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PLC Training For Beginners – Part 1 of 4: PLC Basics

Welcome to our PLC training for beginners! It is the perfect place to start your journey into the industrial automation world. 

PLC Training For Beginners Part 1

This training is structured into four parts.

Part 1 - PLC Basics
  • History of the PLC
  • PLC Architecture
  • Rockwell automation PLCs
Part 2 - PLC Hardware Components
  • Central Processing Unit- CPU
  • Power Supply
  • Digital And Analog IO
  • Communication
  • Choose suitable PLC hardware for your application
Part 3 - PLC Programming
  • Studio 5000 Introduction
  • Studio 5000 Installation and Activation
  • Get Started with Studio 5000
  • Ladder Diagram Basic Instructions
  • IO Configuration
Part 4 - PLC practical training
  • Let’s develop a basic program…
  • Configure the controller in Studio5000 
  • Download logic to the controller

Though this is general PLC training for beginners, we will be focused on Rockwell automation PLCs and software in the examples.

Part 1: PLC Basics

The programmable logic controller, as shown in figure 1, otherwise known as the PLC, is a compact industrial computer designed to control system processes from one location.

Other definitions define it as a special purpose computer with no display, keyboard, printer, or hard drive. It usually hides in the control panel on the factory floor or as a digital computer used to control machinery by constantly monitoring inputs and output devices.

Thus whenever there is a need to control devices either locally, distributed, or remotely located, the PLC is the go-to solution for a flexible way to tie every component in the control system together.

PLC Components
Figure 1: Typical Programmable Logic Controller (PLC)

The PLC is a computer means it shares similar features and capabilities with typical everyday computers, such as a central processing unit, input units, output units, software, memory units, and communication abilities. 

The PLC is mainly divided into three core areas

  • The central processing unit
  • The power pack and rack 
  • The Input/output (IO) unit

History of the PLC

Prior to the emergence of the PLC, industrial control was mainly done with hardwired relays and timers, where large banks of hardwired relays and timers, which took up large amounts of space, were used to control a single machine.

The relay needed to be wired according to a defined logic for the machine to function consistently.

When one amongst the swaths of relays malfunctions, as they were always prone to do, the entire system would be shut down, and troubleshooting the problem could take hours or even days to diagnose and correct.

Relay Based Control System
Figure 2: Hardwired relays and timers

Unfortunately, this posed a great challenge, as the hardwired system wasn’t very flexible with respect to the need for change and thus slowed down optimization endeavors.

The emergence of the PLC in the ’60s, specifically in 1968, revolutionized the industrial sphere, as it meant that a single device could replace the banks of hardwired relays and timers that the industry had gotten accustomed to.

The evolution of the PLC, starting from the days of the standard machine controller introduced by MODICON in 1968 to the 084 model in 1969, the 1774 PLC family introduced by Allen Bradley in 1970, the MODICON 184 model in 1971, the emergence of the Profibus/Ethernet in the ’90s.

There is evidence that the technology has grown in leaps and bounds and still has open possibilities for further growth, thanks to technological advancements such as artificial intelligence, analytics, machine health monitoring systems, and optimization.

PLCs are now offered in different sizes, dependent on the application of usage. It is not unheard of to see a pocket-size PLC, which could be used for limited control purposes, while larger ones are most applicable for larger and more complex control applications.

PLC Architecture

Figure 3 depicts the overall architecture for a typical PLC connection with direct connections to the actuators, communication modules, Input and output modules, communication channels such as the Profibus, analog sensors, etc.

Different protocols guide communication within a PLC network: Profibus, Modbus RTU, Devicenet, EthernetIP, Hart, ModbusTCP, and Profinet.

PLC Architecture
Figure 3: Architecture for a typical PLC

The main components of a PLC hardware consist of a programming device, input and output modules, power supply, and the central processing unit.

Its software consists of the diverse distinct manufacturer software development platforms used for programming the PLC, using different languages such as structured text, ladder logic, and function blocks.

In part 2, we will focus on every component in detail.

Rockwell automation PLCs

There are dozens of different PLCs vendors, but as mentioned at the beginning of the training, we will focus on Rockwell automation PLC.
The reason for picking Rockwell automation PLC is that it’s the most common brand in the USA and a leading vendor worldwide.

