Chuong1-Cam Bien&Ung Dung

Gio trnh in T ng Dng 1

Chng 1: CAM BIEN VA NG DUNG

1.1: Gii thieu chung:

Cam bien c nh ngha la mot dung cu thu nang lng t mot he thong va chuyen thanh mot

dang nang lng khac phat en mot he thong khac.

nh ngha mot cach m rong cam bien la mot dung cu c tac ong bi mot nang lng vao t

mot hoac nhieu moi trng va lan lt phat ra tn hieu tng ng en mot hoac nhieu he thong phat

khac. No cung cap 1 tn hiu hu dung ap ng vi mot ai lng o lng cu the nao o, v du nh ai

lng vat ly, c hoc, hoac mot gia tr thch hp nao o.

Nang lng phat ra t nhng he thong nay co the la ien, c hoac am.

ac tnh ien cua ngo ra cam bien tuy thuoc vao nguyen ly c ban thiet ke no. Tn hieu ra co the

la tng t, so hoac tan so ieu che.

Co the phan thanh hai loai cam bien ien va cam bien c.

Cam bien ien la mot dung cu cam ai lng vat ly ,c hoac quang o c chuyen thanh tn

hiu ien di dang ien ap / dong ien ty le vi gia tr o ngo vao. Mot cam bien ien phai co cac

thong so sau:

1- Tuyen tnh: quan he gia ai lng vat ly va tn hiu ien ngo ra phai tuyen tnh.

2- o nhay:c nh ngha la s bien thien tn hieu ien tren bien thien 1 n v ai lng vat ly

(v du: V/o C oi vi cam bien nhiet). o nhay cao luon la yeu cau oi vi cam bien.

3- Dai ong: tam hoat ong cua cam bien phai rong e cho phep no c s dung trong cac ieu

kien o gia tr tam rong.

4- Kha nang lap lai: quan he ngo vao/ra cua cam bien phai c xac nh co nh trong thi gian

dai. ieu nay am bao kha nang hoat ong tin cay cua cam bien.

5- Kch thc vat ly: cam bien phai co trong lng va the tch cang nho cang tot khong gay tr ngai

ve kch thc trong he thong.

S tien li cua cam bien ien c tom tat nh sau:

1- De dang khuech ai/ suy giam tn hieu ien.

2- Bo qua anh hng cua quan tnh khoi lng.

3- Bo qua anh hng cua ma sat.

4- Ngo ra co the c hien th va ghi lai t xa so vi v tr at cam bien.

5- Ngo ra co the c hieu chnh ap ng yeu cau hien th hoac ieu khien. Bien o tn hieu co the

chuyen di dang ien ap / dong ien.

6- Tn hieu co the c x ly hoac tron e tao c bat ky s ket hp tn hieu ngo ra cua cac cam

bien giong nhau hoac cac tn hieu ieu khien.

7- He thong ien/ ien t c kiem soat bi mc nang lng rat be.

8- Tn hieu ien ngo ra co the de dang s dung, phat hoac truyen i cho muc ch o lng ieu

khien.

Cam bien ien co the phan thanh 2 loai chnh la cam bien chu ong va cam bien thu ong.

Cam bien chu ong phat ra tn hieu ien trc tiep ai lng vat ly va khong can s dung

nguon ngoai khi hoat ong. Cam bien chu ong la loai t phat tn hieu, ngha la no lam viec

theo nguyen ly chuyen oi nang lng va phat tn hieu ngo ra tng ng.

V du tieu bieu ve cam bien chu ong la cam bien nhiet cap nhiet ien hay cam bien ap ien, phat

ra sc ien ong ngo ra khi co tac ong thay oi ve nhiet o hoac lc.

Cam bien thu ong hoat ong theo cac nguyen ly kiem soat nang lng,can phai s dung

nguon ngoai. No phu thuoc vao s thay oi cac thong so ien R,L,C.


- Cac cam bien thu ong tieu bieu nh cam bien sc cang thay oi ien tr theo ap lc hay

thermistor thay oi ien tr theo nhiet o.

