MEDICALINSTEUMENTATION.

동서의료공학과2005200444 정 진 웅

A kinds of resistive Sensors.

1. Strain gage2. Potentioneter3. FSR4. Thermister

and so on.

1. (Axial) stress

M

y

x

On the surfaceThe (average) force per unit area is

denoted as σ

mgf ][2m

N

A

F

“stress”(cf = pressure)

F is sometimes called “load”

2. Strain

F

F

L

][m

m

L

Strain is unitlessBecause unit N is divided with unit N

3. & curve Brittle material (ex, glass)

rapture

Non linear area(ultimate stress)

linear area

0

3. & curve ductile material (ex, Al, steel)

n

ys

pt

Elastic area

Plastic area

rapture

: Al

3. & curve ductile material (ex, Al, steel)

rapture

pt

Elastic area

: steel

For elestic region (linear region) (σ ≤ σPL)

EA

F

L

4. Cantilever

L

F

neglesible

EL

EA

F

AEL

AEF E : constant

A & L : almost constant

4. Cantilever

FL

L

F E

LE

A

F

5. Strain gage

substrate

Electrical wire

Flexible material

From now on, this wire have a length L and surface area A

L

SurfaceArea ‘A’

A

LR

A

A

L

L

R

R

strainL

L

6. Gage factor

LL

RR

LLR

RG

21

For metal strain gage G : 0 ~ 1.6For 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

5V dc

R 1

1k

R 2

1k

R 3 R 4

+3

-2

V +7

V -4

O U T6

O S 28

O S 11

52

5

52

5

42

4

31

1

R

RR

RR

RV

R

RR

RR

RV

b

a

R

RA

R

RAVVAoV vvbav

55

2

2)(

kFAL

LA vv 50105

kFAV vo 50

R2

R4

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 factor-100. 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

5V dc

R 1

1k

R 2

1k

R 3 R 4

+3

-2

V +7

V -4

O U T6

O S 28

O S 11

ER

RRE

RR

RV

ER

RRE

RR

RV

b

a

2

2

42

4

31

1

vR

REAVv vo 55

200

0005.0max

RL

L

8. Problem 4 solution

L

LGA

R

REAV vvo

5

VAAV vvo 525.00005.01005max,

VVAv 2025.0

5

(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