1. Experience design method of PLC program
In the early stage of PLC development, the ladder program was designed by designing the relay circuit diagram. On the basis of some typical ladder diagrams, the ladder diagram was continuously modified and improved according to the control requirements of the controlled object. Sometimes it is necessary to repeatedly debug and modify the ladder diagram, and constantly increase the intermediate programming components and contacts, in order to get a satisfactory result. There is no universal law to follow in this method. The time used for design and the quality of the design have a lot to do with the experience of the programmer. Therefore, some people refer to this design method as the empirical design method. It can be used for ladder programming with a simpler logic relationship.
When designing a PLC program by empirical design method, it can be roughly carried out according to the following steps: analysis control requirements, selection of control principles; design of master components and detection components, determination of input and output devices; design of control components of control components; inspection and modification procedures .
2. Characteristics of the experience design method
The empirical design method works well for some simpler programs and can receive fast and simple results. However, since this method mainly relies on the experience of the designer to design, the requirements for the designer are relatively high, especially the designer is required to have certain practical experience, and various typical models commonly used in industrial control systems and industry. The link is familiar. The empirical design method has no rules to follow, and it has great exploratory and random nature. It often needs to be repeatedly modified and improved to meet the design requirements. Therefore, the design results are often not very standardized and vary from person to person.
The empirical design method is generally suitable for designing some simple ladder programs or some partial programs of complex systems (such as manual programs). If you are designing a complex system ladder diagram, the following problems exist:
1). Poor consideration, troublesome design, long design cycle
When designing ladder programs of complex systems by empirical design method, a large number of intermediate components are used to complete functions such as memory, interlocking, interlocking, etc. Since there are many factors to be considered, they are often intertwined and difficult to analyze. And it is easy to miss some problems. When modifying a partial program, it is likely to have an unexpected impact on other parts of the system. It often takes a long time and does not yield a satisfactory result.
2). Ladder diagram is poorly readable and difficult to maintain
Ladder diagrams designed with empirical design are designed according to the designer's experience and habits. Therefore, even the designer's peers, it is very difficult to analyze such a program, not to mention the maintenance personnel, which brings many difficulties to the maintenance and improvement of the PLC system.
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