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Medical Instrumentation II. Resistive Sensor Strain gage : changes in L & ρ Force sensing...
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Transcript of Medical Instrumentation II. Resistive Sensor Strain gage : changes in L & ρ Force sensing...
Medical Instrumentation II
Resistive Sensor
Strain gage : changes in L & ρ Force sensing resistor : changes
in A Thermistor : changes in L Potentiometer : changes in L
Medical Instrumentation II
FSR(Force sensing resistor)
Medical Instrumentation II
FA & F is proportion.R & 1/F is inverse proportion.
RThermistor
R
F
R
T
R∞
NTC(Negative Temperature Coefficient)
R s R
O PAMP
+
-
O U TIA
Vo = - R/Rs E
E
Design.
Medical Instrumentation II
R
R s
-
+
Vo
(A)
(B)
oV
ERR
RVs
so
V0 vs F or T : Non - linear
V10V dc
U 1
O PAMP
+
-
O U TE[v]
S3
R1 S2
S4
reference
in = 0
ip = 0
IAVa Vb
Medical Instrumentation II
(C) Bridge circuit
(D) Linearigation R p
R s
R = RsRp / Rs + Rp
Rs
Rp
Linear RangeR
Capacitive Sensor
Medical Instrumentation II
A
x xAC ko
k
Most capacitor sensor are based on changes in x
Inductive Sensor Self Inductance Mutual Inductance Differential Inductance
Medical Instrumentation II
(1) Self Inductance
x
F(2) Mutual Inductance
-bVs Vo
+a
- D
Medical Instrumentation II
(3) LVDT (Linear Variable Differential Transformer) D
X = 0
b
a c
d
e
δ
- δ
efcdcfo VVVV
Vs Vo
(b) When core is at X = + δ
(a) When core is at X = 0
(c) When core is at X = + δ
Vcd is Blue, Vef is Red and Vo is Black
Vo = 0
f
Problem 13.
Using LVDT, A object that is a reciprocasting motion verticality direction measure location. This is y(t), changing by next page figure. 1st coil’s voltage is V(t) = sin(2π x 1000t) [v].
(a) Design the LVDT output signal in 0 ~ 10ms. 2nd coil’s phase isn’t delay, Suppose LVDT
is linear in ± 20mm. (b) Write verticality direction y(t) by LVDT output signal. (c) Write calibration method for output voltage represent [mm] unit
Medical Instrumentation II
Problem 13. LVDT
Medical Instrumentation II
40mm
F
X=20mm
X=0
X=-20mm
20mm
-20mm 5ms 10ms
180 ̊ Phase change
])[10002sin()( vttVs
msTkHzf 1,1
t
y(t)
Method 1. Rectifier + LPFNo Phase
change!
RC
FWR LPF V(t)
Vo(t)
V(t)
t
Medical Instrumentation II
Method 2. Phase-sensitive demodulation
Medical Instrumentation II
X LPFVo(t
)
sin(2πx10³t)
V (t)
IVo(t)I
t
g X g
Matlab 3. 5~10ms 사이에 0.01ms 씩 샘플링하여
그래프 표현 filter 함수 배열 사용 .
Medical Instrumentation II
Piezoelectric sensor
xkxeChq )arg(
dttdxk
dttdqAi )()(][
I A
O PAMP
+
-
O U TR Vo(t)x(t)
(1)
Medical Instrumentation II
O PAMP+
-
O U T
C(2)
CjR
CjR
IIo
1
1
RCjRj
RCjRIIo
11
I H I
Tfc = 1 / 2πRC
Medical Instrumentation II
If you plan to use the piezoelectric sensor for measuring pulse the lowest frequency of pulse. Signal is assumed to be 0.1Hz.
Medical Instrumentation II