PLC Programming Languages

In summary, PLC programming languages are basically of two types: Textual languages and Graphical languages. There are 5 programming languages under those categories:

1. Structured Text (ST)

2. Instruction List (IL)

3. Ladder Diagram (LD)

4. Function Block Diagram (FBD)

5. Sequential Function Chart (SFC) 

The first 2 are Textual languages and the other 3 are Graphical languages.

Now, let's discuss the above PLC programming languages in detail.

Introduction 

If you've ever wondered how complex industrial processes are automated, the answer lies in Programmable Logic Controllers (PLCs). These robust electronic devices have revolutionized industries by providing a reliable and efficient means of controlling machinery and processes. 

At the heart of PLC programming lies a range of specialized programming languages that enable engineers and technicians to communicate with these powerful controllers. 

In this article, we'll explore different types of PLC programming languages, their significance, and how to choose the right one for your automation needs.

What is a PLC?

A Programmable Logic Controller (PLC) is a digital computer used to control and automate industrial processes. PLCs are widely used in manufacturing plants, power stations, water treatment facilities, and various other applications that require precise control and monitoring. 

These devices are designed to withstand harsh environments, making them ideal for industrial automation.

Importance of PLC Programming Languages

PLC programming languages serve as the interface between human operators and the PLC hardware. 

They allow engineers to develop logic programs that dictate the behavior of the PLC. The choice of programming language directly impacts the automation system's efficiency, readability, and maintainability. 

It is crucial to select the appropriate programming language based on the specific application requirements and the skillset of the programmer.

5 Common PLC Programming Languages

1. Structured Text (ST)

Structured Text (ST) is a high-level programming language that resembles Pascal or C programming. It allows for complex calculations, data manipulation, and advanced control algorithms. 

ST is often preferred for applications requiring extensive mathematical computations or complex data structures.

2. Instruction List (IL)

Instruction List (IL) is a low-level programming language that resembles assembly language. 

It provides direct control over the PLC's internal operations and is often used in performance-critical applications or when optimizing code execution speed is crucial.

3. Ladder Logic

Ladder Logic is the most widely used programming language in the world of PLCs. It derives its name from the ladder-like diagram representation, resembling electrical relay circuits. 

Ladder Logic is intuitive and easy to understand, making it an excellent choice for beginners. It is particularly suitable for discrete control applications.

4. Function Block Diagram (FBD)

Function Block Diagram (FBD) is a graphical programming language that uses interconnected blocks to represent functions and operations. 

It is ideal for visualizing complex control systems and is often used in applications with multiple parallel processes.

5. Sequential Function Chart (SFC)

Sequential Function Chart (SFC) is a graphical programming language that enables the description of sequential processes. 

It is particularly suitable for applications with complex sequences of operations or state-based control systems.

 

Advantages and Disadvantages of Different PLC Programming Languages

Let's examine the pros and cons of the most commonly used PLC programming languages:

Structured Text (ST)

Advantages:

- Supports complex calculations and data manipulation.

- Resembles high-level programming languages.

- Ideal for applications with advanced control algorithms.

Disadvantages:

- Steeper learning curve for beginners.

- Requires a good understanding of programming concepts.

Instruction List (IL)

Advantages:

- Provides direct control over the PLC's internal operations.

- Optimizes code execution speed.

- Suitable for performance-critical applications.

Disadvantages:

- Difficult to read and understand.

- Limited readability and maintainability.

Ladder Logic

Advantages:

- Easy to understand and learn.

- Graphical representation resembles electrical circuits.

- Well-suited for discrete control applications.

Disadvantages:

- Limited capabilities for complex calculations.

- Not suitable for handling large amounts of data.

Function Block Diagram (FBD)

Advantages:

- Visual representation of interconnected blocks simplifies complex control systems.

- Easy to understand and modify.

- Suitable for applications with parallel processes.

Disadvantages:

- Limited availability of FBD programming resources.

- May not be the best choice for small-scale applications.

Sequential Function Chart (SFC)

Advantages:

- Enables graphical representation of sequential processes.

- Supports state-based control systems.

- Easy to visualize complex control sequences.

Disadvantages:

- Not suitable for all types of control applications.

- Requires careful design to avoid excessive complexity.

Choosing the Right PLC Programming Language

When selecting a PLC programming language, several factors should be considered:

Application Requirements

The nature of the automation application plays a vital role in determining the suitable programming language. 

For example, discrete control applications are well-suited for Ladder Logic, while complex calculations may require Structured Text (ST).

