5 types of PLC programming languages

The programmable logic controller is used in various industries to run diffee pushbuttons as well as dedicated automatic switches. The PLC can be used to control a single dc motor to a huge industrial plant automatically. A different set of instructions is provided to a PLC unit and as per the provided set of instructions, the PLC functions. The set of instructions are provided to a PLC unit with the help of programming. A specific programming language is used to program a PLC. PLC programming software comes in with each PLC unit which is used to program the PLC. Different programming software is introduced to provide a gatrent plants and units automatically with a proper sequence. A programmable logic controller is first programmed as per the desired operations and after programming, it is attached to an industrial unit. There are various shapes and sizes of the PLCs which are used in various sections of an industry or a processing plant. The most important parameter in a PLC is the programming of a PLC. If a PLC is not programmed efficiently then the PLC doesn’t perform well. The controlling nature of a PLC is varied from different models of PLC. It can include simpleway between the PLC programming. The user application is developed with the help of PLC software. The software for the programming of the PLC is a Human Machine Interface which provides different connectivity means between the programmer and the PLC unit which is being programmed. After the programming of the PLC, the PLC is subjected to RUN mode and once activated the RUN mode of the PLC continues until the operation is completed or terminated by the operator through any condition. The basics of programming for the PLC are discussed before jumping towards the programming of the PLC.
 

At the heart of a Programmable Logic Controller (PLC) lies its CPU, which operates two distinct programs:

• Operating System: The operating system manages operations, sequences, and functions of the CPU unrelated to control tasks.
• User Program: Conversely, the user program is responsible for executing control tasks, including handling output signals, managing interrupts, and addressing errors.
• All the operations, sequences, and functions of a CPU that are not linked with the control task are sorted out by the operating system.

Different functions that are required during the process of a task are sorted out by the user program. The user program handles a number of tasks like handling and specifying output signals, handling the interrupts in the commands and tackling different errors.

As technology advances, a myriad of PLC units flood the market, each with its unique characteristics and properties. Although PLCs come equipped with manufacturer-specific software, several programming languages are universally recognized across the industry. Here are five common and well-known PLC programming languages:

Sequential Function Charts (SFC):

SFC employs a graphical-oriented approach, enabling programmers to code operations in chronological order. Its intuitive graphical representation simplifies comprehension, making it an ideal choice for beginners in PLC programming.

In this PLC programming language, the programmer codes in chronological order. It is a graphically oriented programming for the PLC. In this programming language, the specific code is the sequence of the different operations that will be carried out as per the code. The sequential function chart is an easy language as the graphical representation is easy to understand as compared to other programming languages.

Ladder Diagram (LD):

As the official programming language for PLCs globally, LD boasts a graphical format that facilitates ease of programming. Despite its popularity, LD may suffer from poor data structure organization, which could impact programming efficiency.

The diagram is the official programming language for the PLC as it is officially recognized as a programming language for PLC all over the world. This is also an easy programming language as it is also a graphical form of programming. In this programing language, different symbols are connected to form code and perform different actions as per the desire of the programmer. The only drawback associated with the ladder diagram programming is the poor data structure as data in this programming is not well organized.

Function Block Diagram (FBD):

FBD introduces a block-based programming approach, allowing input data to flow to outputs through nested blocks. Designed to address the limitations of previous languages, FBD offers enhanced organization of keywords, identifiers, and variables.

In this programming, the input data is sent to output via blocks of nested data. This programing language was created to overcome the limitations of the previous programming languages especially the limitations of ladder diagram programming. The main parameters in FBD programming are the keywords, identifiers, variables, and data types that need to be used efficiently. The system under a process of programming can be viewed in FBD for cross-checking whereas other programming lacks this functionality during programming. The various elements under process can be viewed during programming in this programming language for PLC.

Structured Text (ST):

ST represents PLC programming in a textual format, akin to Pascal programming. While it offers powerful capabilities, ST's structured nature may pose challenges for some users in terms of understanding and readability.

As the name suggests, the structured text is the programing language for PLC which is based on only text form. This programming is a bit difficult to understand as it is a structured text which can be difficult for a reader to understand. Different terms like Pascal programming are used in ST such as If-then-Else.

Instruction List (IL):

IL extracts instructions directly from ladder diagrams, transmitting them to PLCs via programming terminals. Unlike graphical languages, IL relies on text-based instructions, resembling assembly language in its structure. By mastering these PLC programming languages, industrial automation professionals can streamline processes, improve efficiency, and ensure optimal performance across various industrial applications.

In this programming language, the instructions are extracted from the ladder diagrams. The instructions extracted are then sent to PLC via programming terminals. It is not a graphical language instead it is a series of text. It is the same as assembly language.
 

Free ebook - Introduction to Programmable Logic Controllers