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Applied Electronic Circuit. #7 . 2007102832 김명준. Instrumentation Amplifier : IA. High Input Impedance Low Output Impedance Accurate and Stable Gain (1 ~ 1000) High CMRR . Instrumentation Amplifier : IA. 이득가변. For CMRR Tuning. Instrumentation Amplifier : IA. Differential Mode Input –

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applied electronic circuit

Applied Electronic Circuit

#7

2007102832 김명준

instrumentation amplifier ia
Instrumentation Amplifier : IA

High Input Impedance

Low Output Impedance

Accurate and Stable Gain (1 ~ 1000)

High CMRR

instrumentation amplifier ia1
Instrumentation Amplifier : IA

이득가변

For CMRR Tuning

instrumentation amplifier ia2
Instrumentation Amplifier : IA

Differential Mode Input –

Differential Mode Output Amplifier

One Chip Instrumentation Amplifier

AD620 oretc

dual op amp instrumentation amplifier
Dual OP AMP Instrumentation Amplifier

단점

신호가 소자 통과 시 time delay 발생!

이 에 비해 time delay가 크다.

→ phase distortion 발생

Gain 조절 쉽지 않다

ground loop
Ground loop

Stray capacitor

실제로는 도선에 연결된 Capacitor가 아닌

매질을 통해 연결된 가상의 Capacitor

도선 자체 저항

ground loop1
Ground loop

, but is possible.

CMRR 감소의 원인

R 감소 방법 : lead wire를 짧고 굵은 선으로!

shield cable
Shield Cable

도자기

절연체

도체

cable

coaxial cable

절연체

Triaxial cable

shield
Shield

220V

60Hz

도체 (등전위면)

Shield(차폐) : 적절한전압 유지

Chassis

Grounded Shield(접지 차폐)

shield1
Shield

220V

60Hz

Shield 가능

+

-

IA

Shield 불가능

Ground Shield

오히려 더 나빠진다→ 원치 않는 DM current 더 생겨

전원 전압에 의한 interference 제거

Leakage Current increased

shield2
Shield

Cable에 흐르는 전압과 같은 전압을 Shield에 Drive

-

+

+

-

IA

-

+

Active Shield

(Driven Shield)

shield3
Shield

Active Shield& Ground Shield

-

+

전체가 Ground Shield

transducer bridge amplifier
Transducer Bridge Amplifier

Resistive Sensor

Temperature ; Thermister, RTD

Light ; Photoresistor

Strain ; Straingage

Pressure ; piezo resistive sensor

물리량의 변화 -> 저항의 변화 -> 전압의 변화

bridge circuit
Bridge Circuit

일 때,

→ Balanced

AC 사용할 수 있음

Capacitive sensor

Inductive Sensor

conduction in metal conductor
Conduction in Metal (Conductor)

e-

e-

e-

e-

mobility

T↑,

+

+

+

+

e-

e-

e-

e-

+

+

+

+

n; 자유전자의 부피밀도

e-

e-

e-

e-

전류밀도

+

+

+

+

=

conductivity

conduction in metal conductor1
Conduction in Metal (Conductor)

T[s] 동안 L[m] 이동한다면,

N개의 Free electron

A

L

conduction in metal conductor2
Conduction in Metal (Conductor)

온도계수(Temp wett.)

conduction in metal conductor5
Conduction in Metal (Conductor)

Ex. Pt RTD

To prevent self heating

최종적으로 0.1V/℃의출력을 얻기 위하여

margin

T: 0~100℃ → : 0~10V

Ω

conduction in metal conductor6
Conduction in Metal (Conductor)

Ex. Pt RTD

근사식이 아닌 식을 사용하면, 근사식인 경우에 비해 약 0.26℃ 차이 발생

bridge balancing
Bridge Balancing

Bridge Arm에 흐르는 전류를 제어 → 민감도 조절

1% 저항, 5% 전원 사용

0-2V

Balancing (영점 조정)

2mA

14V

1mA

1mA

14-16V

(xA)

전원 : V 변동

bridge balancing1
Bridge Balancing

To be safe,

라 가정

280 변화

ⓐ점의 전압=14V

To be safe,

전압=0~2V

Choose

에 흐르는 전류= 2mA

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