Although we at PLCynergy are familiar with all the leading PLC vendors, we are experts in Rockwell automation PLCs and software.


ControlLogix is Rockwells flagship controllers family, also recognized with the catalog number 1756. It’s not a specific PLC rather a family of related hardware built around the L6X-L8X CPUs.

ControlLogix 1756
Figure 4: ControlLogix Controllers

The ControlLogix family includes CPUs, Power Supply, Rack, IO Modules, Communication Modules, and all hardware required to implement a redundant system if needed.

The ControlLogix is a high-performance PLC series with a modular and rack-based architecture allowing flexibility and scalability. Therefore more appropriate for large-scale applications.

The PLC programming software of the ControlLogix series is Studio5000 or RSLogix5000 (For firmware less than V20). Those softwares are practically the same. Studio5000 is just a new branding for the RSLogix5000.

To summarize, It’s the PLC with the best capabilities you will ever find in the market, and its price is accordingly.


The CompactLogix family is an excellent PLC series, also recognized with catalog number 1769 or 5069.

CompactLogix1769 5069
Figure 5: CompactLogix Controllers

The CompactLogix family is also modular but has few models integrated with a power supply, IOs, and communication in one box. Therefore it is more suitable for small to medium applications.

Studio5000 or RSLogix5000 are the programming software also for CompactLogix. The support of two different PLC families is very beneficial to the organization that holds ControlLogix and CompactLogix on the plant floor.

To summarize, CompactLogix is a perfect PLC for a single machine or production line, and it’s much more affordable than ControlLogix.


MicroLogix is a pretty old PLCs family. Part of the family doesn’t manufacture anymore. The only two PLCs still active is the MicroLogix 1400,1100.

Figure 6: MicroLogix Controllers

The MicroLogix is an excellent choice for small applications since it has an integrated power supply, built-in IO with an option to extend with additional IO modules, and communication ports.

It’s worth mentioning that the MicroLogix 1400 and 1100 have an Ethernet port that supports both EthernetIP and ModbusTCP protocols. And also RS485 serial ports for older protocols like DF1 and Modbus RTU/ASCI.

The prices of the MicroLogixs are low compared with the other Rockell PLCs and compared to competitors’ PLCs.

The programming software of this PLCs family is RSLogix500.

To summarize, MicroLogix is an old PLC series, but it is still active and manufactured today. We love using it in tiny projects with a tight budget or even as a communication gateway.

MicroLogixs PLCs had their time, and their use has reduced in the last few years. Rockwell seems to develop the next PLCs family (Micro800) to replace the MicroLogixs in the future.


Micro800 is the heir of MicroLogix. It has almost the same features include support in different serial and ethernet protocols.

Figure 7: Micro800 Controllers

The Micro800 is more affordable than the MicroLogix, so there is no sense in choosing MicroLogix over Micro800.

The programming software for this PLCs family is CCW – Connected Components Workbench, and it’s free in its standard version. The Pro version is pretty cheap and supports online edits.

And the old ones PLC5, SLC.

Nowadays, it is hard to find a PLC5 in a production environment. Although it is a work-horse PLC, it respectfully represented the Rockwell automation brand for a few decades.

The ControlLogix replace the PLC5 family in the late ’90s.

SLC500 is the middle-range PLC family of the past, and the CompactLogix family has replaced it.

Figure 8: PLC5 and SLC500 Controllers

final thoughts

Programmable logic controllers (PLC) offer a flexible way to effect control action. The ability to handle complex applications makes a must-have for critical operations such as manufacturing, distributed control applications, remote control applications, and adaptive control applications.

Its strength comes from the fact that it is programmable and thus allows for quick changes to program logic in record time, unlike the previous hardwires relay and timer logic.

The PLC has come a long way indeed, as it revolutionized industrial control, and with the emergence of more advanced technologies and techniques, we can rest assured that the PLC is here to stay for good.

Whats Now

Congrats! You finished the first part of our PLC training. The next part of this training is PLC Training For Beginners – Part 2 of 4: PLC Hardware Components. In this part, we will dive in and specify the hardware parts of a PLC.

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Check out our new course:

PLC Programming

with Studio 5000 Logix Designer

Check out our new course: