Top 5 Most Popular Types of PLC Programming Languages

Top 5 Most Popular Types of PLC Programming Languages

Programming 20.10.2023 1 Comments Add to Reading List

A complete guide to the five most popular PLC programming languages: ladder logic, structured text, function block diagrams, sequential flowcharts, and instruction lists.

PLC Programming Language Terms

**The 5 most popular types of PLC programming languages of 2020 are:**

Structured Text (ST)
Sequential Function Charts (SFC)
Ladder Logic Diagram (LD)
Function Block Diagram (FBD)
Instruction List (IL)

International Electro-Technical Commission (IEC) 61131-3 plans 5 different

PLC programming languages:

ladder logic
structured text
function block diagrams
sequential function charts
instruction lists

ladder logic, structured text, function block diagrams, sequential function charts, and instruction lists. Each of these languages has advantages, weaknesses, and best use cases. As a competent PLC programmer, being aware of these options is essential to solving existing code, using the right tool for the job, and having a different perspective on how to solve problems. Additionally, depending on the PLC platform of choice, certain languages may come at a premium or not be available at all. For example, only a full license of RSLogix 5000 will have access to languages beyond Ladder Logic. Let’s take a more in-depth look at each one of these languages, go over their applications, general structure, and use cases.

Contents

PLC Programming Language Terms. 1

PLC programming languages: 1

1:- Ladder Logic PLC Programming. 4

Advantages of Ladder Logic PLC Programming. 5

Drawbacks of Ladder Logic. 5

2:- Structured Text Plc Programming. 6

Advantages of Structured Text PLC Programming. 7

Disadvantages of Structured Text 8

3:- Function Block Diagrams PLC Programming Language. 8

Advantages of Function Block Diagrams PLC Programming. 9

Disadvantages of Structured Text 10

4:- Sequential Function Charts PLC Programming Language. 10

Advantages of Sequential Function Charts PLC Programming. 12

Disadvantages of Sequential Function Charts. 12

5:- Instruction Lists PLC Programming Language. 13

Advantages of Instruction Lists PLC Programming. 13

Disadvantages of Instruction Lists. 14

Assumption. 14

10 Latest PLC Technology Trends

Top 5 Types of Programming Languages

This question is debated among PLC programmers all over the world. The consensus is that the most commonly used language for PLC programming is ladder logic. This is due to the fact that it is extremely flexible, easy to learn, and very well understood by electricians who have worked with schematics that model the same architecture.

However, over the past decade, a younger workforce has entered manufacturing. These engineers and technicians are mainly taught modern languages like Java, Python, and JavaScript. These languages are more similar to Structured Text [ST] and thus promote its use.

It is also important to consider the industry in question. A chemical process is commonly designed using a Piping and Instrumentation Diagram (P&ID). These typical schematics are easily simulated through the use of function block diagrams [FBD].

PLC Programming Languages - An example of a chemical process that would be easier to implement in Function Block Diagrams (FBD) PLC programming

1:- Ladder Logic PLC Programming

Before programmable logic controllers became popular, relay-based controls were the norm on most manufacturing sites. Relays placed loads based on simple logic that was implemented through the physical wiring of the devices. The wiring of these devices was described in electrical drawings that assumed a ladder-like arrangement. As the most basic PLCs were introduced into the field, ladder logic PLC programming was designed to mimic the layout of relay-based circuits. In other words, ladder logic was one of the first PLC programming languages that is still used today because of its simplicity.

PLC Programming Languages - PLC Schematics Leading to Ladder Logic PLC Programming

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Since its inception, ladder logic has evolved significantly. However, the basic principles of operation remain the same. Ladder logic PLC programming evaluates each section of the ladder in sequential order and evaluates the conditional instructions, and if the result evaluates to "TRUE", the output instructions are executed.

PLC Coding Languages | Ladder Logic PLC Programming Example in RSLogix 5000

Advantages of Ladder Logic PLC Programming

Simple to Implement and Troubleshoot: Ladder Logic is a visual language that provides confirmations of status for most instructions. In other words, it’s easy for someone with little knowledge of a specific process to walk through the program and understand the logic.
Modular Design: Ladder Logic can be easily modified through the addition or subtraction of logic. Each rung is a separate condition and can be removed or added as needed.
Resilience and Consistency: Ladder Logic allows the user to implement many functions. However, the language is heavily standardized and doesn’t give full flexibility, thus keeping the code consistent between different implementations.

