RESISTIVE, CAPACITOR, INDUCTIVE, PIEZOELECTRIC SENSOR 2006200401 Tae-eui, Kim.
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Transcript of RESISTIVE, CAPACITOR, INDUCTIVE, PIEZOELECTRIC SENSOR 2006200401 Tae-eui, Kim.
RESISTIVE, CAPACITOR, INDUCTIVE, PIEZOELECTRIC SENSOR
2006200401 Tae-eui, Kim
Resistive SensorResistive Sensor
① Strain gage : changes in
② Force sensing resistor : changes in A
③ Thermistor : change in T
④ Potentiometer changes in L
Forcing Sensing ResistiveForcing Sensing Resistive
A F1RF
R
F
R
ThermisterThermister
ceramic R
NTC(Negative Temperature Coefficient) Thermistercf) PTC(Positive Temperature Coefficient)
(A) Voltage Divider
(B) Inverting Amplifier
so
s
RV ER R
oV F T
os
RV ER
R
sR
sR R
E
E
(C) Bridge Circuit
(D) Linearization
pR
sR
R
Linear region
R
sR
s P
s P
R RRR R
Capacitive SensorCapacitive Sensor
o RACx
A
Rx
Most capacitive sensors are based on changes in x
Inductive SensorInductive Sensor
① Self Inductance
② Mutual Inductance
③ Differential Inductance
Inductive SensorInductive Sensor
① Self Inductance
F
x
oVS
Inductive SensorInductive Sensor
② Mutual Inductance
Don’t know where it is
oV
sV
sV oV
Inductive SensorInductive Sensor
o cf cd efV V V V
cd feV V
③ Differential InductanceLVDT(Linear variable Differential Transformer)
sV
a
b
c
d
e
f
D
0x
D
Primary coil
Inductive SensorInductive Sensor
(a) When core is at 0x
cdV
feV
0oV ; cancelled out
Inductive SensorInductive Sensor
(b) When core is at x
cdV
feV
oV
Inductive SensorInductive Sensor
(c) When core is at x
cdV
feV
oV
Adventage of LVDT; You have wide of range of measuring
Problem 13Problem 13
( )x t
t
20mm
20mm
( ) sin(2 1000 )sV t t [ ]V1f kHz1t ms
40mm
F
20x mm
20x mm
Problem 13Problem 13
<Method I> Rectifier + LPF
( )oV t
( )V t
LPF
t
Problem 13Problem 13
<Method I> Rectifier + LPF
Problem 13Problem 13
<Method II> phase – sensitive demodulation
( )oV t
sin(2 1000 )t
( )V t
t
Problem 13Problem 13
<Method II> phase – sensitive demodulation
Problem 14Problem 14( ) ( )sin(2 1000 )oV t x t t
( ) ( ) sin(2 1000 ) sin(2 1000 )mV t x t t t
0
Problem 14Problem 1410
Problem 14Problem 1445
Problem 14Problem 1445
Piezoeletric SensorPiezoeletric Sensor
x
q kx
( ) ( )( ) dq t dx ti t kdt dt
0dxdt
0i if then
Piezoelectric sensor has no dc responseYou cannot measure static, but dynamic
Microphone , pulse
Piezoeletric SensorPiezoeletric Sensor
( )x t ( )i t R ( ) ( )sV t Ri t
( )( ) dx ti t kdt
( )oV t
( ) ( )si t V t
Piezoeletric SensorPiezoeletric Sensor
② Charge Amplifier
0V
0V
0i
R
C
( )i t( )oV t
1
1o
Rj CV I
Rj C
1 1R j RI k Xj RC j RC
( )( )( )
dx ti t kd t
I kj X
FFT
Piezoeletric SensorPiezoeletric Sensor
1oV j RHX j RC
f
1kC
H
12cf RC
If you plan to use the piezoelectric sensor for measuring pulse, the lowest frequency of pulse signal is assumed to be 0.1Hz