PLC Programming for Beginners: What a PLC Is and How to Learn It

What Is a PLC?

A programmable logic controller (PLC) is a tough, dependable computer built to run machines in factories, water plants, warehouses, and other industrial settings. Unlike a laptop, it is designed to survive heat, vibration, and electrical noise, and to run the same program for years without a restart.

PLCs date back to 1968, when General Motors asked suppliers for a replacement for the large banks of relays that controlled its assembly lines. Changing a relay panel meant rewiring it. A PLC lets you change the behavior of a machine by editing a program instead.

How a PLC Works

A PLC repeats a simple cycle many times every second, called the scan.

• Read inputs: it checks every connected sensor, button, and switch
• Run the program: it works through your logic using those input values
• Update outputs: it switches motors, valves, indicator lights, and other devices to match the result

Because the scan is so fast, the machine appears to respond instantly. When something goes wrong, a technician reads the program live to see which input or condition is stopping the sequence.

PLC Programming Languages

The international standard IEC 61131-3 defines the main PLC languages. You will meet these:

• Ladder diagram (ladder logic): graphical rungs that mirror relay wiring, and the most common language for beginners and maintenance work
• Function block diagram: connected blocks, popular for process and analog control
• Structured text: a text language similar to Pascal, good for math and complex logic
• Sequential function chart: steps and transitions, useful for machines that run in stages
• Instruction list: a low-level text language that is rarely used in new work

Start with ladder logic. Once it feels natural, structured text is the next language to add.

A Simple Ladder Logic Example

Picture a conveyor motor with a green Start button and a red Stop button. One rung of ladder logic handles it. The rung reads left to right: if Start is pressed, or the motor is already running, and Stop is not pressed, then the motor output turns on.

That "or the motor is already running" part is called a seal-in. It keeps the motor on after you release Start. Pressing Stop breaks the rung and the motor shuts off. Nearly every PLC course teaches this circuit first because it shows inputs, outputs, and memory in a few lines.

Common PLC Platforms

The major brands in the United States include Allen-Bradley from Rockwell Automation, programmed in Studio 5000, and Siemens, programmed in TIA Portal. Mitsubishi and Omron are also widely used. The brands differ in software and addressing, but ladder logic, timers, counters, and troubleshooting habits transfer from one to the next.

Ask local manufacturers which platform they run, then look for a program with training equipment from that vendor. Siemens credentials are covered in our Siemens SMSCP guide, and our mechatronics certifications overview compares other industry credentials.

How to Learn PLC Programming

A practical order that works for most beginners:

• Learn basic electricity: voltage, current, relays, contactors, and motor controls
• Practice ladder logic: start with start/stop circuits, timers, and counters
• Use a real or simulated controller: hands-on time is what employers test for
• Add sensors and automation concepts: analog signals, human-machine interfaces, and basic networking
• Earn a credential: a certificate, an associate degree, or a registered apprenticeship

Colleges build this sequence into their courses. Compare options in our ranking of the best PLC certificate programs, see associate degrees with PLC coursework in the best PLC training programs, or step up to the best mechatronics associate programs for broader training. If you want to be paid while you learn, read about mechatronics apprenticeships, and for remote coursework see the best online mechatronics certificate programs.

Jobs and Pay for People Who Program PLCs

PLC skills show up across many job titles. Technicians who maintain and troubleshoot automated equipment fall under BLS code 17-3024, with a national median wage of $73,900 and a top-10% wage above $109,890 (May 2025). Read the automation technician and mechatronics technician profiles for what the work involves.

Controls engineers, who design and program control systems, generally need a bachelor's degree. BLS reports a median of $122,900 for its Engineers, All Other category (May 2025), which is the closest match for many control roles. See the controls engineer profile. New to the bigger picture? Start with what mechatronics is.

PLC Programming FAQ

Sources: Wage figures from the BLS Occupational Employment and Wage Statistics, May 2025 release (SOC 17-3024 Electro-Mechanical and Mechatronics Technologists and Technicians; SOC 17-2199 Engineers, All Other). Language list per IEC 61131-3.