Programmer's Skillset

The expertise of the programmer should be taken into account. If the programmer is proficient in a particular programming language, it may be more efficient to use that language for development and troubleshooting.

Industry Standards

In some industries, specific programming languages may be favored due to standardization or compatibility reasons. It is essential to consider industry guidelines and regulations when choosing a PLC programming language.

Conclusion

PLC programming languages form the backbone of automation systems, enabling precise control over industrial processes. By understanding the characteristics and advantages of different programming languages, you can make informed decisions when developing automation solutions. 

FAQs

FAQ 1: Can I use multiple programming languages in the same PLC?

Yes, some PLCs support multiple programming languages. This can be useful when different parts of an application require specific language features or when integrating existing code written in different languages.

FAQ 2: Is there any free PLC programming software available?

Yes, some manufacturers offer free versions of their PLC programming software, allowing users to practice and develop programs without the need for expensive licenses. However, advanced features may be limited in the free versions.

FAQ 3: Can I convert programs written in one language to another?

In some cases, it is possible to convert programs between PLC programming languages using software tools or manual rewriting. However, the level of automation and ease of conversion may vary depending on the complexity and structure of the original program.

FAQ 4: Which programming language is best for beginners?

Ladder Logic is often recommended for beginners due to its graphical representation and simplicity. However, it is essential to consider the specific application requirements and industry standards when choosing a programming language.

FAQ 5: How can I keep up with the latest trends in PLC programming languages?

To stay updated with the latest trends in PLC programming languages, follow industry publications, attend conferences and webinars, and engage in online communities dedicated to automation and PLC programming. 

Regularly exploring the manufacturer's resources and software updates can also provide insights into new features and capabilities.

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4 Industrial Automation Certifications You Must Know

Today competition is in every field has increased a lot and to be different from other employees, we have to do different things. There are certification in every field and to get good recognition gaining certification is very important. Not only it increases competency but also gives professional recognition. So today in this post we have listed some industrial automation certification, which will help you in boosting your knowledge and career. Subscribe to Automation-Talk by Email.

4 Industrial Automation Certifications You Must Know

1. ControlLogix Certificate Program by Rockwell: Rockwell automation is a well know company in automation and their PLC's are used in every sector. So if you are a PLC programmer having experience in ControlLogix PLC's, then this certification is certainly for you. This is a self-preparatory program and you will have to follow the given syllabus.

You will complete a series of three required ControlLogix courses related to your maintenance or programming job responsibilities, plus one course elective.

To earn the ControlLogix certificate, the program requirements must be completed within 12 months. For more details please check here.


2. RSTrainer for RSLogix 5000 Software: This is another certification program by Rockwell which is a computer based training. To clear this certification you can get study material after registration and this course is available in both computer-based and web-based delivery formats and is part of a series of e-Learning courses designed to teach you RSLogix 5000 software.

Syllabus for this certification includes:

Introduction to RSLogix 5000 Software
• Installing RSLogix 5000 Software
• Identifying Main Window Components
• Configuring the Display
• Navigating through the Software
• Using Help Options

Creating and Configuring a New Project
• Creating and Managing Project Files
• Configuring a Controller
• Organizing Tasks, Programs, and Routines
• Configuring a Local I/O Module
• Organizing Data
• Producing and Consuming Tags
• Exporting and Importing Tags

Get more detail here

3. SITRAIN Certification Program: This is the certification program by Siemens and under this program, there are many certifications. This is a worldwide recognized program and the certification is valid for 3 years. Below chart shows the entry qualification for each certification.



The certifications are divided as per PLC make and model viz. Certification based on SIMATIC S7-300/-400 with STEP 7 V5.x and Certification based on SIMATIC S7-1500 with TIA Portal and there are some compulsory training which you must attend before attending these certifications. There are also certifications in the Process Automation field. Get more information here.


4. Professional Certificate of Competency in Programmable Logic Controllers (PLCs) & SCADA Systems: This certification is from Engineering Institute of Technology (EIT) which is endorsed by the International Society of Automation (ISA). This is a general purpose certification course for new learners and include basic concept of SCADA and PLC system, PLC programming (ladder logic), industrial communication protocols, PLC panel designing and much more.

Syllabus, fees and more information can be found here.

Apart from this certifications, there are many local institutes which gives you the PLC programming and SCADA training at low cost. In this program they teach about 2-3 different make PLC, SCADA, PLC programming, Electrical etc. If you know any other industry wide automation certification, please let us know through your comments.

