost efficiency, process data more quickly and accurately, and allow accessible communication between various system sections. As a result, the SCADA design comprises two fundamental components: an RTU (Remote Terminal Unit) and a PLC (Programmable Logic Controller). A PLC is a microprocessor connecting directly with various items, such as end devices, sensors, or other production machinery.

On the other hand, a PLC is directly connected to the production machine, while the RTU, as the name says, is utilized remotely. Because of the sheer capacity of SCADA software, we can process, distribute, and display the essential data, making it more straightforward for staff to evaluate it and come up with solutions as needed. It does exactly what it says. Whenever a mistake occurs somewhere in the process, it alerts the operator, who may halt production and review the data from the SCADA system. This data may be checked using an HMI, which we will discuss later.

Where is SCADA Used?

SCADA systems, as previously stated, are typically employed in factories and industrial organizations in both the commercial and governmental sectors. They are being utilized to preserve efficiency and expedite data dissemination. This leads to quick decision-making and more efficient use of time. Because of their flexibility, SCADA systems may be employed in primary and sophisticated installations. SCADA systems are utilized in various industries, including energy, manufacturing, electricity, recycling, transportation, oil and gas, and many more.

Only some SCADA systems have been thoroughly optimized. SCADA systems, on the other hand, may assist save both money and time when combined with the skills of professional engineers.

What is PLC?

Regarding the hardware-based component of a SCADA or HMI system, we cannot ignore a PLC as a significant element. PLC is an industrial computer used for industrial automation. It stands for Programmable Logic Controller. PLCs can fluctuate in size and capability based on the firm’s needs. This robust industrial computer operates by continually monitoring the condition of input devices and making judgments regarding the operation of output devices.

The fantastic thing about PLCs is that they can control large sections of a production line and the entire line. This technology may be used to improve any manufacturing line, but the main advantage of PLCs is their repetitiveness. This computer can repeatedly replicate the operation or process while gathering important information.

How do PLCs Work?

So, how do they perform? That is, in fact, a straightforward affair. It’s essential that you’ll be astonished at how well it controls everything. An Input Scan is an initial phase in the procedure. The PLC, as the name indicates, detects the condition of all input devices connected to the PLC. Following the second stage is the Program Scan, which scans the program that the user produced and then executes it. The Output Scan is the next stage. It scans the output devices attached to the PLC and either energies or de-energizes them, as the name indicates.

Finally, housekeeping is the final stage. This is a preventive phase in which the PLC connects with internal diagnostics, programming terminals, etc. If the last step is completed properly and everything is under control, the PLC will continue again until the loop is completed.

How are PLCs Programmed?

PLCs used Logic even when they were initially introduced. Almost all PLC programming tools now can program in Ladder Logic. Ladder Logic is a conventional programming language used to simulate left-to-right circuit schematics. The program’s left side comprises input connections that may be closed or opened. When pushed, an open contact conducts current, but a closed contact stops current flow when the signal begins it.

We have output device connections on the right side, which might be actuators, solenoids, or valves. It’s usually a solenoid. When a signal arrives at the input contact, it is begun, and the condition (output) is met. The most recent invention is known as “C” programming. However, many programmers still prefer Ladder diagrams since they are easier to use and have been used for a long time.

What is HMI?

We saved HMIs for last since they are utilized to connect with Programmable Logic Controllers, and as such, the entire system is complete. Although SCADA is a remote system that communicates and collects data, HMI is a local unit that can do the same. The sole distinction, as previously stated, is that HMIs are local devices. The Human-Machine Interface (HMI) is the user interface that connects a system, device, or machine to the operator.

An HMI is a screen that allows a user to interact with a device rather than a specific piece of hardware. HMIs are also known as Operator Terminals, Local Operator Interfaces, Graphical User Interfaces, etc. If you know some of these terms (OT, LOI, and GUI), you’ve already used them. , HMIs are used to display specific data to facilitate understanding and control.

How Is It Different from SCADA?

As previously said, SCADA and HMI are almost identical yet still distinct. PLC, SCADA and HMI play a significant role in an industrial system. They do, however, work distinctly. An HMI utilizes data to graphically depict it, allowing for better comprehension and a more efficient monitoring process. On the other hand, SCADA systems are focused on control-system operations and have a sizeable data-collecting capacity. SCADA systems benefit from HMI in that they gather and record data.


As noted, PLC, SCADA and HMI training systems are here to gather and display specific data, respectively. Being an industrial computer, a PLC acts as a link between the process and its control. As a result, PLCs are frequently utilized in combination with SCADA systems and HMIs. An HMI is common in every business and even in our homes in the shape of a monitor or a tablet.

As technology advances, new types of HMI and SCADA systems emerge. The touchscreen is a classic example of advanced HMI, as it provides the operator with great flexibility. SCADA and PLCs both benefited from the expanding trends in industrial hardware. PLCs can currently execute the most complicated logical operations, but SCADA systems are significantly more adaptable and can gather massive amounts of data.

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