Medical Instrumentation
description
Transcript of Medical Instrumentation
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HW #32004200456
Lim Myeong Jun
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Resistive sensor Capacitive sensor Inductive sensor LVDT Problem solution Piezoelectric sensor Electromagnetic spectrum Radiation thermometer
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∵ ρ : Specific resistance
1. Strain gage : Changes in L & ρ2. Force sensing resistor : Changes in
A3. Thermister : Changes in
temperature4. Potentiometer : Changes in Length
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R
F
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RCeramic
NTC thermister(Negative temperature coefficient)
PTC thermister(Positive temperature coefficient)
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R
E [ v ]
R s
+ Vout- Vo, Vs, F, T : Non linear
E [ v ]
RR s
-
+
A )
B )
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C )
Bridge circuit
D )
Linearization
Rp
Rs
Rs
Rp
R
Linear range
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x
A
εRMost capacitive sensor is based on changes in x.
Capacitive sensor
Inductive sensor
1.Self Inductance 2.Mutual Inductance3.Difference
Inductance
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LVDT(Linear Variable Differential Transformer)a
b
c
d
e
fx=0
x=-D
x=D
Primary coil
x= δ
x=-δ
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Mutual Inductance Sensor
Magnetic core
+Vo-
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
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x=0
x=-D
x=D
D=20mm, 2D=40mm
Method 1: Rectifier + LPF
Full wave
rectifier
LPF
t
V(t)
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Method 2: Phase-Sensitive demodulation
Vo(t)
x(t)·Vo²(t)
x(t) = sin(2π· 1000t)
LPF(Low Pass Filter)
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
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x
q : Charge , x : Deflection
That means piezoelectric sensor has no DC response.
Fig. piezoelectric sensor
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Ri(t)
Vs(t) = R*i(t)
i=0
i=0
+
IA
-
Vo(t)
1)
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2)
i(t), Current flow
-
IA
+
Vo(t)
R
C
0V
Change Amplifier
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f
|H|
k/c
fc
= 1/2πRC
If you plan to use the piezoelectric sensor, for measuring pulse, the lowest frequency of pulse, signal is assumed to be 0.1Hz
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