Medical Instrumentation Ⅱ
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Transcript of Medical Instrumentation Ⅱ
X
Y
M
F = MG
Fig1.1
AA = X·Y
“On the surface, the (average) force per unit area is denoted
as σ. F is sometimes called ‘load’.”
A
F : “Stress” (solid material), pressure – liquid, air …
unit: [N/ ]2m
▶ (Axial) Stress
▶ σ & ε curve 1. Brittle material (glass)
σu
linear region(elastic region)
rupture
nonlinear region
σu : ultimate stress
ε
“Not linear over a wide
range.”
Fig1.3
▶ σ & ε curve 2. Ductile material (Al)
σu
σys
σPl
elastic region
plastic region
ruptureσys : Yield stress
σPl < σys < σu
Fig1.4
▶ σ & ε curve 2. Ductile material (steel)
σPl
elastic region
for elastic region (linear region)
(σ ≤σPl)
rupture
σ = E·ε
Fig1.5
E: Young’s modulus(modulus of elasticity)
L
FWall
Fig1.6
δ
Negligible
▶ Cantilever
LE
A
F
σ = E·ε
AL
AEF £ε
“If you know ε, you can find force.”
E: constantA&L are almost constant
▶ Strain gage
“A strain gage is a device used to measure the strain of an object. The gage is attached to the object by a suitable adhesive. As the object is deformed, the foil is deformed, causing its electrical resistance to change.”
Fig1.8
L
A ρ
ρ : resistivity
Fig1.11
▶ Resistance
“The Length is stretched,
ρ ,L,A are changed.But volume is
constant.”
A
LR
A
LR
A
LR
LA
RL
AL
R
2A
L
A
R A
A
LRA
2
AL RRRR
AA
LL
AA
LR
2
A
A
L
L
R
R
Strain ε
L
L 2
=
LD
Fig1.11
∆L
D- ∆D
▶ Poisson’s ratio, μ
L
L
D
D
D: diameter
L
L
R
R
)21(
piezoresistive effect
dimensional effect
▶ Problem
Pi
Po
catheterliquid sensor
diaphragm
There are two p-type Si strain gage and two n-type Si strain gage.Strain gage’s sensitivity is . When pressure is not applied, it’s resistance is 50Ω.
mmHg/%10 5
▶ Answer(a) If pressure vary from 0 to 500mmHg, what is each strain gage’s resistance?
☞ p-type strain gage’s resistance : 50+ ΩP510
☞ n-type strain gage’s resistance : 50- ΩP510
When pressure is not applied, it’s resistance is 50Ω. And sensitivity is . therefore,mmHg/%10 5
▶ Answer(b) Draw bridge circuit. And declare each strain gage’s position.
S1
S3
S2
S4
S1S2
S3S4
a b-
+
1V
Vo
▶ Answer(c) Design flowing circuit. Vdc = 1V, Vo = 0~1V, Av = ?
1131
1
RRRR
RR
RR
RVa R
RR
2
1142
2
RRRR
RR
RR
RVb R
RR
2
VbaO AVVV )(
VAR
R)(
When Pressure(∆R) is zero, Vo=0V.When P=500mmHg,
VAV VO 150
50010 5
410 VA