Applied electronic circuit
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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

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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 conductor3

Conduction in Metal (Conductor)

Ex. Pt RTD


Conduction in metal conductor4

Conduction in Metal (Conductor)

Ex. Pt RTD

(xA)


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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