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Best Free PLC Simulator

While in a learning phase of ladder logic we usually don't have PLC programming software to test our logic made in paper or even you don't have a PLC software for your testing and reference. In that case, you can use some free PLC simulator which are available online. There is some site which provides students and trainer free PLC simulating software. Subscribe to Automation-Talk by Email.


 

 

Best Free PLC Simulator

1. LogixPro 500 PLC Simulator by TheLearningPit.com

LogixPro 500 is the ideal tool for learning the fundamentals of ladder logic programming. The full version of our LogixPro 500 Simulator is available for download and free evaluation. What this means is that you can download and try out LogixPro 500 in a 15 day Trial Evaluation mode, and make up your own mind as to whether it's the most advanced PLC Simulator and best training value on the market today.


Recommended Article: Best PLC Ladder Programming Books

 

2. TRiLOGI PLC Simulator software

TRiLOGI" is the name of the ladder or ladder + BASIC programming software for the Nano-10, FMD and F-series PLCs via LAN or the Internet. It can also be used for programming the legacy M-series (T100MD+ and T100MX+) PLCs, although some of features are not available to the legacy PLCs.

It is a perfect training tool for learning PLC programming. Students or technicians can quickly create a ladder logic program on their laptop and instantly test the program using the simulator. Do try it.


 

3.FREE Online PLC Simulator

plcsimulator.net provide free online PLC simulator. This PLC simulator will help you to enhance your PLC programming skills. Just visit the site and test your Ladder logic skills.

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These were some of the best PLC simulator which are available online for FREE. If we find more such PLC simulator we will update your through our Email newsletter.

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PLC Programming for Tank Level Measurement using Ultrasonic Sensor

In our earlier post, we saw the PLC Logic for Auto Filling of Tank using digital inputs for LOW and HIGH-Level signals. 

Today in this post, we will see how we can measure the level of a tank using the Ultrasonic/Capacitive level sensor and accordingly ON/OFF the PUMP at low and high levels.

 

PLC Programming for Tank Level Measurement Using Ultrasonic Sensor

First of all, we need to choose the Ultrasonic/Capacitive level sensor according to our tank level height. The sensor will give a 4-20mA signal to PLC and accordingly, we will calculate the level in the tank.

PLC Logic Development:-

Now, we need to connect the analog input from the ultrasonic sensor to PLC, we have already told that in our earlier post. You can see it here.

After that, we have to write SCL (scaling instruction) in the PLC to convert the value received by PLC to the scale we want. 

For example, if the height of our tank is 5000cm, PLC will receive the 4-20ma signal and internally will convert it into a range of o to 0FA0 (hexa), and with the help of SCL instruction we will scale this value between 0 to 5000.

So that when the Ultrasonic sensor will give 4mA signal then the level in the tank will be zero and when a signal of 20mA will be received then the level in the tank will be 5000cm.

In SCL instruction, we have to define the scaling parameters in some D:-

D200 - 0
D201 - 0
D202 -5000 (hexa)
D203- 0FA0 (hexa)

Here the value 0 to 0FA0 received by PLC will be scaled to 0 to 5000 (our tank height).

Now in this PLC Program we have kept the low level at 2500cm and the high level at 4600cm. You can download the PLC program from below, we have built the PLC Program using the Omron CX-supervisor software. Both the .cxp and .pdf files are included.

Download PLC program for Tank Level Measurement.

Hope you like this PLC program on controlling your Tank according to the measurement using an Ultrasonic sensor. If you face any problem with this PLC Program or want any modification then write us in the comment section. 

Also, you can subscribe to receive the latest updates about PLC Programming languages, SCADA tutorials, HMI programming, MODBUS programming, VFD Installation., etc. subscribe to Automation-Talk by Email.

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How to Choose your PLC or PLC Choosing Criteria

Choosing a PLC or Controller for your Process is very important as it helps in cost optimization. If you choose a wrong PLC it may happen that you are out of I/O's while programming or maybe you have the excess of I/O's left which are of no use. So it becomes very important that you choose a right PLC for your Automation Process.There are several criteria that help in choosing a PLC. Before knowing the Criteria of choosing a PLC you should know basics of PLC. Subscribe to Automation-Talk by Email.

Below are some points which will help in choosing a PLC but keep in mind that you should know exactly the need of the Customers and should know how many Input and output he wants for present and for future.

PLC are chosen generally on the basis of some requirement of the company or individual person. We should keep in mind the following below point while choosing a PLC.

