PLC Coding in 2019: Beginner’s Guide and Introduction to Programmable Logic Controller

If you are interested in learning more about the Programmable automated controller or Programmable logic controller but don’t know where or when to start, this article might be what you need, a PLC programming for beginners guide. In this article, we will talk about the introduction to PLC and PAC, the history, how they work and their components.

After reading this, you will be able to understand, know, and identify the primary components of a PAC and a PLC system, have a basic understanding of the function and purpose of programmable logic and automated controller. So, without further ado, let’s jump right into the introduction of PLC and PAC.


PLC or programmable logic controller is industrial computers with modular components that are designed to automate a customized controlling process. PLCs are sometimes used in industrial plants and factories to control the machine, pumps, fans, circuit breakers, motors, and other machinery. To further understand the purpose of programmable controllers, we need to look at the history of the PLC and PAC.


Industrial and factory automation began long before PLCs was even thought of. During the 1900s or the start of the industrial revolution, automation was customarily done by intricate electromechanical relay circuits. But the number of wires, relays, and space that is needed to make even simple automation was challenging.

Hundreds, if not thousands of relays are necessary to run and automate a factory process. And if there’s something in the logic circuitry are needed to be changed, that would be a big problem. On a basic level, the electromechanical relays work by magnetically opens or close the electrical contacts when the circuit coils of the relays are energized.

They are essential devices and still plays a big part in the automation of industrial machinery. At the start of 1968, the first programmable logic controller was first introduced to replace the complicated relay circuits in the factory and industrial plants.

The PLC and PAC were designed to make sure that the programmers, technicians, and plant engineers that are already familiar with the process can easily program the system with their logic and control schematics. Since its conception, the programmable controllers have been programmed using a series of ladder logic that is designed to copy the control circuits schematics of the older automation system.

The ladder diagram looks like a central control circuit where the power flows from left to right through the closed contacts that energize a relay coil.

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Ladder logic sample

As you all know, ladder logic is like a simple control circuitry schematic where the input sources like the push-button, switches or the proximity sensors are shown on the left side, and the outputs are displayed on the right side. The ability of the PLC and PAC to program difficult and intricate automated processes using an intuitive interface like a ladder logic made the change from relay logic to a programmable logic controller much more straightforward for programmers, technicians, and mechanics in the industry.

Although the very first PLCs have limited speed and memory capabilities, they can quickly improve through the years. The presence of programmable controllers helped simplify the implementation as well as the design of the industrial automation.

How do the programmable controllers work?

A programmable logic controller can be described as either small or big industrial computer system with modular parts designed to automate the control process of factories or industrial plants. PLCs are the one who is controlling all the modern industrial and factory automation.

There is a lot of components that make the PLC work, and most of them can be put in three categories: the processor or the CPU (central processing unit), the inputs, and the outputs. They are strong and sophisticated computers. But you can describe all the functionalities using simple terms.

The programmable controllers take data, perform various logics on these inputs in the central processing units and turns on or off the outputs based on the data the CPU analyzes.

The central processing unit monitors the input’s status like switch on, calve openly 40%, or proximity sensor off.

The CPU takes all the information that they can get from the inputs and perform the logic on these inputs.

The CPU will operate all the output logic like an open valve or turn off.

Programmable logic controller function flowchart

Let us use a familiar example to show how PLCs work, the dishwasher. A lot of dishwashers have a microprocessor that works like what is on the PLCs. The dishwashers have different inputs, outputs, and a CPU. Some of these inputs are the buttons on the front, the water sensor, as well as the door switch. Some outputs in the dishwasher include the heat elements, water valve, and the water pumps.

Click here for a thorough explanation on programming function flowchart.


You might have heard about another controller system called PAC or Programmable Automation Controller. The term was first used by the researchers at ARC in 2001 to differentiate PLC from the new, more powerful, more flexible, controller version that is starting to gain popularity in the market.

There is some disagreement about the differences between a PLC and PAC, and sometimes the terms are interchangeable. To some, PACs are a better choice when it comes to programmable controller unless the system is simple and minimizing the cost of the project is essential. The modern user interface, memory, and the extra power of PACs are what makes them have the edge over the most programmable logic controller in the market today.


Now that you have an idea or a good understanding of what they are, the history, and how this controller works It will be easy for you to decide what to focus on. The programmable logic controller is not easy to understand, but if you know what you are looking for, you can easily understand the process of how automation works, the components of the controller, as well as the importance of each element to properly conduct, maintain, and operate these controllers.