Cam bien ien c s dung hau het e o cac ai lng phi ien. Vi muc ch nay phai s

dung phan t phat hien hay cam ng, chuyen oi ai lng vat ly sang o dch chuyen /bien thien. o

dch chuyen /bien thien tac ong vao mot cam bien ien hoat ong nh la cam bien th cap va cho tn

hieu ien ngo ra. ai lng ien ngo ra co the la dong ien, ien ap, tan so da tren cac thong so thay

oi R, L C.

Mot cach tong quat, cam bien chuyen 1 tn hieu phi ien ra thanh 1 tn hieu ien co the xem nh

gom 2 phan, phan cam va phan bien.

Phan cam/ phat hien la phan ap ng vi mot hien tng vat ly hoac tao mot thay oi mot hien

tng vat ly. ap ng cua phan cam phai cang giong vi hien tng vat ly.

Phan bien chuyen oi ap ng cua phan cam thanh tn hieu ien ngo ra, hoat ong nh cam

bien th cap.

Cam bien co the c phan loai thanh nhieu loai khac nhau tuy theo nguyen ly s dung phan t

cam bien e chuyen oi hien tng vat ly sang tn hieu ien, hay theo ac tnh ng dung cua

cam bien.

* Phan loai theo phan t cam bien

1- ien tr

2- ien cam

3- ien dung

4- ien t

5- Ap ien

6- Phat quang

7- Cam quang

8- Phan ap

9- Nhiet ien

10- Phat tan so

* Phan loai theo ac tnh &ng dung:

1- Cam bien quang

2- Cam bien nhiet

3- Cam bien v tr va dch chuyen

4- Cam bien bien dang

5- Cam bien van toc

6- Cam bien lc

7- Cam bien ap suat

8- Cam bien mc chat long

1.2: Cam bien quang:

Trong phan cam bien quang,ta se khao sat cau tao, hoat ong, ac tnh cac loai cam bien thong

dung nh quang tr, photo diode, photo transistor, en nhan quang ien va cac ng dung tieu bieu.

Cac cam bien nay hoat ong theo cac hieu ng quang dan va hieu ng rao quang the.

1.2.1 Quang tr:

Cau tao, ky hieu:

Hnh 1.1 Nguyen ly cua cam bien quang dan

-


Quang tr lam viec theo hieu ng quang dan. Tren mot thanh ban dan nhieu tap chat n tiet dien

A, chieu day L, co mot ca so e anh sang co the chieu xuyen qua.

Bnh thng khi che anh sang hay at quang tr trong bong toi, ien tr quang tr hai au 1-2

rat cao , khi co anh sang chieu vao, se cung cap nang lng e tao ien t t do vi mat o tang ty le

cng o anh sang chieu vao ca so . Ket qua la neu cap mot ien the mach ngoai hai au 1-2,se

tao dong ien qua quang tr va ien tr cua quang tr cung se giam ty le theo cng o anh sang

chieu vao ca so.

Hnh 1.2: a) Cau tao c ban quang tr

b) Ky hieu quang tr

- Hnh 1.2 a minh hoa cau tao c ban mot quang tr

- Hnh 1.2 b la ky hieu cua quang tr. Hai mui ten bieu dien anh sang chieu vao ca so.

- Cac vat lieu s dung lam quang tr:

+ Vat lieu a tinh the : CdS, CdSe, CdTe

PbS, PbSe, PbTe

+ Vat lieu n tinh the: Ge, Si, themtap chat Au, Cu, Sb, Zn

SbIn, AsIn, PIn, CdHgTe.

Moi loai vat lieu se ap ng tot nhat vi tan bc song anh sang thch hp.

ac tnh quang tr:

Ta goi RC0 la ien tr toi , ngha la ien tr ng vi

ca so b che chan hoan toan khong cho anh sang

chieu vao

RC0 khoang 104-109 @ 25oC vi loai PbS, CdS,CdSe

RC0 khoang 10 - 103 @ 25oC vi loai SbIn, SbAs,CdHgTe

RC la ien tr khi co anh sang chieu vao ca so. RC giam

rat nhanh theo chieu tang cua cng o anh sang nh

ng bieu dien tren hnh 1.3.