Drawbacks of Ladder Logic

Steep Learning Curve: Ladder Logic is a simple language, so far not very natural to those who come with upbringings in C, C++, Java, or Python. That being said, it may be easier to grasp for electrical engineers and those with basic knowledge of assembly programming.
Slow Deployment: Because of the visual nature of ladder logic, it takes longer a programmer to make the logic they’ve future. There’s a need to drag and drop elements(Components) that slow down the development process versus other modern programming languages.
Unintuitive for Composite Applications: Ladder Logic sheens when it comes to sequential Boolean tasks. However, when it comes to modern control theory that involves PIDs, flow control, analog sensors, and feedback loops, it’s not always easy to implement and decipher.

Ladder Logic is the most used PLC programming language around the world. It’s easy to work with and maintain for those who don’t have constant exposure to PLC programming. We recommend that you begin your PLC programming journey by learning ladder logic first.

2:- Structured Text Plc Programming

Structured Text is a PLC programming language closely related to C or Assembly. The user enters lines of code that execute sequentially, evaluate specific functions, perform Boolean checks, and trigger the appropriate PLC output. Structured Text provides a simple transition to PLCs for those with a background in a traditional programming language such as C, C++, Java, or Python. Furthermore, it can be easily manipulated in text processors, thus quickly implemented without the

need for hardware

Structured Text PLC Programming:

Example in Studio 5000 CompactLogix PLC

Advantages of Structured Text PLC Programming

Intuitive for other programming languages: As mentioned above, Structured Text is easy to learn for those looking to transition from a software engineering background. It includes the same structures, programming paradigms, and functions that one would expect to see in C or Java.
High complexity: Structured text allows more flexibility than other languages and thus makes it easier for those who master the language to implement advanced functionality.
Transfer: Transfer Structured text is standardized in most PLC systems, making it easy to migrate between platforms. You will see significant differences in other languages between platforms, yet structured text can be implemented across hardware and software platforms.

Disadvantages of Structured Text

Difficult to troubleshoot: When compared to ladder logic programming, structured text is much more complex from a troubleshooting perspective. There are no visual queues, fewer visual aids, and generally not much code per line. People who are not comfortable with this language will have a hard time figuring out the process flow.
Error-prone: Structured text provides more flexibility to the user. However, this flexibility comes at the cost of standardization. Users should use software engineering best practices to create safe fallbacks and trap any potential software failures.

We generally recommend that you learn Structured Text only after you've mastered Ladder Logic unless you have a background in another programming language. This is not often seen in production environments due to the aforementioned drawbacks. However, it is a great way to manipulate data, and implement FOR loops and other structures that require additional steps in Ladder Logic.

3:- Function Block Diagrams PLC Programming Language

FBD is a function block diagram, a programming language designed with chemical processes in mind. It allows the user to create a visual representation and flow of processes with proper transitions between instructions. The visual editor is user-friendly, and intuitive, and creates a natural way to implement specific flows.

The most common application we have used for function block diagrams in our PLC programs is setting up PID controllers. The visual aspect of FBD makes PID easier to implement, visualize, tune, and troubleshoot in the field.

Function Block Diagram PLC Programming:

Analog Signal Scaling Example in RSLogix 5000

Advantages of Function Block Diagrams PLC Programming

Flexible visual editor: The function block diagram programming editor is very user-friendly and provides an easy way to create any layout.

Ideal for complex programming: structures In ladder logic, the user has to use more than one ring for what is possible on one FBD page. Instructions can be brought directly into complex PLC instructions that implement PID loops, motion control, and instructions (AOIs).

User-friendly: FBD's visual editor comes naturally to most users. The sequence of actions can be recreated using a drag-and-drop mechanism that takes the guesswork out of it.

Disadvantages of Structured Text

Difficult to standardize: Because of the flexibility in layout, programs written in FBD are difficult to standardize. Every PLC programmer will have a method that differs from others. Laggards will find it difficult to understand the flow of information.

Disturbing at scale: FBD shines when it comes to small implementations of specific areas of a process. However, as the program gets more complex, it's easy to get lost in all the sheets.

