PLC Programmers Using Online Tutorials: Introduction to PLC

If you have been wanting to start a career in industrial automation and have been looking for basic Programmable Logic Controller training, but don’t know where or how to start, then this article is an excellent way to start. PLC or Programmable Logic Controller is a small industrial computer with modular parts perfectly designed to automate a customized control process. 

This system is usually used in industrial plants and factories to help control circuit breakers, lights, fans, pumps, motors, and other small to large machinery. To help people understand the purpose of this system a lot better, let us take a look at the brief history of Programmable Logic Controller.


Automation in the industrial setting began before PLCs. In the early 1900s to 1950s, automation was usually done using complex electromechanical relay circuits. But the amount of space, wires, and relays needed to create simple automation was pretty problematic. A lot of relays are required in order to automate a simple industrial factory process. And if something went wrong in the logical circuit, the changes needed are quite problematic. 


Visit to find out more how relays work.


People should note that on a basic level, electromechanical relays operate by magnetically closing or opening the electrical contacts when coils of the relay are powered or energized. These relays are very useful and still plays a significant role in the industrial automation process. In 1969, the very first PLC came along to replace complex relay circuitries in industrial plants. 

The system was designed to help technicians and plant engineers to program the entire plant machinery with ease using control schematics and relay logics that they are already familiar with. Since its inception, PLCs have been programmable using specific ladder logic. It was designed to imitate control circuit schematics. These ladder diagrams look like common control circuits where power is flowing freely from left to right through different closed contacts to help energize relay coils.

As you can see, these ladder logics are like common control circuit schematics. It input sources like proximity sensors, switches or push-buttons, and are usually shown on the left. The outputs are shown on the right side of schematics. 

The ability to program complex automated processes with the help of intuitive interfaces like ladder logics made transitions from relay logic to Programmable Logic Controllers a lot simpler for a lot of industries that needed automation. 

The system’s ability to program complex automated processes using an intuitive interface made the transition from the traditional relay logic system to Programmable Logic Controllers a lot easier for most industries. Although early PLCs were limited when it comes to their speed and memory capabilities, the system quickly improved as the years go by. The presence of these controllers helped simplify the implementation and design of industrial automation. 

How does this system work?

The Programmable Logic Controller can be described as a small industrial computer with modular parts designed to help automate the control process of a factory or industrial plant. These systems are the controllers behind most, if not all, modern industrial automation. There are a lot of parts to this process, but most of them can be put in these three categories:

Central Processing Unit or Processors



These systems are pretty powerful and sophisticated computers. Without proper PLC training, these complex computers can be very difficult to operate. However, we can describe the function of the logic controller in simple terms. The controller takes inputs, performs different logics on these inputs in the Central Processing Unit, and turns on or off outputs based on that logic. 

The Central Processing Unit monitors the status of the system’s inputs (valve 40% open, proximity sensor off, or switch on).

It takes the information that it receives from every input, performs logic on the data.

It operates the output logics like turning off the motors or opening the valves.

Programmable Logic Controller or Programmable Automation Controller

People might know about PAC or Programmable Automation Controller. It was first coined by market research firms in 2001 to help differentiate the original Logic Controller from the more flexible, more powerful, and newer controllers that were starting to emerge in the market. 

There are a lot of disagreements about the differences between PLCs and PACs. Because of these disagreements, people in the industry usually interchange the use of these terms. According to most experts, PACs are the better choice unless the system is simple, and minimizing the project cost is very important. The modern user interface, memory, and the extra power of these PACs make them a much superior system compared to PLCs.

One of the leaders in industrial automation, Allen-Bradley, was actually phasing out some of their PLC lines like PLC-5 and started focusing on their PACs. According to experts, it is an excellent move. Some of PACS are far superior compared to traditional PLCs when it comes to programming software and performance. 

Having experience using both PACs and PLCs is vital for people interested in engaging in industrial automation. But PACs are considered as the future of automation. It is where industrial automation engineers and technicians spend most of their time. 


When dealing with this process, people need to know the history behind the system. Both PLCs and PACs are critical in the everyday operation of different industries. Automation is the future of every industry; that is why it is best to get ahead of your competition. Take time to study every little detail when it comes to automation.