 Hello everyone, welcome to this session on PLC programming using sequential function charts. So at the end of the session you will be able to examine the basics of sequential function charts, their structures. Also you will be able to write small s of c structures for some basic logic functions. So we know that there are five program methods which are supported by IAC standard. So let us today learn a sequential function chart method which is a graphical method in which systems operations are described by a number of separate sequentially connected states or steps represented by rectangular boxes. So what is a sequential function chart? So it is a graphical language in which complex programs are broken into smaller manageable units called as states and the control flow between them or these states is described. So sequential function charts are basically suitable for processes in which their behavior changes step by step. For example washing machine, chemical plants, etc. So here a basic structure of sequential function chart is shown with some square boxes then connection between them with some branches also. So in SFC operation is described by a number of separate sequentially connected states or steps and these are normally represented by rectangular boxes. So here you will see that it is a start step or step then you have again another step having its own output then some transition condition in between them and at the last you have again stop. So this is a basic structure of sequential function charts. So each connecting line between the states has a horizontal bar if you observe here and these bars are called as a transition conditions. So these transition conditions has to be realized before the system can move from one state to another state. So there are some conditions which should be followed. So one condition is two steps must always be separated by a transition. So there is one more condition two transitions must always be separated by a step. What is the meaning? So you cannot connect two steps directly or you cannot connect two transition conditions directly. So when the condition to the next state are realized the next state or step in the program occurs. The outputs or actions at any state are represented by horizontally linking boxes and occur when the state has been realized. So here one example is shown with the reference to a ladder diagram. So in step 0 the function sequential function chart enters into step 0 if input 1 occurs. So when step 0 is realized then and then only output 1 will occur. Again to go to step 1 input 2 should be realized and after step 1 is realized output 2 occurs. So this is the function sequential function chart for this given ladder diagram in which one switch IN1 is directly connected to output load whereas this normally open switch is dependent depend on output 1 and with one more switch into in series again connected to output 2. Now let us understand some of the basics of this SFC structures. So in sequential function chart you will have a branching facility. So there are two types of branching facilities selective and parallel. So let us understand what is selective branching. So selective branching allows for different states to be realized depending on the transfer condition that occurs. So here you will see that when output 0 occurs your state can be state 1 if input 1 realized or it can be state 2 if input 2 is realized or it can be state 3 if input 3 is realized. So state 1 occurs if the transfer condition IN occurs but if input 2 then state 2 or if input 3 then state 3. So here you have three choices after state 0. So this is selective branching. In parallel branching normally parallel branching is represented by a pair of horizontal lines allows two or more different state to be realized and proceed simultaneously. So here if output 0 occurs and if input 1 is realized all the state 1, 2 and 3 simultaneously realized. So this is nothing but parallel branching example and its equivalent ladder diagram is something. So these type of branching are now being used for multi output processes. Then we have convergence. So here one example is shown. So if input 4 occurs the sequence goes from state 2 to state 4 or from state 3 to state 4 if input 5 occurs. This is an example of convergence. Then there is one more conversion which is simultaneous conversion in which the sequence can go simultaneously from both state 2 and state 3 to state 4 if input 4 occurs. So these are few branching and convergence examples which are supported in sequential flow charts. Now there are some outputs or actions you need to specify in sequential function charts. So what are the actions? So actions are represented by rectangular boxes attached to the state. Also these actions behavior can be given by using a ladder diagram or a functional block diagram or any instruction list or a structural steps. So let us solve some examples. So let us draw a sequential function chart structure for this given ladder diagram in which three switches and two outputs are shown. So output 1 occurs if input x1 is realized whereas output 2 occurs if input 2 and input 3 realizes. So solution to this problem looks like this. Sequential function chart contains two states. So the output of first state is y1 whereas output of second state is y2. And the transition conditions are denoted with x1 and second transition condition is denoted by x2 and x3. So y1 will occur if x1 realizes state 1 and y2 will occur if state 2 is realized by x2 and x3 transition condition. So let us solve the second example. So let us draw a sequential function chart diagram for the following operation in which a start switch starts the operation. So after which a tank is filled by opening a wall 1 until a level switch 1 is triggered and the tank is drained by opening drain wall 2 until level switch 2 is triggered. And this sequence is repeated. So here if you observe we have three transition conditions one is for start switch another is for level switch 1 and third one is for level switch 2. So these are the transition conditions which you need to use in your sequential function chart. So if you draw the sequential function chart for this particular example it will look like this. So the start switch realizes the filled tank state and your output for this state is open wall 1 which starts filling the tank. So when the tank is totally filled it will trigger this level switch 1 and sequential function chart enters in drain tank state. So after entering in this state your wall 2 will be open and it will empty your tank. So empting will trigger this level to switch and at the end after empting the tank 2 the process will repeat. So these are few examples in which we learn how to draw sequential function charts for basic operations. These are the few references for further reading. Thank you.