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
Top Related