The core concept of PLC ladder programming is the ladder diagram. A ladder diagram is a graphic consisting of horizontal and vertical lines that are typically used to represent the logical relationships of a circuit. In PLC ladder programming, ladder diagrams are used to represent the logical relationships of a program.
The main elements of PLC ladder programming include inputs, outputs and logic elements. Among them, input and output refer to the interface between the PLC system and the physical world, such as sensors and actuators; logic elements are used to describe the logical relationship between inputs and outputs. logic elements of PLC ladder programming include controllers, counters, timers, flip-flops, comparators, logic operators, etc. They can be used in combination to achieve complex control functions.
The following are some common techniques of PLC ladder programming:
1. Understand the control principle: Before writing ladder diagram, it is better to master the control principle, including PLC input/output, and how to achieve the control target.
2. Use structured programming style: When writing ladder diagrams, you should use structured programming techniques, such as using comments to explain logical relationships, using labels and symbols to describe inputs and outputs and trigger conditions, etc.
3. Use networks in groups: Networks should be grouped by function, and each group can contain a set of related logical processes. For example, one group could handle all the start/stop logic, while another group could handle all the alarm logic.
4. Use subroutines: Subroutines are a technique for writing maintainable programs that simplify managing complex operations. By using subroutines, common blocks of code can be put together to avoid repetitive code patterns.
5. Streamline constant definitions: When developing ladder applications, do not rely excessively on constants. If variables depend on many constants, it may make the ladder code difficult to understand and maintain.
6. self-documentation: Ladder diagrams should have clear and easy to understand comments so that other users or take over the program to make subsequent changes.
7. Ensure correct program: Testing and verification are important tasks in writing PLC ladder diagrams. Make sure that the program runs correctly with different input/output situations and when the main PLC program and other programs work together.
In summary, writing PLC ladder diagrams should focus on good programming practices and structured programming techniques.
The considerations for PLC ladder programming are as follows:
1. Ensure the correctness of ladder diagram symbols and logical correctness to avoid errors and logical faults in wiring.
2. Set the initialization state correctly for input and output points to prevent unknown states at startup.
3. Pay attention to the unit and accuracy when setting the value of timer and counter.
4. In writing ladder programs, pay attention to the uniqueness and accuracy of marker names to avoid renaming or misspelling.
5. Ensure that each program is complete and reliable. Step-by-step tests can be performed to find errors.
6. When using special function modules or library functions, read their description documents carefully to understand their operation and restrictions.
7. Insist on writing PLC programs according to specifications, such as: avoiding the use of jumpers, using equivalence links, checking loops, etc.
8. in the use of conditional jumps and other complex logic functions, should ensure that the code is simple and easy to read.
9. In the process of program design and implementation, the history of program modification should be recorded in time to facilitate future tracking or retrospective use.
10. Before PLC programming, adequate analysis of equipment and production process should be conducted before the programming program is developed to ensure programming efficiency and goal achievement.