Transcript MEDICAL INSTEUMENTATION . 동서의료공학과 2005200444 정 진 웅 A kinds of resistive Sensors. 1. 2. 3. 4. Strain gage Potentioneter FSR Thermister and so on.

MEDICAL
INSTEUMENTATION
.
동서의료공학과
2005200444 정 진 웅
A kinds of resistive Sensors.
1.
2.
3.
4.
Strain gage
Potentioneter
FSR
Thermister
and so on.
1. (Axial) stress
y
x
M
f  mg
On the surface
The (average) force per unit area is
denoted as σ
F N
  [ 2]
A m
“stress”
(cf = pressure)
F is sometimes called
“load”
2. Strain
L
F

 m
[
L m
]
Strain is unitless
Because unit N is
divided with unit N

F
3.
 &  curve
Brittle material (ex, glass)

Non linear area
(ultimate stress)
rapture
linear area
0

3.
 &  curve
ductile material (ex, Al, steel)

n
 ys
rapture
: Al
 pt

Elastic area
Plastic area
3.
 &  curve
ductile material (ex, Al, steel)

 pt
rapture
: steel

Elastic area
For elestic region (linear region) (σ ≤ σPL)
  E
F
 
A
 

L
4. Cantilever

L
F
neglesible
  E
F

 E
A
L
AE
F
  AE 
L
E : constant
A & L : almost constant
4. Cantilever
F
L
L 
F  
  E
F

 E
A
L
5. Strain gage
substrate
Electrical wire
Flexible material
From now on, this wire have a
length L and surface area A
Surface
Area ‘A’
L
L R  L A L



R
 strain

L
A
A R
L
6. Gage factor
R
R
G
L
L
R


R  1  2 
L

L
For metal strain gage G : 0 ~ 1.6
For semi-conductor strain gage G : 100~179
(high temperature coefficient)
7. Problem 3
Q3)
4 metal strain gage that have gage factor 4 are set up
in a machine.
And gage 1 and 2 is increased length ΔL on the force
that pull down machine, gage 3 and 4 is decreased
length ΔL, and there is relationship ΔL/L = k * f (k is
constant).
Design by bridge circuit that out voltage
proportionate force. Represent out-voltage by force.
Drive voltage is dc 5v
7. Problem 3 solution
R3
R2
R4
7
3
+
V+
OS1
OUT
5Vdc
R1
R4
R2
1k
1k
2
R1
R  R
Va 
5 
5
R1  R3
2R
R4
R  R
Vb 
5 
5
R2  R4
2R
-
4
OS2
V-
1
6
8
2R
R
Vo  Av (Va  Vb )  Av
 5  5 Av
2R
R
 5 Av 10 
Vo  50Av kF
L
 50 Av kF
L
8. Problem 4
Q4)
I plan to make a force measurement system using that 2 p-type Si strain
gage with gage factor 100and 2 n-type Si strain gage with gage factor100.
I attach 2 p-type Si strain gage on the cantilever and 2 n-type Si strain
gage under the cantilever.
(a)Design the circuit that bridge circuit with 4 strain gage and amplify the
bride circuit’s output. And, find each strain gage type. Drive voltage is dc
1v.
(b) When forced on the cantilever, we suggest cantilever change with
same length between upper surface and under surface. Strain gage’s
maximum length change rate is ±0.05%, strain gage’s non load resistor is
200 ohm. Find the benefit to change the result output from 5v through
force.
(c) Suggest the method to do calibration that force measurement.
8. Problem 4 solution
R3
R4
7
3
+
V+
OS1
OUT
5Vdc
2
R1
R2
1k
1k
Va 
R1
R  R
E 
E
R1  R3
2R
Vb 
R4
R  R
E 
E
R2  R4
2R
-
4
OS2
V-
1
6
8
R
 5v  Vo  Av E
 5v
R
L
 max 
 0.0005
L
R  200
8. Problem 4 solution
R
L
Vo  Av E
 Av  5  G
R
L
Vo,max  Av  5 100 0.0005 Av  0.25  5V
5
 Av 
V  20V
0.25
(c) To do calibration, Use a program ‘matlab’ with matrix transformation.
Then you can do calibration
9. Problem 6
Q6)
Under pressure sensor, 2 p-type Si strain gage with gage factor +100
and 2 n-type strain gage with gage factor -100 are attatched on the
diaphragm. When forced with pressure on the diaphragm, same strain is
made on the strain gage, then that sensitivity is 10⁻⁵ %/mmHg, when not
forced with pressure, strain gage’s resistor is 50ohm. Suggest that
relationship between pressure and strain is linear.
(a)When pressure change between 0 ~ 500mmHg, find the change with
p-type and n-type Si strain gage’s resistor values.
(b) Design bridge circuit composed 4 strain gage and check on the figure
location of each strain gage.
(c) Make a bridge circuit’s drive voltage is dc 1v, and add measurement
amplifier to change result output between 0 ~ 1v, then find the benefit.
9. Problem 6 solution
I am so, so sorry professor Mr.Woo.
I don’t know how to solve it.
Without fail, I will find the method.
Sorry..
감사합니다