Woodward 2301A Load Sharing Speed Control 9907-018

Description

The user program of PLC is designed by designers based on the process control requirements of the control system, using the programming language of PLC to develop specifications, and according to the actual functions needed. As long as users can master a certain standard programming language, they can use PLC to achieve various automation control functions in the control system.

According to the Industrial Control Programming Language Standard (IEC1131-3) formulated by the International Electrotechnical Commission, PLC has five standardized programming languages: Sequential Function Diagram (SFC), Ladder Diagram (LD), Functional Module Diagram (FBD), and Statement Table (IL) and Structured Text (ST)
The two most commonly used programming languages for PLC are ladder diagrams and mnemonic language tables. Here are five standardized programming languages:

1. Ladder Diagram Language (LD)
Ladder diagram language is the most commonly used programming language in PLC programming. It is a programming language similar to relay circuits. Due to the familiarity of electrical designers with relay control, ladder diagram programming language has been widely welcomed and applied.

The characteristics of ladder diagram programming language are: corresponding to the electrical operation schematic diagram, having intuitiveness and correspondence; Consistent with the original relay control, electrical designers are easy 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.

2. Instruction List Language (IL)
Instruction list programming language is a mnemonic programming language similar to assembly language, which is composed of opcodes and operands, just like assembly language. In the absence of a computer, it is suitable to use a PLC handheld programmer to program user programs. At the same time, the instruction table programming language corresponds to the ladder diagram programming language diagram one by one, and can be converted to each other under PLC programming software. Figure 3 is the instruction table corresponding to the PLC ladder diagram in Figure 2.

The characteristic of instruction table programming language is that it uses mnemonics to represent operational functions, which is easy to remember and master; Using mnemonics on the keyboard of a handheld programmer is easy to operate and can be programmed and designed in situations without a computer; There is a one-to-one correspondence with the ladder diagram. Its characteristics are basically consistent with the ladder diagram language.

3. Functional Module Diagram Language (FBD)
Functional module diagram language is a PLC programming language similar to digital logic circuits. Using a functional module diagram to represent the functions of a module, different functional modules have different functions.

The characteristics of functional module diagram programming language: The characteristics of functional module diagram programming language are: based on functional modules, analyzing and understanding control schemes is simple and easy; Functional modules express functions in the form of graphics, which is highly intuitive and easy for designers with a foundation in digital logic circuits to master programming; For control systems with large scale and complex control logic relationships, the functional module diagram can clearly express the functional relationships, greatly reducing programming and debugging time.

4. Sequential Functional Flowchart Language (SFC)
Sequential functional flowchart language is a programming language designed to meet the requirements of sequential logic control. When programming, the process of sequential flow actions is divided into steps and conversion conditions, and the functional flow order of the control system is allocated according to the transfer conditions, step by step according to the sequence of actions. Each step represents a control function task, represented by a box. Contains ladder diagram logic within the box for completing corresponding control function tasks. This programming language makes the program structure clear, easy to read and maintain, greatly reducing the workload of programming and shortening programming and debugging time. Used in situations where the scale of the system is large and the program relationships are complex. Figure 5 is a schematic diagram of a simple functional programming language.

The characteristics of sequential function flowchart programming language are: taking functions as the main thread, allocating according to the order of functional processes, clear organization, and easy to understand user programs; Avoiding the defect of ladder diagram or other languages not being able to perform sequential actions, and also avoiding the defect of complex and difficult to understand user program structure caused by mechanical interlocking when programming sequential actions using ladder diagram language; The scanning time of user programs is also greatly reduced.

5. Structured Text Language (ST)
Structured text language is a programming language that uses structured descriptive text to describe programs. It is a programming language similar to high-level languages. In large and medium-sized PLC systems, structured text is often used to describe the relationships between various variables in the control system. Mainly used for user programming that is difficult to implement in other programming languages.
Structured text programming language uses a computer based description method to describe the various operational relationships between various variables in the system, completing the required functions or operations. The structured text programming language used by most PLC manufacturers is similar to high-level languages such as BASIC, Pascal, or C, but has been simplified in terms of expression methods and types of statements for ease of application.

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