Build a Future in Automation: Learn PLC Programming from the Ground Up
Programmable Logic Controllers (PLCs) are specialized industrial computers designed to control and monitor machinery and processes in manufacturing environments. These devices are integral to modern automation systems, enabling precise, reliable operation across a wide range of industrial applications. Each PLC operates based on custom logic written by skilled professionals known as PLC programmers.
PLC programmers typically start their careers as technicians, gaining hands-on experience while gradually building expertise in programming through a mix of formal education and on-the-job training. The role demands a strong understanding of both hardware and software, as well as the ability to think critically and solve intricate logic problems. With automation expanding across industries, the demand for proficient PLC programmers continues to grow—making it a compelling career path for individuals with a technical mindset and a passion for complex systems.
Securing a position as a PLC programmer requires a strong understanding of how to write and work with PLC code. Although the subject may initially seem complex, many find it more accessible than other forms of programming due to its logical structure and practical application. In the sections that follow, we’ll outline what PLC technicians need to know to begin building their programming skills and advancing toward more specialized roles.
PLC Basics
PLCs are used in manufacturing to monitor input signals, process these as needed, and send output commands. They will often run counters and timers, and may exchange data with other plant systems like databases.
While a PLC is technically a type of computer, it differs significantly from a standard desktop machine. Its primary function is to monitor input signals—such as sensors or switches—and send commands to output modules like motors, valves, or lights. To perform this efficiently, PLCs are engineered to scan their programs in rapid, repetitive cycles, ensuring real-time responsiveness and control.
Unlike a PC, there are no other processes running in the background to slow things down, so the program executes in a very stable and predictable way. This is important in manufacturing where variations could cause problems with machine movements and sensitive processes.
1. Why PLC Programming Matters
A PLC (Programmable Logic Controller) is only as effective as the program running on it. Programming defines how the system behaves—how it responds to inputs, when it activates outputs, and how it adapts to real-world conditions. A well-designed PLC program is essential because it enables:
● Automation: Replaces manual intervention by executing tasks reliably and repeatedly.
● Consistency in Operation: Ensures that processes run the same way every time, improving product quality and reducing variation.
● Real-Time Monitoring: Continuously checks the status of inputs and outputs, making rapid decisions based on changing conditions.
● Flexibility and Scalability: Makes it easier to update, expand, or reconfigure systems as requirements evolve.
● Testing and Error Reduction: Many PLC platforms support simulation and testing tools, allowing programmers to identify and fix issues before deploying programs in a live environment.
2. What PLC Programming Looks Like
PLC programs are developed using one or more standardized languages defined in IEC 61131-3, an international standard followed by all major PLC manufacturers. This means that skills learned on one platform are often transferable to others.
The three most commonly used programming languages are:
● Ladder Logic (LD): A graphical programming method modeled after electrical relay circuits. It’s intuitive for those with an electrical background and widely used in industrial settings.
● Structured Text (ST): A high-level, text-based language similar to traditional programming languages like Pascal or C. It’s ideal for complex operations, calculations, and data handling.
● Function Block Diagram (FBD): Uses interconnected blocks to represent functions and logic. It’s well suited for process control and visualizing the flow of signals.
3. How PLC Programming Works: From Development to Deployment
PLC programs are written on a computer using software tools provided by the manufacturer. For instance, Studio 5000 and RSLogix 500 are the primary environments used for programming Allen-Bradley PLCs—one of the most widely adopted brands in North America, developed by Rockwell Automation.
Once written, the program is downloaded to the PLC, where it executes in a continuous loop known as the scan cycle. Here’s a simplified example to illustrate the life cycle of a PLC program:
Example: Box Conveyor System
● Inputs: A photoelectric sensor detects when a box is ready for loading.
● Program Logic: If the sensor is triggered and the conveyor is clear, the PLC activates the motor output.
● Outputs: The motor runs, moving the box along the conveyor.
● Monitoring and Update: The PLC constantly scans the sensor and motor status, updating its actions every few milliseconds.
If changes are needed—such as modifying the timing or adding a safety interlock—the programmer makes the adjustments on the laptop, then re-downloads the updated program to the PLC.
This tight loop of logic, responsiveness, and adaptability is what makes PLCs so powerful across a wide range of industries.
Programming Methods
A PLC is programmed using either a graphical method, (essentially, drawing the flow of logic you want to see), or by text. Typically, a PLC technician familiar with reading drawings and electrical schematics will find the graphical approach easier to pick up.
The two graphical methods are ladder logic and function block diagrams. Ladder logic is the most widely used, and is an approach someone with good electrical knowledge can quickly start to understand.
A program written in ladder logic looks like the rungs of a ladder between two uprights. Each “rung” is a separate instruction, telling the PLC to do things like “Read input #64” or “Set output #16 high”.
Function block diagrams are a little less intuitive for someone with an electrical background, but are still straightforward to follow.
Text-based PLC programming, using either the structured text or instruction list methods, is arguably faster to program in, and more powerful in terms of its ability to incorporate complex functions and logic. A PLC technician familiar with programming in a language like Python will probably pick it up quickly, but those from a more hands-on background often prefer the graphical methods.
Skills and Aptitudes for a PLC Programmer
Successful PLC programmers share some common traits. They think logically and enjoy solving problems. They have good attention to detail, and they have a strong interest in electronics and mechanics.
Communication skills are also important. A PLC programmer must be able to extract requirements from people who don’t understand programming and turn them into a specification and code. They should also be able to explain what they need to do to achieve an objective, and what they need other people to do too.
How to Develop PLC Programming Skills
1. Start with the Fundamentals
Begin by learning the core principles of PLC programming, particularly the IEC 61131-3 standard languages like Ladder Logic, Structured Text, and Function Block Diagram. Formal courses—online or classroom-based—can provide essential training in logic structure, sequencing, timers, counters, and program scan cycles. A solid grasp of these basics is critical before tackling real-world systems.
2. Useful Backgrounds and Skills
While not mandatory, certain skills and experience can make learning PLC programming easier:
● Basic electrical knowledge – Understanding circuits and control wiring.
● Analytical thinking – For diagnosing and solving logic-related issues.
● Familiarity with industrial systems – Knowing how machinery and processes operate.
● Safety awareness – Understanding how to work safely with electrical and automated equipment.
Many PLC programmers come from electrical or maintenance backgrounds, while others start on the mechanical side, working with equipment setup and troubleshooting.
3. Learn by Doing
The most effective way to grow as a PLC programmer is through hands-on experience. Start by assisting with small tasks like editing code or debugging faults, ideally under the supervision of an experienced technician. Over time, you’ll progress to more complex programming projects, applying what you’ve learned in practical settings. This combination of structured learning and real-world practice builds both competence and confidence.
Where to Find PLC Classes
If you're ready to build in-demand skills and take the next step in your technical career, George Brown College’s PLC Technician Certificate Program offers a practical, industry-focused pathway. These programs are designed to equip you with the knowledge and tools needed to work confidently with PLC systems in manufacturing environments. Start your journey today. Visit the PLC Technician website or call toll-free at 1-888-553-5333 to learn more and enroll.