Hnh 1.3: Bien thien ien tr theo cng o anh sang.


- Co the bieu dien mach tng ng cua quang tr gom RC0 //RCp trong o RCp la ien tr b anh

hng bi anh sang toi theo hieu ng quang ien: .aRCp (1.1)

a: phu thuoc vao vat lieu, nhiet o va pho anh sang ti.

: quang nang anh sang ti (quang thong )(W)

= 0,51: he so truyen at

Hnh 1.4: Mch tng ng quang tr

.

..

0

0

0

0

aR

aR

RR

RRR

C

C

CpC

CpC

C (1.2)

Trong thc te: thng RCp RC0 , ta co:

.aRC (1.3)

*Nhan xet: Bien thien ien tr theo cng o anh sang khong tuyen tnh, co the tuyen tnh hoa tng

phan bang cach mac them mot ien tr song song vi quang tr (xem phan mach tao va x ly tn hieu)

Ga tr ien tr quang tr con phu thuoc vao nhiet o va ien ap ap len no.

o nhay: Theo hnh 1.4, ien dan cua quang tr:

CpCC GGG 0 (1.4)

Vi GC0=1/RC0 va GCp=1/RCp=(1/a).

Goi V la ien ap tren RC va I la dong qua RC:

I= GC.V = GC0.V+GCp.V = I0+Ip (1.5)

Vi GC0.V=I0: dong qua quang tr toi

Va GCp = Ip: dong tao ra do hieu ng quang ien

Thong thng: I0


- Quang tr ty le phi tuyen vi quang thong, trng hp ac biet =1 quan he gan tuyen tnh, ch

ap dung oi vi tn hieu nho, ngha la quang thong bien thien be.

- Quang tr ty le vi ap V at tren no, tuy nhien neu tang ap dan en mat mat cong suat va nhiet

o tang gay giam o nhay quang tr.

ap ng thi gian va tan so:

- Thi gian ap ng va tan so ap ng phu thuoc vao vat lieu la chu yeu,

- Thi gian ap ng la thi gian thay oi gia tr ien tr khi cng o anh sang vao bien thien.

- Thi gian ap ng 0,1 s oi vi loai SbIn, AsIn, CdHgTe, va

0,1 100 ms oi vi loai PbS, PbSe, CdSe.

Tan so ap ng la tan so thay oi o nhay quang tr theo tan so bien thien cng o anh sang. Fc

= 102 105 Hz.

ng dung tieu bieu:

- Do ac tnh phi tuyen cua quang tr theo cng o anh sang nen ngi ta thng ch s dung

quang tr trong cac ng dung ve nhan dang mot mc cng o anh sang .

- V du: o mc cng o anh sang, ieu khien theo mc cng cng o anh sang.

Hnh 1.5 minh hoa cac dang mach s dung quang tr ong m/ r le theo mc cng o anh sang.

Hnh 1.5: S dung quang tr ong/ m r le theo cng o anh sang.

1.2.2: Photo diode:

Cau tao, ky hieu:

Hnh 1.6 a) Rao the tiep xuc PN b) Ky hieu photo diode

Khi tiep xuc PN cha co phan cc ngoai, xuat hien mien ngheo tai vung tiep xuc va ien trng

Eb sinh ra rao the Vb, dong ien qua tiep xuc PN gom:

- Dong ien thuan do cac hat tai a chuyen ong t PN (ien t t ban dan N va lo trong t ban

dan P ) xuat hien khi co nguon nang lng ngoai hoac ien ap ngoai kch thch thang c rao

the Vb.

- Dong ien nghch do cac hat tai thieu chuyen ong t N sang P (ien t t ban dan P va lo trong

t ban dan N) xuat hien do ien trng Eb


- Neu ap vao mot ien ap phan cc nghch cang lam tang Eb va Vb va dong nghch cang tang neu

hat tai sinh ra nhieu. ay la nguyen ly lam viec cua photo diode.

