The programmable logic controller is used in various industries to run different 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 simple 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 gateway 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.
PLC Programming Basics:
The PLC’s CPU runs two different programs which are:
- The operating System
- The user program
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.
Programming Languages for PLC:
With the advancements in technologies, a number of PLC units are available in the market with their specific characteristics and properties. Most of the PLCs come with their specified software which is then used to program a PLC. So the programming language for a PLC changes from manufacturer to manufacturer. However, 5 common and well-known programming languages for PLC are:
Sequential Function Charts.
this PLC programming language, the programmer codes in the 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 easy language as the graphical representation is easy to understand as compared to other programming languages.
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.
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 the ladder diagram programming. The main parameters in the 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.
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 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.
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.