The graphic method is to design PLC program by drawing. The common ones are ladder diagram method, logic flow chart method, time sequence flow chart method and step sequence control method.
a Ladder diagram method: Ladder diagram method uses the ladder diagram language to compile PLC programs. This is a programming method that mimics a relay control system. Its graphics and even component names are very similar to the relay control circuit. This method can easily transplant the original relay control circuit into the PLC ladder language. This is the most convenient programming method for those familiar with relay control.
b Logic flow chart method: The logic flow chart method uses a logic block diagram to represent the execution process of a PLC program and reflects the relationship between input and output. The logic flow chart method is a process flow of the system, which is represented by a logic block diagram to form a logic flow chart of the system. The logic of the PLC control program prepared by this method is clear, the causality of the input and output, and the interlocking conditions are clear. The logic flow chart will make the whole program clear, easy to analyze the control program, easy to find the fault point, and easy to debug and repair the program. Sometimes for a complex program, it may be difficult to use a statement list and ladder diagram programming directly. You can first draw a logic flow chart, and then use a statement list and ladder diagram to write a PLC application for each part of the logic flow chart.
c Timing flow chart method: The timing flow chart method first draws the timing chart of the control system (that is, the control timing chart of which control should be performed at a certain time), and then draws the block diagram of the corresponding control task according to the timing relationship. Finally, write the block diagram as a PLC program. The timing flow chart method is very suitable for programming methods of time-based control systems.
d Stepwise sequence control method: Stepwise sequence control method is to design complex control programs with the cooperation of sequence control instructions. Generally, more complicated programs can be divided into several simple function blocks. One block can be regarded as one step in the entire control process. From the whole perspective, the control process of a complex system is composed of such steps. The task of system control can actually be considered to complete the control of each step at different times or in different processes. For this reason, many PLC manufacturers have added step sequence control instructions to their PLCs. After drawing the state flowchart of each step, you can use the step sequence control instructions to conveniently write the control program.

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