- Khi co anh sang chieu vao vung tiep xuc photo diode se sinh ra cac hat tai t do la ien t va lo

trong.Neu phan cc nghch, cac hat tai nay se chuyen ong tao dong ien nghch qua diode tang

ty le theo cng o anh sang chieu vao ca so .

Goi Vd va I lan lt la ien ap va dong ien tren diode:

00 exp IKT

qvII d

(1.9)

Do vd


Trng hp vd kha ln, so hang ham mu co the bo qua :

Ir = Io + Ip (1.13)

Va trong trng hp cng o anh sang u manh:

Ir = Ip (1.14)

T hnh 1.7a, ta co phng trnh ng tai :

m

d

m

sr

R

v

R

EI (1.15)

Lu y: Vr = Ir x Rm ty le tuyen tnh vi theo Ir.

- Hnh 1.8 la mach tng ng photo diode

Hnh 1.8 Mach tng ng photo diode

Is = Io + Ip : nguon dong

rd: ien tr ong tiep xuc phan cc nghch 1010

rs: ien tr tiep xuc c vai chuc , rs Rm co the bo qua

Cd: ien dung tiep xuc, Cd c hang pF va giam khi tang vd.

2- Mode rao quang the:

Trong mode nay photo diode khong can cap nguon ngoai va no ong vai tro mach phat ap trong

trng hp h mach va phat dong trong trng hp ngan mach.

+ H mach Vco: ap tren tiep xuc la vb Ir = 0

0exp 00

p

b IIKT

vqI (1.16)

0

1I

ILog

q

KTv

p

b (1.17)

Vi: )exp(..

)1(0 X

ch

RqI p

Do h mach nen vb = Vco, do o:

0

1I

ILog

q

KTV

p

co (1.18)

Trng hp cng o anh sang that yeu:

0

0I

I

q

KTVII pcop (1.19)

Nhan xet: Vco ty le tuyen tnh Ip hay cng o anh sang.

Trng hp cng o anh sang manh:

0

0I

ILog

q

KTVII

p

cop (1.20)

Vco ty le vi ham log cua cng o anh sang.

Trng hp Rm rd : RmIr = Vd (1.21)


+ Ngan mach Isc :trng hp Rm


hnh 1.10a, ap ng tuyen tnh:

CCm IRV 0 (1.24)

hnh 1.10b , ap ng loga:

coVR

RV

1

20 1 (1.25)

1.2.3: Photo transistor:

Nguyen ly lam viec:

Ve cau tao, photo transistor giong nh transistor thong thng, ch co khac mien B c kch

thch bi anh sang ngoai. Khi phan cc photo transistor cung tng t nh cach phan cc transistor thong

thng, v du nh hoat ong che o khuech ai,tiep xuc B-C phan cc nghch,tiep xuc B-E phan cc

thuan.Mach ien CE cua photo transistor cung nh mach CE transistor thong thng,ch co ieu lu y

la khong can phai am bao tiep xuc BE phan cc thuan(VBE =0,6V (Si)) va co the khong can phan cc

BC trong mot so trng hp. Khi co anh sang chieu vao mien B , phat sinh dong IB tng t nh photo

diode , dong IB sinh ra t tiep xuc BC cua photo transistor.

Hnh 1.11: a) Mach phan cc photo transistor

b)Mach tiep xuc BC tng ng nh photo diode.

Ta co: Ir = Io+Ip

Ic = (+1) Ir = (+1) Io + (+1) Ip (1.26)

: HSK dong mach EC

(+1)Io = Ico ,dong toi photo transistor

(+1)Ip = Icp dong Ic phu thuoc vao anh sang ti.

Mach tng ng photo transistor nh hnh 1.12:

Hnh 1.12 Mach tng ng photo transistor

f thap , bo qua Cbe va Cbc ta co:

Vm = -(gm vbe +Ip )Rm (1.27)

Vi: vbe = rbe Ip va gm = /rbe

Vm = -( +1)Ip.Rm (1.28)

Nh vay f thap photo transistor tng ng nh mot nguon dong (+1)Ip .