Function block diagrams are important in analog scaling, PID loops, and motion control. As you learn about these topics, you should begin to expose yourself to this type of PLC programming. Before that, we would recommend mastering ladder logic.

4:- Sequential Function Charts PLC Programming Language

As the name suggests, sequential function charts, or SFCs, shine when it comes to subsequent processes. For those unfamiliar with the concept, an example would be the chemical transformation of raw materials into finished products. Let's take a simple brewing process as an example.

Picture a large brewing facility with multiple tanks, valves, pressure sensors, heating elements, and a packaging section. When an operator starts manufacturing a new batch, the process goes through the following steps. Note that these steps are simple.

Step 1:-

The system is verified to be ready. Are all the right ingredients available? Are the tanks empty? Are the valves in the correct position? If the answer is correct for all the checks, proceed. If not, abort.

Step 2:-

Start filling the tank with various ingredients (water, sugar, salt, yeast, etc.). Verify the state and proceed after the tank is full.

Step 3:-

Start the brewing process. Raise and maintain the temperature for a specified period of time. Monitor tank pressure and react accordingly. Add ingredients if necessary. After the pick is complete, move to the next step.

Step 4:-

Begin the transfer to the holding tank. Our batch is ready. Verify that all appropriate valves are set in the correct position, and that the holding tank is empty, and begin the transfer process.

Step 5:-

Transfer the batch to the bottling facility.

As you can see from the example above, the process steps are performed in a sequence and the starting conditions and flow are defined as the process would run in the production facility. In ladder logic, this process can be implemented by the SQI/SQO instruction.

However, a better method would be to use SFC.

Sequential Function Charts PLC Programming:

Sequential Process Example in RSLogix 5000

Advantages of Sequential Function Charts PLC Programming

Simulating Process Flows of Most Chemical Processes: Batching is a common chemical process method that takes a fixed number of raw ingredients and converts them into a final product. SFCs shine in these applications.
Combined with ST: Most SFC editors allow the use of structured text in certain cases to create advanced logic flows.

Disadvantages of Sequential Function Charts

Unsuitable in Most Applications: It’s challenging to apply sequential function charts to a process that isn’t sequential. In other words, it has a limited number of use cases.‍
Similar Flows are Difficult to Implement and Troubleshoot: You may implement an unlimited amount of process flows through SFCs. However, as the process paths split into multiple flows, it becomes difficult to implement separate flow paths that would result in a robust sequence.

Sequential Function Charts are extremely useful in specific cases. However, trying to fit this type of programming language into a case that isn't sequential quickly leads to frustration. As you work in a manufacturing environment, we recommend that you become familiar with the process, understand the flow of the product and seek to build a model on paper before diving into SFC programming.

5:- Instruction Lists PLC Programming Language

Instruction lists are often confused with structured text because of their similar editors. These two PLC programming languages are commonly seen on different platforms because their flow is similar. For example, Codesys-based controllers will allow users to implement logic in lists of instructions, while RSLogix 5000-based controllers only have access to structured text.

In terms of program flow, each line defines instructions as well as execution conditions and results. In many respects, instruction lists are closer to how you would implement ladder logic programs than structured text. However, any language is capable of generating the same process flow.

Advantages of Instruction Lists PLC Programming

Highly standardized: Instruction lists follow a strict structure that requires the user to explicitly create variables, define conditions, and list each instruction. There is very little difference between program implementations which leads to easy-to-understand code.
Instruction Focus: As the name would suggest, there is a high level of emphasis on instructions rather than data flow. This style of programming creates a level of clarity in how data is processed in a program.

Disadvantages of Instruction Lists

Unavailable on Most PLC Platforms: As stated above, Training Lists aren’t a general method of programming as they come unusually to most programmers. They’re closer to what one would see in assembly rather than any other programming language on the market.

Assumption

The five most popular PLC Programming Languages are Ladder Logic, Structured Text, Function Block Diagrams, Sequential Flow Charts, and Instruction Lists.

These programming methods are available on most platforms. However, some PLCs will restrict user access to certain languages unless the user pays a premium.

We recommend that every PLC programmer start with ladder logic as this method is the most common in the industry. That being said, as one encounters advanced programming methods, it is important to learn other languages that can provide an easy way to implement specific processes.

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Top 5 types of Programming Languages

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