signal flow (1)
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MEC308CONTROLS THEORY
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Lecture 9
Signal Flow Graph
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Signal Flow Graph: An alternate approach for graphical representation of control system dynamics• Is a diagram that represents a set of simultaneous linear algebraic equations
• Hence for analysis of control system , their mathematical model which are linear differential equations are first transformed into algebraic equations in complex variable(s).
•Consists of a network in which nodes are connected by directed branches.
•Each node represents a system variable.
•Each branch connected between two nodes acts as a signal multiplier.
• Signal flows in only one direction.
• The direction of signal flow is indicated by an arrow placed on the branch.
• The multiplication factor is indicated along the branch
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Terminologies related to Signal flow graph:
(i) Node : A node is a point representing a variable or signal.(ii) Transmittance : The transmittance is a real gain or complex gain
between two nodes. Such gains can be expressed in terms of the transfer function between two nodes.
(iii) Branch : A branch is a directed line segment joining two nodes. (iv) Input node or source : An input node or source is a node that has
only outgoing branches. This corresponds to an independent variable.
(v) Output node or sink : An output node or sink is a node that has only incoming branches. This corresponds to a dependent variable.
(vi) Mixed node : A mixed node is a node that has both incoming and outgoing branches.
(vii) Path : A path is a traversal of connected branches in the direction of the branch arrows.
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Terminologies related to Signal flow graph: (contd…)(vii) Loop : A loop is a closed path.
(viii) Loop gain : The loop gain is the product of the branch transmittances of a loop.
(ix) Non-touching loops : Loops are non touching if they do not posses any common nodes.
(x) Forward Path : A forward path is a path from an input node(source) to an output node (sink) that does not cross any nodes more than once.
(xi) Forward path gain : A forward path gain is the product of the branch transmittances of a forward path.
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Signal Flow Graphs of Control SystemsBlock Diagram Signal Flow Graph
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Signal Flow Graphs of Control SystemsBlock Diagram
Block Diagram
Signal Flow Graph
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Problem: Draw the signal flow graph for the following block diagram.
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Solution:
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Mason’s Gain Formula For Signal Flow Graph:
It is given by:
• Helps to determine the overall transmittance between the input and output node of a signal flow graph.
Overall gain,
n = no. of forward paths
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To Find the Transfer Function of a System represented by a Block Diagram using Mason’s Gain Formula:
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The Signal Flow Graph For The Given Block Diagram Would Be:
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Forward path-2
Forward path-1P1 =G1G2 G3
P2=G4
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