The system can be represented in two forms:
•Block diagram representation
• Signal flow graph
Block diagram
A pictorial representation of the functions performed by each component and of the flow of signals
Basic elements of a block diagram
•Blocks
• Transfer functions of elements inside the blocks
• Summing points
• Take off points
• Arrow
Block diagram
A control system may consist of a number of components. A block diagram of a system is a pictorial representation of the functions performed by each component and of the flow of signals. The elements of a block diagram are block, branch point and summing point.
Block
In a block diagram all system variables are linked to each other through functional blocks. The functional block or simply block is a symbol for the mathematical operation on the input signal to the block that produces the output.
Summing point
Although blocks are used to identify many types of mathematical operations, operations of addition and subtraction are represented by a circle, called a summing point. As shown in Figure a summing point may have one or several inputs. Each input has its own appropriate plus or minus sign.
A summing point has only one output and is equal to the algebraic sum of the inputs.
A takeoff point is used to allow a signal to be used by more than one block or summing point. The transfer function is given inside the block
• The input in this case is E(s)
• The output in this case is C(s)
• C(s) = G(s) E(s)
• Functional block – each element of the practical system represented by block with its
• Branches – lines showing the connection between the blocks
• Arrow – associated with each branch to indicate the direction of flow of signal
• Closed loop system
• Summing point – comparing the different signals
• Take off point – point from which signal is taken for feed back
