To write a PLC program can be carried out according to the following steps:
1. Process analysis
PLC control object work and control requirements are analyzed, to clarify the following questions:
1) how to start the process? The goal is how to further implement?
2) correspond to how input and output? On the timing and what are the characteristics?
3) to record and store data? How much volume of data to be stored?
4) there is no analog, digital control? What control law and the output method to use?
5) what are the requirements for system monitoring? Measures to be taken?
Process analysis is to get a clear answer to the above question.
2. Channel allocation
PLC input numbers and control objects corresponding to the input signal, output control points and output circuits are also appropriate. If analog, analog style, also to the actual PLC, so that the actual channel allocation is assigned to PLC input points of the actual input circuit, certain points of PLC outputs number is assigned to the output circuit. Programming press the dot build logic or control relationship, connection point, “condemnation“ wiring. In this way, PLC may be properly controlled.
Channel allocation in the hardware should be taken to prevent jamming of the output signal to the input signal, and to facilitate wiring. To this end, the input and output module should be focused arrangements as well.
In the software, I/O is assigned the best according to certain rules, easy to use Word command or subroutine programming and increase efficiency.
Particular case or an actual input numbers more than the PLC input, or action than the output of the PLC output control points. Then, on entered signal can in into PLC Qian, with wiring for some logic combination, put a points, to two or multiple by series or parallel Hou of entered signal, or with a points,, respectively to two a points, with output points in its intercropping switch; output points enough, also can for corresponding combination, just such by external wiring to combination cannot too more, too more has, on lost has PLC of flexibility. Point is not enough, the PLC is to use more points as well.
3. Draw a ladder diagram
Draw a ladder diagram, it is write a PLC program. Users can select their own programming (such as experience, analysis, diagrams) programming.
PLC program to organize, especially procedures more complex, we will strive to modular, divided into modules to prepare. OMRON PLC program block relies on programmers subroutines, step into its own organization.
4. Loading and debugging a program
Good programs to be loaded after the PLC in order to debug. Loading through the hand-held programmer, graphics programmer, or a personal computer to complete. In order to use the hand-held programmer, you also need to form a ladder diagram into a statement. If you use your computer or graphics programmer programming directly in ladder form.
Offline programs can not no problems, and these problems are only in the process of debugging, can be resolved.
To debug using a programmer or computer, or through a number of signals that control the State of an object for easy viewing, the PLC‘s work as “transparent“. Meanwhile, also forced some State of the PLC, makes a point to ON or OFF, so easy to identify problems, analyze and solve problems, and the program continues to improve, to achieve the desired objective.