- Dong ro Ico hay dong Ic toi 25oC khoang 10-8 10-9 A tuy thuoc vao ien ap tren CE va nhiet

o. Co the giam dong Ico bang cach phan cc cc B bang mot ien tr va u nho.

- ap ng tan so:

mmcbebeb

cRgCC

gf

1(2 ''

'

ng dung tieu bieu:

Co the ng dung photo transistor trong cac mach khuech ai hoac giao hoan cach ly tn hieu va

hoat ong nh transistor thong thng.

Hnh 1.13: Cac mach s dung photo transistor giao hoan

Hnh 1.13 a) Photo transistor kch trc tiep r le

Hnh 1.13 b) Photo transistor mac darlington vi 1BJT keo rle

Hnh 1.13 c) Photo transistor lai cong logoc

Hnh 1.13 d) Photo transistor kch cc G SCR.

Hnh 1.14 a) - Photo transistor kch mach BJT mac BC.

Hnh 1.14 b) - Photo transistor va OPAMP chuyen dong thanh ap

Hnh 1.15: Cac mach photo transistor lam viec tuyen tnh

Hnh1.15 a) Mach o thong lng(flux)

Hnh 1.15 b) Mach K CC co phan cc B


Hnh 1.15 c) Mach K CC loai dong ro Ico.

1.2.4:en nhan quang ien:

en nhan quang ien bao gom mot ong thuy tinh chan khong cha cathode phat quang, mot

anode va nhieu ien cc trung gian goi la dynode, moi dynode sau c phan cc ap cao hn so vi

dynode trc.

Hnh 1.16: Cau tao c ban en nhan quang ien

Khi anh sang chieu vao cathode,ien t phat ra t cathode c hut en dynode th 1. ay goi la

phat xa th cap. Khi e- chuyen ong vi toc o cao ap vao vat lieu thch hp, vat lieu se phat ra mot

lng ln e- nhieu hn lng e- ap vao no. Do phan cc cac dynode sau cao hn dynode trc nen toc

o va so lng e- ngay cang tang cho en khi e- en anode.He so khuech ai co the t 105 en 109,o

nhay anh sang co the t 1A/lumen en 2000A/lumen,dong anode co the t 100A en 1mA.

Do o nhay anh sang rat cao,chang han vi o nhay 100A/lumen ch can 10-5 lumen se tao ra

mot dong anode 1mA.en nay b anh hng bi t trng nen ben ngoai phai co vo boc chong nhiem

t.

1.3: Cam bien nhiet:

Cac loai cam bien nhiet thong dung co the phan loai thanh 2 dang :

Cam bien nhiet ien tr: gom nhiet tr kim loai, nhiet tr ban dan (thermistor) hoat ong theo

nguyen ly thay oi ien tr theo nhiet o.

Cam bien nhiet ien ap: gom cap nhiet ien (thermocouple),tiep xuc P-N, vi mach hoat ong

theo nguyen ly thay oi ien ap theo nhiet o.

1.3.1: Nhiet tr kim loai:

Nhiet tr kim loai co he so nhiet tr dng, cau tao gom mot day kim loai quan xung quanh mot

truc s cach ien va co vo boc bang kim loai dan nhiet tot ben ngoai. Kim loai thng c s dung la

day platin hoac nikel.

Hnh 1.17: Cau tao nhiet tr kim loai.

1- Nhiet tr Platin: Tam o cua nhiet tr platin trong khoang 200oC 650oC, o phan giai co the

en 0,1oC va quan he ien tr / nhiet o kha tuyen tnh

Bieu thc quan he ien tr / nhiet o cua nhiet tr platin:


R(T) = Ro [1+AT+BT2+C(T-100)T3](T= 0oC) (1.29)

Trong o: A= 3,90802 x10-3/oC

B = -5,80195 x10-7/oC2

C = -4,27350 x10-12/oC4 vi T< 0oC va C= 0 khi T>0oC

Ro: ien tr T= 0oC

Trong thc te ngi ta goi cac loai ien tr Pt50,Pt75,Pt100 tng ng Ro = 50, Ro=75,

Ro = 100,at tai nhiet o T= 0oC.

