 Hello everyone, welcome to this session on PLC programming using functional block diagrams. At the end of this session, you will be able to examine the structure of functional block diagram programming and the basic symbols which are used to draw the functional block diagrams. You will also able to write simple functional block diagram for again simple basic logic functions. Let us revisit this techniques which are used for PLC programming. These techniques are supported by standard IEC 61131 and part 3 of this standard mainly focuses on the programming techniques used for the PLCs. So we know that there are five programming methods used for PLC programming. First one is the ladder diagram, then functional block diagram, instruction list, sequential function charts and structural steps. So out of these five instruction list and structural text programming methods are text based whereas remaining are all graphical based methods. So we can refer this IEC standard for in detail guidelines of the programming methods for PLCs. Let us dive into the functional block diagram programming. So this is a graphical language which is used for PLC programming which shows the signal and data flows through the graphical blocks. So whenever any program instruction unit in this FVD executes, it provides one or more output values. You can also copy a functional block multiple times or use distance but with associated identifiers. So multiple copies and instance are allowed. So this is how a simple functional block looks like having multiple inputs and one or more outputs. So inputs enters from the left side whereas outputs emerges from the right side with a function always specified inside the square walks. So let us go through the four graphical objects which are used in normal functional block diagram programming. So first object is connections. So in FVD you can have horizontal connections for connecting any two blocks or two elements. Similarly we can have vertical connections with multiple horizontal connections. So these connections are mainly used to connect different blocks or elements of a functional block, functional block diagram programming. But whereas wired or kind of connections are forbidden in the FVD programming. So multiple outputs are together and applied to next element is not allowed in functional block diagram programming. So how to get around it? So outputs of a functional blocks shall not be connected together that is wired or and this is not allowed in functional block diagram whereas it is allowed in ladder diagrams. So these outputs are wired or together and applied to the next element. So how to get around this? So you can use a Boolean or block which will help you to or all the outputs and you can apply this to the next stage. Next are the elements which are used for execution control. So you can have here unconditional return with this symbol. So here this left side is always one. So this will always return back whereas this is a conditional return. So when this Boolean expression is true then and then only it returns then you can have unconditional jump. So jump to the required lab or element unconditional jump then you have conditional jump. So when this Boolean expression is true or one then and then only jump will be. So these all are defined in IEC 61131 part 3 standard. Next are the graphical objects. So graphical elements to call a function or a function block itself. Again you have here standard function blocks or you can define your own function block depending upon your requirement. So again these elements are represented by square boxes with inputs and outputs. Then fourth one we have connectors which are used to continue a network on a new line at the left hand side of a screen of paper. So here this is one network which accepts outputs from previous networks. So normal these connectors are used to connect different network blocks together which are placed in different screens or print pages. So this connection one here is an example of output connector whereas this connection on this left side is an example of an input connector. Now these are the few symbols I have shown here. The first symbol is the AND gate function block. Here A, B are the inputs and output is always ending of A and B. Then ORing function block OR gate function block where output is always ORing of A and B. So output is 1 if either of A and B or both are 1. So here greater than or equal to 1 is represented or is shown inside this block whereas for AND gate ampersand is shown inside the function block. XOR gate so this equal to 1 is shown inside the XOR function block. For NOR gate the block is almost same as OR gate with the exception on the output side the output is negated. Next negated input and negated output. So these are few symbols which you can use for writing simple functional block diagrams. Now let us go through some examples how to draw functional block diagram. So let us develop a functional block diagram for a simple Boolean function. So here function is q is equal to A plus B bar. So if you observe this expression carefully you will see that here one OR operation is listed and one inverter, inverted operation is also listed. So obviously we require one OR gate and one inverter. So how to achieve this in the function block diagram programming. So here how the function block looks like for this particular q. So A is applied as it is whereas B is applied negated to a OR function block. So here output is A plus B bar. So instead of one function block which we have used here which we have learned here negated output we have directly shown a small bubble at the input side for B. Let us go to the next real-time problem. Let us develop a functional block for this given task. A lamp is required to be switched on if a pump is running and the pressure is satisfied or if the lamp test switch is closed. So let us take some time and let us draw a functional block diagram for this particular example. So if you read this statement carefully you will see that the lamp will be on if both pump and pressures are satisfactory or if the lamp switch is closed. I have written a Boolean expression here for this lamp which shows you a Boolean operation. So just I converted this statement into a Boolean expression. So this statement reads like this when pump is running and pressure is satisfactory lamp can be turned on or if the test switch is on then also a lamp can be on otherwise lamp is off. So if you observe this expression carefully you will require here one OR gate and one AND gate. So output of this AND gate is OR together with a test switch. So let us go through how this function block diagram looks like. So here this AND block accepts a running pump signal and satisfactory pressure signal as inputs and the output of this AND block is OR together with a test switch signal. So when either of these two signals are high or both high then and then only lamp will be on otherwise lamp will be off. So this is how you can write a functional block diagram for real time applications using these simple symbols which we learn in this lecture. So for further reading you can go through these books or IEC 61131 part 3 standard. Thank you.