Programmable controller of five kinds of standard programming languages

The PLC user program is design personnel according to the requirements of the control system of process control, through the formulation design of PLC programming language. According to the standards of industrial control programming language set by the international electrotechnical commission ( IEC1131- 3) 。 PLC controller programming language includes the following five kinds: ladder diagram language ( LD) , the instruction list language ( IL） The functional module chart, language ( FBD） , sequence function diagram language ( SFC） And structured text language ( 圣) 。 1, the ladder diagram language ( LD) Ladder diagram language is commonly used in the PLC program design of programming languages. It is similar to relay circuit of a programming language. Due to the electrical design personnel of relay control more familiar, therefore, ladder diagram programming language has been widely welcomed and application. Ladder diagram programming language is characterized by: with electrical graph corresponding to the operating principle, intuitive and correspondence; Consistent with the original relay control, electrical design personnel easy to master. Ladder diagram programming language is the difference with the original relay control and ladder diagram of the electric current can flow is not the actual meaning, the internal relay is not a real relay, applications, need with the original relay control concept. Figure 1 is a typical ac asynchronous motor start control circuit diagram directly. Figure 2 is the process of the PLC controller control ladder diagram. Figure 1 ac asynchronous motor starting circuit directly Desmond tutu and instruction of PLC ladder diagram 2 table language ( IL） Instruction table programming language is a mnemonic similar to that of the assembly language programming language, and assembly language is composed of operation code and operands. Under the condition of without a computer, suitable for PLC handheld programmer to a user program compiled. At the same time, the instruction table programming language diagram and ladder diagram programming language one to one correspondence, can transform mutually under the PLC programming software. Figure 3 and figure 2 the PLC ladder diagram corresponds to the instruction sheet. Figure 3 instructions table table programming language features are: mnemonics are used to indicate the operation function, is easy to remember, easy to master; On the keyboard of handheld programmer USES the mnemonic representation, convenience of operation, can be in the absence of the occasion of computer programming design; Have a one-to-one correspondence relationship with ladder diagram. Its basic characteristics and ladder diagram language. 3, function module diagram language ( FBD） Function module diagram language is similar to digital logic circuit of a PLC programming language. Takes the form of function module diagram to represent the module with the function of different function modules have different functions. Figure 4 is corresponding to the figure 1 functional module chart of the ac asynchronous motor direct start programming language expression. Figure 4 functional module chart function module chart of the programming language features: the characteristics of function module diagram programming language is that, for the unit with the function module analysis to understand the control scheme is simple and easy; Function module is in the form of graphic expression function, intuitive is strong, with the design of digital logic circuit base personnel easy to master programming; With large scale and control logic relations of complex control system, due to the function module chart can clearly express the function relation, make the programming and debugging time greatly reduced. 4, order function flow diagram language ( SFC） Sequence function diagram language is designed to meet the sequence logic control programming language. When programming the process of order process action can be divided into steps and transition conditions, according to the transfer of conditions on the distribution function of the control system of process sequence, step by step in accordance with the action sequence. Every step on behalf of a control function task, expressed in the box. The box contains used to complete the corresponding task of ladder diagram logic control functions. This kind of programming language to make the program structure is clear, easy to read and maintain, and greatly reduce the workload of programming, the programming and debugging time. Used in the system the size of the school, program relations more complex situations. Figure 5 is a simple function flow diagram of the programming language. Figure 5 order function flow chart of the programming language characteristics: to function as the main line, distribution in accordance with the order of the function process, clear, easy to understand user program; To avoid the defect of ladder diagram or other languages can't order, and also to prevent the action when programming in ladder diagram language to order, caused by mechanical interlock user program structure complicated, difficult to understand the defect; The user program also greatly shorten the scan time. 5, structured text language ( 圣) Structured text language is the description of the structured text is used to describe a programming language of the program. It is similar to a programming language of high-level languages. In the large and medium-sized PLC system, often structured text is used to describe the relationship between the different variables of the control system. Mainly used in other programming languages is difficult to achieve the user program compiled. Structured text programming language used to describe the description of the computer system in the operation of relationship between variables, complete the required function or operation. Most of the PLC manufacturers use structured text programming language and BASIC, PASCAL language and C language is similar to a high-level language, but for the sake of convenient application, in a statement expression method and simplified in such aspects as the kinds of statements.
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