Trng hp nhiet o thap T100oC, AB, C=0:

Ta co: R(T) = Ro[1+3,9 x10-3T] (1.30)

2-Nhiet tr Nikel: Tam o nhiet tr Nikel trong khoang t 60oC200oC, o nhay cao hn so vi Pt.

Bieu thc quan he ien tr / nhiet o cua nhiet tr Nikel:

R(T)=Ro [1+AT+BT2], (T= oC) (1.31)

Trong o: A=5,49167 x10-3/oC

B = 6,666667 x10-6/oC2

He so nhiet: Khi cho nhiet o bien thien 1 lng T xung quanh T ,ta co quan he ien tr / nhiet

o co the bieu dien nh sau:

R(T+T)=R(T)(1+R x T ) (1.32)

Vi R la he so nhiet nhiet o T, suy ra:

dT

dR

TRR

)(

1 (1.33)

T (1.29) va (1.30), he so nhiet ien tr Pt va Ni 0oC la:

Pt : R = 3,9 x 10-3/oC

Ni: R = 5,49 x 10-3/oC

Bu ien tr day dan:

Trong hau het cac trng hp, mach tao dong/ ap ra t cam bien nhiet ien tr kim loai thng la

mach cau. Khi at cam bien nhiet ien tr xa mach, can phai co day dan u dai. Luc nay ien tr cua

day dan Rf se tham gia vao thanh phan cua nhanh mach lam cau lenh can bang,va khi nhiet o thay oi

ien tr cua day dan Rf cung thay oi 1 lng Rf co the so sanh vi lng bien thien RT cua cam bien,

gay ra sai so.

Xet mach cau wheastone nh hnh 1.18:

Cho R1=R3= R4=Ro R2 = R3= Ro+RT

Vi Ro: ien tr tai 0oC

RT : ien tr tai ToC

Hnh 1.18: RT mac tren cau Wheastone

De dang tm c:

0

0

214

R

R

R

R

EV

T

Tsm

(1.35)

Thong thng: 2Ro RT

Suy ra:


04 R

REV Tsm

(1.36)

Trong mach bu day, cac day dan co ien tr Rf =Rfo + Rf co chieu dai bang nhau va c at

tham gia nh mot ien tr trong cac nhanh cua cau.

1- Mach bu day 3 day:

Hnh 1.19: a) Mach bu 3 day day th 3 noi nguon

b) Mach bu 3 day day th 3 noi ngo ra

Trong mach bu 3 day hnh 1.19a, day th 3 Rf Rs noi tr nguon nen se khong anh hng.

Ta co: R1=Ro , R3=Ro ,

R2 = RC + Rfo ,R4 = Ro + Rfo , (1.37)

Chon R1, R2, R3, R4 thoa ieu kien cau can bang.

Mach bu 3 day co day th 3 noi vi ngo ra hnh 1.19b co Rf tong tr ngo vao tang sau tai 2

iem AB nen Rf khong anh hng .

Ta co: R1=Ro + Rfo , R3=Ro

R2 = RC + Rfo , R4 = Ro (1.38)


2- Mach bu day 02 day :

Hnh 1.20 minh hoa mach bu day 02 day.

Ta co: R1=Ro , R3=Ro (1.39)

R2 = RC + 2Rfo , R4 = Ro + 2Rfo


Hnh 1.20: Mach bu day 2 day

3- Mach bu day 4 day:

Trong mach bu day 4 day hnh 1.21, ta se xac nh c gia tr cua RC theo ieu kien can bang

tuy thuoc vao v tr ket noi cac nhanh .

