Transcript TKim

RESISTIVE, CAPACITOR,
INDUCTIVE, PIEZOELECTRIC SENSOR
2006200401
Tae-eui, Kim
Resistive 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 Resistive
R
A F
1
R
F
R
F
Thermister
ceramic
R
NTC(Negative Temperature Coefficient) Thermister
cf) PTC(Positive Temperature Coefficient)
(A) Voltage Divider
Rs
Vo 
E
R  Rs
R
E
Rs
Vo F T
Rs
(B) Inverting Amplifier
E
R
R
Vo   E
Rs
Rs
(C) Bridge Circuit
Rp
(D) Linearization
R
R
Rs
Rs RP
R
Rs  RP
Linear region
Capacitive Sensor
A
x
R
A
C   o R
x
Most capacitive sensors are based on changes in x
Inductive Sensor
① Self Inductance
② Mutual Inductance
③ Differential Inductance
Inductive Sensor
① Self Inductance
F
x
S
Vo
Inductive Sensor
② Mutual Inductance
Don’t know where it is
Vs
Vs
Vo
Vo
Inductive Sensor
③ Differential Inductance
LVDT(Linear variable Differential Transformer)
a
c
D

d
x0
Vs
f

b
D
Primary coil
e
Vo  Vcf  Vcd Vef
 Vcd  V fe
Inductive Sensor
(a) When core is at
x0
Vcd
Vo  0
V fe
; cancelled out
Inductive Sensor
(b) When core is at
x  
Vcd
Vo
V fe
Inductive Sensor
(c) When core is at
x  
V fe
Vo
Vcd
Adventage of LVDT
; You have wide of range of measuring
Problem 13
F
x(t )
x  20mm
20mm
t
40mm
20mm
Vs (t )  sin(2 1000t ) [V ]
f  1kHz
t  1ms
x  20mm
Problem 13
<Method I> Rectifier + LPF
V (t )
Vo (t )
t
LPF
Problem 13
<Method I> Rectifier + LPF
Problem 13
<Method II> phase – sensitive demodulation
V (t )
Vo (t )
t
sin(2 1000t )
Problem 13
<Method II> phase – sensitive demodulation
Problem 14
Vo (t )  x(t )sin(2 1000t   )
Vm (t )  x(t )  sin(2 1000t   )  sin(2 1000t )
  0
Problem 14
  10
Problem 14
  45
Problem 14
  45
Piezoeletric Sensor
q  kx
x
dq (t )
dx(t )
i (t ) 
k
dt
dt
dx
0
if
dt
then i  0
Piezoelectric sensor has no dc response
You cannot measure static, but dynamic
 Microphone , pulse
Piezoeletric Sensor
i(t )  Vs (t )
x(t )
i (t )
R
Vs (t )  Ri(t )
i (t )  k
dx(t )
dt
Vo (t )
Piezoeletric Sensor
② Charge Amplifier
R
C
0V
i (t )
i0
0V
1
jC
Vo   I
1
R
jC
R
Vo (t )
 I
R
j R
 k
X
1  j RC
1  j RC
Piezoeletric Sensor
dx(t )
i(t )  k
d (t )
 FFT
H
k
1
C
I  kj X
Vo
j R
H  
X
1  j RC
fc 
1
2 RC
f
If you plan to use the piezoelectric sensor for measuring pulse,
the lowest frequency of pulse signal is assumed to be 0.1Hz