专业英语Lesson 6 Dynamic Performance 《测控技术与仪器英语教程》

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6.2 First-order Systems
• a) step response
ideal response
output
actual response
time
Figure 6.4 The step response of a first-order system
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6.2 First-order Systems
• A first-order differential equation :
ad0
dt
b0
ci
a b
ddt0
bci
a , Kc
b
b
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6.2 First-order Systems
Lesson 6 Dynamic Performance
• Backgrounds • Text tour • Language in use
– Vocabulary – Structure – Reading/writing techniques
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6.1 Zero-order Systems
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6.4 Step-response Specification
output
105% 100% 95%
90%
tr t res
ts
t r rise time t res response time t s 5 % settling time
Time(s)
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6.3 Second-order Systems
• is a measure of the damping present in a system and is
equal to the ration of actual damping to critical damping:
Figure 6-9 Graph of % overshoot against damping ratio
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6.3 SeBiblioteka ond-order Systems
• frequency response
Figure 6-10 Frequency response of a second-order system
d d 220 t2n •d d 0tn•0K i
• In terms of the D operator
0 i
(1n 2)D2K (2/n)D1
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6.3 Second-order Systems
i
K
(1n2)D2(2/n)D1
0
Figure 6.7 Block-diagram representation of a second-order system
Figure 6-11 Step response illustrating response, rise, and settling times
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6.5 Frequency-response Specification
• A.V. devices: working over a range or band of frequency
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6.4 Step-response Specification
• Three terms are used to specify a system’s step time, rise time, and setting time : ⅰ) Response time ( t res ) ⅱ) Rise time ( t r ) ⅲ) Settling time ( t s )
• Zero-order Systems ：output is proportional to the input
no matter how the input varies
0 Ki
0 K i
i
K
0
Figure 6.2 Block-Diagram Representation of a Zero-order System
• the standard form of the transfer operator :
0 K i 1 D
D d dt
,
D2 d2 dt 2
i
K
1 D
0
Figure 6.3 Block-diagram representation of a first-order system
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Figure 6-6 Frequency response of a first-order system
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6.3 Second-order Systems
• A second-order system
ad20
d2t
bdd0tc0
ei
• a standard second-order system
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6.3 Second-order Systems
• step response
Figure 6-8 Step response of a second-order system
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6.3 Second-order Systems
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6.2 First-order Systems
• b) Frequency response
Figure 6.5 Output response to a sin-wave input
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6.2 First-order Systems
ⅰ) when 1 this system is here said to be underdamped ⅱ) when 1this is the critically damped condition ⅲ ) when 1 here the system is overdamped
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