Cau can bang lan 1: ket noi A vi a, D vi f, F vi b ,chnh R1= R1 e cau can bang ta co:

(R1 +Rf1).Ro = (RC +Rf2).Ro (1.40)

Cau can bang lan 2: ket noi A vi f, D vi a, F vi e,chnh R1 = R1 e cau can bang ta co:


(R1+ Rf2).Ro = (Rc+Rf1).Ro (1.41)

T (1.40) va (1.41) suy ra :

2

"' 11 RRRc

(1.42)

Hnh 1.21: Mach bu day 4 day

e tranh anh hng nhiet gay ra bi dong qua nhiet tr kim loai, ngi ta thng phan cc dong

be, thong thng


Nguyen tac chung e tuyen tnh hoa la mac them mot ien tr Rl, goi la ien tr tuyen tnh hoa

song song hoac noi tiep vi cam bien. Chon Ti la iem tuyen tnh sao cho trong tam o a xac nh t

T1 en T2, ac tnh at c la tuyen tnh nhat. Thong thng iem chon Ti la iem uon cua ac tuyen

ban au. Goi Vm la ien ap ngo ra mach chuyen oi sang ien ap, yeu cau tuyen tnh thoa ieu kien:

02

2

iTT

m

dT

Vd (1.45)

T (1.45) ta xac nh c gia tr Rl.

1- ien tr Rl mac song song:

Ta co: )(

)()(

1

1

TRR

TRRTR

c

c

Hnh 1.23: Tuyen tnh hoa ien tr Ni 50 25oC

Cho: 0)(

2

2

iTTdT

TRd

Suy ra: )()("

)('22

ic

ic

icl TR

TR

TRR (1.46)

Vi (dRc/dT)=Rc va (d2Rc/dT

2)=Rc

Trng hp nhiet tr kim loai:

Rc(T) = Rco (1+AT+BT2)

)()2( 2

ici

col TRB

BTARR

(1.47)

Trng hp Thermistor:

0

11exp)(

TTBRTR coc

i

iicl

TB

TBTRR

2

2)(

(1.48)

Xet ac tuyen nh hnh 1.24:

T1 : )(

)()(

11

111

TRR

TRRTR

c

c

(1.49)


Hnh 1.24: Nguyen tac tuyen tnh hoa 3 iem nhiet o.

T2: )(

)()(

21

212

TRR

TRRTR

c

c

(1.50)

Chon TM=(T1+T2)/2

2

)()(

)(

)()( 21

1

1 TRTR

TRR

TRRTR

Mc

McM

(1.51)

Suy ra:

)(2)()(

)()(2)()()(

21

2121

Mccc

ccccMcl

TRTRTR

TRTRTRTRTRR

(1.52)

2- Tuyen tnh hoa bang Rl mac noi tiep:

Ta co: sc

cm E

TRR

TRV

)(

)(

1

02

2

iTT

m

dT

Vd

)()("

)('22

ic

ic

icl TR

TR

TRR (1.53)

Hnh 1.27 Rl mac noi tiep

Mot phng phap tuyen tnh hoa bang cach mac ien tr noi tiep co the ap dung cho nhiet tr

kim loai nh sau:

Cam bien o nhiet co bieu thc:

Rc(T) = Rco(1+AcT+BcT2)

Cam bien tuyen tnh hoa co bieu thc:

Rs(T) = Rso(1+AsT+BsT2)

ien tr tong:

R(T) = Rco+Rso+(RcoAC +RsoAS)T+(RcoBc+ RsoBs)T2 (1.54)

R(T) tuyen tnh thoa ieu kien:

RcoBc = - RsoBs

Thong thng ngi ta s dung Pt mac noi tiep vi Ni e tuyen tnh hoa.


1.3.3: Cam bien nhiet diode va transistor:

Diode hoac BJT noi Bva C lam viec nh diode, khi phan cc thuan co mot dong ien co nh I,

ien ap phan cc thuan v tren diode la ham thay oi theo nhiet o.

Hnh 1.26 : Cam bien nhiet tiep xuc P- N

a) Diode b) BJT mac noi tiep nh diode c) Cap BJT vi sai mac nh diode

Bieu thc dong ien thuan qua diode:

1exp0

KT

qvII (1.55)

Do I>>I0 nen:

KT

qvII exp0 (1.56)

Trong o:

KT

qvCTI m exp0 (1.57)

la dong ien ngc

v = 1,12 V oi vi Si

m=3

C hang so phu thuoc vao hnh dang tiep xuc

q= 1,6x10-19C

k hang so Boltzman

T: oK

Bieu dien sang ien ap:

