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2.7 Block Diagram 、 signal graph and mason rule. Block Diagram is a kind of tool showing component performance,system construction and signal direction 。. 2.7.1 Block Diagram element （ 1 ） Block :shows function relation between output and input 。.
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Block Diagram is a kind of tool showing component performance,system construction and signal direction。
Signal line：have arrow which shows signal flow direction, signal nearby.
（2）comparison point（Summing Point）
2 or many signal addition or reduction。
“+” addition ，“” reduction 。“+”can be ignored。
(3) Branch Point （output point、measuring point）
note：same position has same signal。
(1)forward path TF—assuming N(s)=0
when feedback interrupted，the ratio of output C(s) and input R(s) ,or C(s) and E(s)
(2)feedback path TF assuming N(s)=0
the ratio of chief feedback signal B(s) and output C(s) 。
(4) Closedloop Transfer Function(assuming N(s)=0)
the ratio of output C(s) to input R(s) 。
Because of：
modify
**
please remember
That is
the ratio of error E(s) to input R(s)。
substitute
To equ. Above,canceling G(s) ：
2.7.3 drawing block diag.
(1）considering load effect,write the each part's differential equ. or TF,express in block diag..
(2) according to the signal direction,use the signal line to link every block.
System block diag. is also a kind of system's math model.
drawing RC circuit block diag. .
From fig.220，using kichihoff rule：
Take Laplace transform：
fig220
（1）according to circuit rule, and write differential equ. and its Laplace transformation, also can directly draw out circuit calculating diagram ( b)(2) according to 4 listing formulas make block diagram;(3) according to signal flow direction,link the every block one by one.
Exam.29
From the fig., R2C2 iis the load of R1C1，affects R1C1output voltage load effect.
（1）series
Fig 223 series
N:series no.
conclusion：The equivalent TF is the products of all the TF.。
Fig 224 parallel
Characteristics：every component input is the same R(s)，output C(s) is the sum of all the output.
(
s
)
C(S)
C
(
s
)
C
(
s
)
R
(
s
)
R
(
s
)
±
±
＋
＋
C
(
s
)
P(s)
Q(s)
Q
(
s
)
P
(
s
)
C(S)
C
(
s
)
C
(
s
)
（5）neighboring comparison point and branch point（output）move
forwardback
forwardback
Fig 226 neighboring point move
G1
R（s）
C（s）
+
( a )
G1
+
+
–
H
Exm. Solve C(s)/R(s) in the system shown in following diag.
G2
R（s）
C（s）
+
G1
+
+

H
G1
1+
R（s）
G2
(b)
1+G1H
G1
R（s）
C（s）
G1+G2
(c)
1+G1H
exam. Solve C(s)/R(s) in the system shown in following diag.
R（s）
C（s）
G1
G2
+
+
+
+
Give TF C(s)/R(s)in fig. 228 system
This is a system of many crossing tracks .if do not transform it,it is difficult to reduce with series, parallel and feedback.method is as follows.
Fig 228
feedback
Simplify fig.29.
assure forward path TF is a constant;
assure feedback loop TF is a constant;
Note :symbol change
Homework: 217