Some of the PLC choosing criteria are

1. Number of I/O's:

It is very important that you know the exact number of input and output that are going to be used in the process for best and economical use.


2. Type of I/O's:

The Automation Engineer should also know the type of I/O's whether he needs a digital input like Sensor, Push Buttons etc. or an analog input like RTD, thermocouple etc. The requirement for Output should be also known as what type of Output is required whether you required a digital Output like Relay, Contactor, Lamp etc. or you need an Analog output like Drive and Control Valves.


3. Memory size of PLC:

Choosing PLC memory size is also important as you may be out of space in PLC while writing a PLC program if you choose less memory size PLC.


4. Compact or Modular PLC:

Compact Type PLC are those which has Power supply and controller in the same housing while Modular type PLC has power supply and controller in a different housing. So it is good to choose compact or Modular type PLC according to your requirement.


5. AC or DC PLC:

AC PLC's are those which are operated on 220 V i.e. they require 220 V for running. Whereas DC PLC requires only 24V for Running. So you should know which type of PLC will be good for you according to the Power Supply available in your Control Panel.


6. Sinking and Sourcing PLC:

Making a PLC source at Input or making a PLC sink at input depends upon the requirement of the user so PLC should be chosen in that way. Some PLC may support both Sink and Source at Input and Output Both.

Recommended Article: Understanding Difference Between Source & Sink in PLC's

7. PLC Scan Time:

PLC scan time is a time needed for PLC to completely Scan one cycle of PLC. It may consist of reading PLC input status, clearing PLC memory, Executing the PLC program and updating the Output. The PLC with less Scan time are found to be more Costly.


8. Number and type of Communication ports in PLC:

The number of communication Port or type of communication port is also very important in choosing a PLC. Suppose you want to communicate your PLC in MODBUS but you don't have a MODBUS port so your PLC is of no use. Also, take an example where you want to communicate an HMI with RS232 port but you don't have one. So communication Port should also be in mind while choosing a PLC.

So these were some of the Criteria for Choosing a PLC which should be kept in mind while you buy a PLC. PLC choosing criteria of Allen Bradley, ABB, Siemens, Omron, Mitsubishi, GE Fanuc, Delta, Fuji, GE or any other PLC are same in all cases. Subscribe to Automation-Talk by Email for more Tips and Tutorials.

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Best PLC Ladder Programming Books

If you are new to PLC programming or want to enhance your programming skills, then you really have to work hard. For this, you will need a good mentor and good books for your help. 

Today here we will discuss some of the good PLC Ladder Logic learning books which will help you in your Industrial Automation carrier. Subscribe to Automation-Talk by Email.

1. Programmable Logic Controllers with ControlLogix by Jon Stenerson :

Programming Controllogix Programmable Automation Controllers strength is its breadth and depth of coverage, taking the reader from an overview of the Programmable Logic Controllers through ladder logic, structured text, sequential function chart, and function block programming. 

Students learn more and more easily because of the practical coverage, numerous examples, and extensive exercises.



According to one of its reader, this book is must read for beginner with no ladder logic experience. See more Info


2. Introduction to PLCs, Second Edition by Jay F. Hooper :

This book is oriented to the people that work on and troubleshoot PLCs on the factory floor. It is directed at the actual problems and conditions that will be encountered within a realistic setting. 

The text is designed to present a clear, concise picture of how PLCs operate to the person that wishes to learn more about them.



This book takes you from the beginning of understanding to the most complex problems helping you understand every step of the way. See more Info


3.Programmable Logic Controllers Textbook with PLC Stimulation Software by Max Rabiee:

Programmable Logic Controllers emphasize the practical use of the PLC in the process and industrial control systems. The textbook begins with the basics of what a PLC is and does, then guides students through the fundamentals of programming the device. 

Applications, testing procedures, and operational aspects of PLC equipment and systems are discussed. 

This text covers the most common programmable logic controller functions, providing practical examples based on the widely used Allen-Bradley Small Logic Controller (SLC 500) series of PLCs.

The wiring and programming of a PLC are covered thoroughly, using numerous examples. A supplemental laboratory manual provides a wealth of hands-on activities that will help students practice and hone their PLC programming skills.

It also includes a CD-ROM containing LogixPro simulation software with a textbook. LogixPro is the ideal tool to facilitate student learning of the fundamentals of RSLogix ladder logic programming. See more Info

Hope you will like these books and if you have any other good suggestions, please comment below.

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