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HW #3
2004200456
Lim Myeong Jun
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Resistive sensor
Capacitive sensor
Inductive sensor
LVDT
Problem solution
Piezoelectric sensor
Electromagnetic spectrum
Radiation thermometer
∵ ρ : Specific resistance
1.
2.
3.
4.
Strain gage : Changes in L & ρ
Force sensing resistor : Changes in A
Thermister : Changes in temperature
Potentiometer : Changes in Length
F
R
Ceramic
R
NTC thermister
(Negative temperature coefficient)
PTC thermister
(Positive temperature coefficient)
A)
R
+
E [v ]
Rs
B)
-
Vout
Rs
Vo, Vs, F, T : Non linear
R
E [v ]
+
C ) Bridge circuit
D ) Linearization
Rs
Rp
Rp
Rs
R
Linear range
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Capacitive sensor
x

εR
A
Inductive sensor
1.Self Inductance
2.Mutual Inductance
3.Difference Inductance
Most capacitive sensor
is based on changes in x.
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LVDT(Linear Variable Differential Transformer)
a
c
x=D
x= δ
d
x=0
x=-δ
b
x=-D
Primary coil
e
f
Magnetic core
+
Vo
-
Mutual Inductance Sensor
Line is Vs and dot is Vo at
magnetic core
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When core is x=0
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When core is x=+δ
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When core is x=- δ
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Vertical displacement
Given by Vs(t) = sin(2π*1000t) [V] (f = 1000Hz, T = 1ms)
180º Phase change
Method 1: Rectifier + LPF
Full
wave
rectifier
x=D
x=0
x=-D
D=20mm, 2D=40mm
LPF
V(t)
t
Method 2: Phase-Sensitive demodulation
x(t)·Vo²(t)
Vo(t)
LPF(Low Pass Filter)
x(t) = sin(2π· 1000t)
V(t)
t
V(t)
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In phase-sensitive demodulation
Vo(t)
Vm(t)
x(t) = sin(2π· 1000t)
LPF(Low Pass Filter)
V(t)
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formula
x
q : Charge , x : Deflection
Fig. piezoelectric sensor
That means piezoelectric sensor
has no DC response.
1)
i=0
i(t)
+
IA
R
i=0
Vs(t) = R*i(t)
Vo(t)
R
2)
C
i(t), Current flow
-
0V
IA
Vo(t)
+
Change Amplifier
|H|
k/c
fc
= 1/2πRC
f
If you plan to use the
piezoelectric sensor, for
measuring pulse, the lowest
frequency of pulse, signal is
assumed to be 0.1Hz