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.
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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.
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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.
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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)
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• 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