The programming language of PLC is as follows:
1. Ladder Diagram (LD)
2. Functional Block Diagram (FBD)
3. Sequential Function Chart (SFC)
4. Structured Text (ST)
5. Instruction List (IL)
Language type
The user program of PLC is designed by the designer according to the process control requirements of the control system, through the programming specifications of the PLC programming language, according to the actual needs of the functions used. As long as users can master some standard programming language, they can use PLC in the control system to realize various automatic control functions.
According to IEC 1131-3, PLC has five standard programming languages: Ladder Diagram Language (LD), Instruction Table Language (IL), Function Module Language (FBD), Sequential Function Flow Chart Language (SFC), Structural Textualization Language (ST). These five standard programming languages are very easy to learn.
ladder diagram
Ladder diagram language is the most commonly used programming language in PLC programming. It is a programming language similar to relay circuit. Because electrical designers are familiar with relay control, ladder diagram programming language has been widely welcomed and applied. The characteristics of ladder diagram programming language are that it corresponds to electrical operation schematic diagram, has intuition and correspondence, and is consistent with the original relay control, which makes it easy for electrical designers to master. The difference between the ladder diagram programming language and the original relay control is that the energy flow in the ladder diagram is not the actual current and the internal relay is not the actual relay. When applied, it needs to be treated differently from the original concept of relay control.
Instruction Table Language
Instruction Table Programming Language (ISP) is a mnemonic programming language similar to assembly language, which is composed of operation codes and operands as assembly language. In the case of no computer, it is suitable to use PLC handheld programmer to compile user program. At the same time, the instruction list programming language corresponds to the ladder diagram programming language diagram one by one, and can be converted to each other under the PLC programming software. Figure 3 is the instruction list corresponding to the ladder diagram of Figure 2 PLC. The characteristics of instruction list programming language are: using mnemonics to express operation function, easy to remember and master; using mnemonics to express on the keyboard of handheld programmer, easy to operate, and programming design without computer; and having a one-to-one correspondence with ladder diagram. Its characteristics are basically consistent with the ladder diagram language.
Function Module Diagram Language
Function module diagram language is a kind of PLC programming language similar to digital logic circuit. Function modules are represented in the form of functional module diagrams. Different functional modules have different functions. Features of Function Module Diagram Programming Language: Function Module Diagram Programming Language is characterized by: simple and easy to analyze and understand control schemes in terms of function modules; Function modules are graphical forms of expression functions, strong intuition, easy to master for designers with the basis of digital logic circuits; Large-scale control systems with complex control logic relations Because the function module diagram can clearly express the function relationship, the programming debugging time is greatly reduced.
Sequential Functional Flow Chart Language
Sequential Functional Flow Chart Language is a programming language designed to satisfy sequential logic control. In programming, the process of sequential process action is divided into steps and transformation conditions. According to the transfer conditions, the functional process sequence of the control system is allocated and the sequential action is carried out step by step. Each step represents a control function task, which is represented by a box. Ladder diagram logic is included in the box to complete the corresponding control function tasks. This programming language makes the program structure clear, easy to read and maintain, greatly reduces the workload of programming and shortens the time of programming and debugging. It is used in the occasion of large-scale calibration of the system and complicated program relationship. The characteristics of sequential function flow chart programming language are as follows: taking function as the main line, distributing according to the sequence of function flow, organizing clearly, making it easy to understand user program; avoiding the defect that ladder diagram or other languages can not act sequentially, and avoiding the defect that user program structure is complex and difficult to understand when programming sequential action with ladder diagram language, because of mechanical interlocking; Household program scanning time is also greatly shortened.
Structured Text Language
Structured text language is a programming language that describes programs with structured descriptive text. It is a programming language similar to a high-level language. In large and medium-sized PLC systems, structured text is often used to describe the relationship between variables in the control system. It is mainly used in user programming which is difficult to implement in other programming languages.
Structured text programming language uses computer description to describe all kinds of operation relations among variables in the system, completing the required functions or operations. The structured text programming language adopted by most PLC manufacturers is similar to BASIC, PASCAL or C, but for the convenience of application, it simplifies the expression methods and types of sentences. The characteristics of structured text programming language are as follows: high-level language can be used to program, which can accomplish more complex control operations; knowledge and programming skills of computer high-level language are needed, which requires higher requirements for engineers. Intuitionism and operability are poor.
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