When compared with traditional programming, handling the programmable logic controller is different. The main reason for that is that PLCs use graphical-based programming language for implementing the automation for industrial equipment.

This particular language is Ladder Logic, and it is an essential addition for creating electrical backup generators and other automation processes in every single industry. You can find numerous input/output applications when it comes to programmable logic controllers. 

However, Ladder Logic is an intuitive way to program PLC by using a similar perspective as relay logic that engineers understand much better than IT programmers’ use. Generally, the relay control logic is known as ladder diagrams, and it uses a visual perspective instead of text coding.

Of course, you should remember that you would be able to use other languages for programmable logic controllers, including IL, SFC, FBD, and ST. In contrast, Ladder Logic is the most popular one due to its convenience and ability to transition with ease.

Check out this link: https://www.techopedia.com/definition/20292/ladder-logic to understand the importance of ladder diagram. 

It is popular because it comes with numerous benefits, including the ability for engineers to transition without any additional problem from relay logic to ladder logic. 

Since it depends on a visual perspective, you will be able to spot a circuit or rung and determine where you have an issue. 

Apart from that, since it is similar to relay control, both engineers and electricians will be able to transition with ease and start programming by using the same perspective as circuit ladder diagrams.

A Brief Guide to Ladder Logic

Even though you can find many instruction manuals when getting the proper PLC, remember that they are complicated to understand before you enroll the course that will help you learn the basics.

Of course, when you understand the basics, you can quickly improve your knowledge by using these manuals so that you can increase the overall efficiency as a PLC programmer.  

You should know that the particular instructions we wish to present to you would help you learn the basics, while you can enroll other tutorials and guides to improve the overall knowledge.

  • Relay-Type Ladder Logic Instructions

First, we have to mention the most popular and essential instructions that will help you understand this particular visual-based programming language. 

We are talking about relay instructions, and the most commonly used ones include OTE (output energized), XIO (examine if open), and XIC (examine if closed).

Generally, OTE, XIO, and XIC are something similar to normally closed and normally open contacts as well as relay coils inside the circuit. 

Remember that open contact means that the circuit is disconnected, and when you implement the trigger device by using switch or push-button, it becomes connected or closed.

At the same time, normally closed contact means that the circuit becomes disconnected or connected when you trigger a particular device. Finally, the relay coil is the electromagnetic device that allows the current to pass through it.

Remember that start and stop buttons are essential as well. Generally, stop buttons include the input wiring so that you cannot open the input unless you push the button. 

It happens due to safety reasons, so if the input fails, the motor will stop. On the other hand, the start buttons are the opposite.

Finally, if you wish to cleanse the motor from the energy, you need to push the stop button that will break the seal between the start coils and start contact inside ordinarily open contact. 

On the other hand, to bring the energy back to the motor, the idea is to push the start button, which will cause the normally open contact to close; the current will pass the circuit and seal it.

The other relay instructions you should consider include Output Unlatch (OTU) and Output Latch (OTL) that work as reset/set. Similarly, as the relay we have mentioned above, the OTL latches start when the rung becomes active. 

It will stay active until you activate Output Unlatch instructions, which will help you reset relays depending on your preferences.

  • Counters and Timers

Another instruction that you can use with Ladder Logic includes counters and timers. The main goal of these instructions is the same as their names suggest, they can count and state time in general.

The most basic instruction by using timer includes TON or Timer on Delay. It is the ability to start timing as soon as the rung becomes active. 

You can create a preset value based on the milliseconds. Then it will set the DN or Done-bit so that you can trigger other parts of automation depending on your preferences and programming.

Imagine that the timer starts as soon as the motor output is turned on. If you create a present for five minutes, it means that when the production is on for five minutes, the timer will start, which will interrupt the starting time.

Therefore, when the timer goes off, it will disable the motor start output, which will disable the timer as well.

On the other hand, when it comes to counter, the most popular and used one includes CTU or Count Up counter. As soon as we add the CTU instruction within the example above, and create a preset up to thousand, it means that you will have to reach this particular number to set the DN.

We can see that ladder logic is not that simple for beginners, but you will be able to learn more about it by being persistent along the way. 

However, the counter will start counting each time you turn on the output, and it will count up to thousand starts, which will result in becoming the light output so that you can start with maintenance and service the engine.

By Linda

Linda Green: Linda, a tech educator, offers resources for learning coding, app development, and other tech skills.