You must have written this simple logic in a ladder language. Remember to not get trapped in a repetitive or infinite loop which will not break the logic and can instead confuse the programmer in writing the logic. You have to properly define the conditions and arrange the blocks and flow sequence accordingly to perform the function. SFC’s are useful in breaking a very complex flow chart sequence in a simpler way to execute the logic. In the box, you can define the action and in the black line, you can define the variable condition to be written. The below image is an actual example of the language written in PLC software. You can write a variable or even call a section in a step. A transition condition can be defined as an interlock for executing a step or action. This means that the logic will be executed as per the flow sequence lines written. If the stop button is pressed, the motor will be turned off as per the third transition condition and the second step. Now, if the start button is pressed, the motor will be turned on as per the second transition condition and third step. On PLC start-up, after a delay of 2 seconds, the motor will be turned off by default in the second step as written. The third transition condition is written for checking stop pushbutton press. The third step is written to set the motor variable. The second transition condition is written for checking the start pushbutton press. The second step is written to reset the motor variable. The first transition condition is set to true. This means that the start and stop action will be executed after an initial delay of 2 seconds of PLC start-up. This step executes on PLC cold start or warm start. In the first box, a start-up condition of 2 seconds timer is written for starting this action. The horizontal grey line in between indicates the transition condition. The brown line indicates the flow of the sequence. The black box represents action to be written inside the step. Refer to the below image showing SFC language. Sequential Flow Chart ProgrammingĬonsider a simple example where you turn on or off a motor by pressing the start and stop buttons. Instead of writing the whole logic in a ladder diagram or even if you use functional block diagrams, the repetition rates and the overall viewing of the process can be made simpler by using SFC language. This language is a very useful tool in a condition where the process is very large and the functions are performed in steps. SFC Language in PLCĪ Sequential Flow Chart is a language used in PLC programming which is a graphical representation of the flowcharts or steps, which is similar to flowchart algorithms used in computer languages. The five types of languages used in PLC programming are as follows. SFC Programming Example Types of Languages in PLC.
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