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One of the most popular programming languages is a PLC programming language that most developers call ladder diagram or ladder logic. It is straightforward and simple to learn, and you can find it by checking Allen Bradley PLC training courses online.

The best thing about ladder logic is that you will find it similar to electrical relay circuit. Even if you have no insights into electrical circuits and relay control, you will be able to find a way to learn it without any additional problem.

The idea of this guide is to present you ladder logic tutorial that will allow you to learn basics on ladder diagram programming language for PLCs. Finally, you can quickly make real PLC programs in ladder logic for almost any software and industrial automation system you prefer.

What is Ladder Logic?

We have mentioned above that ladder logic is a programming language for PLC systems. People call it also a ladder diagram, but the most common name is ladder logic. We will call it that way in this particular guide.

You’re probably wondering what the reason for its name is, and it is pretty simple. Ladder logic contains rungs that will resemble like a ladder. Organizations or people that set standards for ladder logic is PLCOpen. You can check the PLCOpen organization that will provide you information of latest products and PLCs by clicking here.

If you want to start with ladder logic, you should have a foundation knowledge of other programming languages. It is important to state that ladder logic is a graphical programming language that uses graphics elements instead of text to make programs for PLCs. Experts call these graphics elements as symbols.

The best thing about it is that ladder logic symbols are similar to electrical symbols, which means that the original creation was for technicians, electricians, and people that are familiar with electronics. If you enjoy watching, looking and analysis schematics and electrical diagrams, then ladder logic is a perfect programming language for you.

How To Read Ladder Logic?

The main difference between electrical schematics and ladder logic diagrams is the way we draw them. You should have in mind that electrical schematics are horizontal, while the ladder logic diagram is vertical when it comes to drawing.

  • Simple to read – First thing that makes ladder logic more straightforward to understand than other programs is that you will notice that it is natural for the eye to go from left to right, and down to the next line. It is similar to reading. However, it implies only to people that live in countries where interpretation is from right to left.
  • You draw everything on PC – Drawing ladder logic requires a line at a time. As soon as you start adding more and more tracks (rungs), they will stack on each other, and make up something that looks similar to a ladder. Therefore, you should check a large ladder diagram that features lines that you have to scroll vertically on the screen.
  • Order of execution – It is important to mention that drawing ladder logic horizontally is essential due to the order of execution. This particular part will determine how PLC will run the program you make on ladder logic. Therefore, you have to add logic instructions that PLC will execute with ease. You should have in mind that PLC will always start at the top and perform its way down.

Relay Ladder Logic

It is essential to understand that ladder diagrams can look similar as electrical schematic due to vertical reading. Therefore, most people start to draw ladder logic diagrams that way, by building them and using electrical schematics for it. However, there are differences between schemas and ladder logic systems.

Check this particular website: https://en.wikipedia.org/wiki/Ladder_logic to learn more on ladder logic programming language.

The most significant differences between PLC and electrical control systems are:

  • PLC uses one ladder logic line and executes it before it reaches the next line.
  • Electrical systems use multiple lines that it can execute at the same time.

Basics Of Ladder Logic

The main thing that you will notice as soon as you create a new piece of ladder logic are two vertical lines. These particular connection developers call a rung, similar to on a physical ladder.

As soon as you place rungs inside the ladder logic symbols, you will be able to put numbers on each rung. That way, PLC will understand in which order to execute the logic programming. You probably know about the PLC scan cycle or scan time, which means that as soon as PLC makes scanning, it will complete the program based on vertical lines and numbers you added into the ladder.

How Does PLC Execute Ladder Logic?

Only one at a time – It is important to mention that the primary rule of ladder logic is that it can execute only one at the time. After it finishes first, it will execute the next one. Therefore, PLC will have the ability to perform one symbol at a time.

Each symbol is a form of instruction. Even though it tends to be confusing at first, you don’t have to worry, because you will be able to use it with ease after a while. You will gain logic instructions so that you can make pieces of logic. This particular piece of the PLC program will give different directions.

The first one manufacturers call examine if closed. It is conditional instruction, which means that you have to check if something is real. If you have a digital input, you will be able to examine the instructions by using internal memory in combination with an output.

  • It works as soon as the PLC scan starts; it will check a wide array of states on inputs.
  • It will write a boolean memory value for states between 0 and 1.
  • If the input is LOW, then it will set to 0
  • If the information is high, then you will see bit set to 1.