PPT: Block Diagrams & Signal Flow Graphs | Control Systems - Electrical Engineering (EE) PDF Download

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Block Diagrams
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Block Diagrams
Block Diagram in 
Control Systems
Any system can be described by a set of differential equations, or it can 
be represented by the schematic diagram that contains all the 
components and their connections. However, these methods do not 
work for complicated systems. The Block diagram representation is a 
combination of these two methods. A block diagram is a representation 
of a system using blocks. For representing any system using block 
diagram, it is necessary to find the transfer function of the system 
which is the ratio of Laplace of output to Laplace of input.
Where R(s) = Input C(s) = output G(s) = transfer function Then, the 
system can be represented as C(s) = R(s).G(s)
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Block Diagrams
Block Diagram in 
Control Systems
Any system can be described by a set of differential equations, or it can 
be represented by the schematic diagram that contains all the 
components and their connections. However, these methods do not 
work for complicated systems. The Block diagram representation is a 
combination of these two methods. A block diagram is a representation 
of a system using blocks. For representing any system using block 
diagram, it is necessary to find the transfer function of the system 
which is the ratio of Laplace of output to Laplace of input.
Where R(s) = Input C(s) = output G(s) = transfer function Then, the 
system can be represented as C(s) = R(s).G(s)
Summing Point and Take-off Point
Summing Point
When we want to apply a different input signal to the same 
block then the resultant input signal is the summation of 
all the inputs. The summation of an input signal is 
represented by a crossed circle called summing point 
which is shown in the figure below.
Take off Point
When there is more than one block, and we want to apply 
the same input to all the blocks, we use a take-off point. By 
the use of a take-off point, the same input propagates to 
all the blocks without affecting its value. Representation of 
same input to more than one block is shown in the below 
diagram.
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Block Diagrams
Block Diagram in 
Control Systems
Any system can be described by a set of differential equations, or it can 
be represented by the schematic diagram that contains all the 
components and their connections. However, these methods do not 
work for complicated systems. The Block diagram representation is a 
combination of these two methods. A block diagram is a representation 
of a system using blocks. For representing any system using block 
diagram, it is necessary to find the transfer function of the system 
which is the ratio of Laplace of output to Laplace of input.
Where R(s) = Input C(s) = output G(s) = transfer function Then, the 
system can be represented as C(s) = R(s).G(s)
Summing Point and Take-off Point
Summing Point
When we want to apply a different input signal to the same 
block then the resultant input signal is the summation of 
all the inputs. The summation of an input signal is 
represented by a crossed circle called summing point 
which is shown in the figure below.
Take off Point
When there is more than one block, and we want to apply 
the same input to all the blocks, we use a take-off point. By 
the use of a take-off point, the same input propagates to 
all the blocks without affecting its value. Representation of 
same input to more than one block is shown in the below 
diagram.
How to draw the block Diagram
Consider a simple R-L 
circuit
Start with the circuit diagram to understand 
the components
Apply KVL
Write the equations based on Kirchhoff's 
Voltage Law
Take Laplace transform
Convert the differential equations to 
algebraic equations
Derive transfer functions
Find the relationships between input and 
output variables
Apply KVL
Now taking laplace transform of Eq.1 and Eq.2 with initial condition zero
From eq. 3 and eq. 4
From fig: Now taking laplace transform of Eq.5, and Eq.6
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Block Diagrams
Block Diagram in 
Control Systems
Any system can be described by a set of differential equations, or it can 
be represented by the schematic diagram that contains all the 
components and their connections. However, these methods do not 
work for complicated systems. The Block diagram representation is a 
combination of these two methods. A block diagram is a representation 
of a system using blocks. For representing any system using block 
diagram, it is necessary to find the transfer function of the system 
which is the ratio of Laplace of output to Laplace of input.
Where R(s) = Input C(s) = output G(s) = transfer function Then, the 
system can be represented as C(s) = R(s).G(s)
Summing Point and Take-off Point
Summing Point
When we want to apply a different input signal to the same 
block then the resultant input signal is the summation of 
all the inputs. The summation of an input signal is 
represented by a crossed circle called summing point 
which is shown in the figure below.
Take off Point
When there is more than one block, and we want to apply 
the same input to all the blocks, we use a take-off point. By 
the use of a take-off point, the same input propagates to 
all the blocks without affecting its value. Representation of 
same input to more than one block is shown in the below 
diagram.
How to draw the block Diagram
Consider a simple R-L 
circuit
Start with the circuit diagram to understand 
the components
Apply KVL
Write the equations based on Kirchhoff's 
Voltage Law
Take Laplace transform
Convert the differential equations to 
algebraic equations
Derive transfer functions
Find the relationships between input and 
output variables
Apply KVL
Now taking laplace transform of Eq.1 and Eq.2 with initial condition zero
From eq. 3 and eq. 4
From fig: Now taking laplace transform of Eq.5, and Eq.6
Building the Block Diagram Step by Step
Add a summing point
For the right-hand side of eq.5, we will use a summing point.
Connect to first block
The output of summing point is given to the block, and the output of the block is I(s)
Connect to second block
The output I(s) is given to another block containing element SL and the output of this block is V0.
Complete the diagram
By combining the above steps, we get the required block diagram