LogCq

KTmLogT

q

KTLogI

q

KTvv (1.58)

Hang so C va I co the loai tr neu ta biet c ien ap v1 tai nhiet o T1 t o:

111

1 1T

TLog

q

KTm

T

Tv

T

Tvv

(1.59)

T (1.59),ta xac nh o nhay ve nhiet:

11

1 11

)(T

TLog

q

KTm

Tvv

dT

dv (1.60)

Viet di dang ham theo v:

T

vvq

Km

dT

dv 1)( (1.61)


Trong vung nhiet o lam viec cua ban dan 50oC +150oC co the bo qua so hang th 2 , ta tnh

c:

CmVdT

dv /2 (1.62)

e loai tr anh hng theo nhiet o cua dong nghch Io , ta mac mach nh hnh 1.26c ta co:

0

11

101 exp

I

ILog

q

KTv

KT

qvII

0

22

202 exp

I

ILog

q

KTv

KT

qvII

ien ap vi sai ngo ra:

Lognq

KT

I

ILog

q

KTvvvd

2

121 (1.63)

Vi n he so nhan cac nguon dong

Thay cac gia tr vao:

):,:(;56,86 KTVvTLognv dd (1.64)

Gia s chon n=2 vd= 59,73 T.

ien ap vi sai ra tuyen tnh vi nhiet o

Cac cam bien nhiet s dung vi mach:

1- Vi mach cam bien nhiet nguon dong AD590:

Vi mach AD590 la nguon dong cam bien nhiet, tuyen tnh. Mach nguyen ly n gian A090

nh hnh 1.27a.

Dong qua nhanh Q3Q2 va Q4Q1 la IT/2, ien ap BE Q1:

0

12I

ILog

q

KTV TBE

Hnh 1.27: a) Mach nguyen ly AD590

b) ng dung c ban nguon dong AD590

Tng t dong IT/2 qua Q3Q2 . Trong thc te Q2 la 8 transistor mac song song, cac BJT nay

giong loai Q1 nen dong qua moi BJT la IT/16. ien ap BE moi BJT:

0

216I

ILog

q

KTV TBE

T o ien ap vi sai ngo ra:

821 Logq

KTVV BEBE


Va: 2

21T

BEBE

RIVV

Suy ra: 82

Logq

KT

RIT

Neu chon: R= 358 :

KAT

IT /1 (1.65)

hnh 1.27b, dong IT c chuyen thanh ap:

Vd = IT x Ra hay Vd = T x Ra (T=oK, V = V, R= )

2- Vi mach cam bien nhiet tao ap LM 335:

Hnh 1.28: a) Mach nguyen ly LM335

b) Ky hieu va phan cc LM335

Vi mach LM335 la cam bien nhiet tuyen tnh lam viec nh mot diode zener.Mach nguyen ly

c ban vi mach LM335 nh hnh 1.28a,dong qua Q1 va Q10 bang nhau.Thc te Q10 gom 10 BJT mac

song song, cac BJT giong nh Q1. T o ien ap BE tren Q1va moi BJT trong Q10 la:

10Logq

KTVbe

TVVbe 200)(

ien Vbe ap tren R tao dong hang qua nhanh R2,R,R1; suy ra:

VT = (R1+R2+R) Vbe/R

Thay cac gia tr vao:

VT(mV) = 10T (T:oK) (1.66)

Bo khuech ai A on nh dong collector qua dong Q1 va Q10 thong qua hoi tiep t ap cc B.

Tham kho vi mch DS1822 cm bin nhit ng ra tn hiu s.

1.3.4: Cap nhiet ien( Thermocouple):

Cap nhiet ien gom 2 kim loai dan ien A va B tiep xuc hai au, moi au tiep xuc at 2

nhiet o khac nhau T1 va T2 se sinh ra mot sc ien ong EABT2T1 phu thuoc vao tnh chat 2 vat dan AB

va nhiet o hai au tiep xuc. Thong thng 1 au tiep xuc c gi nhiet o co nh T1= Tref goi la

au nguoi; mot au tiep xuc at trong moi trng can xac nh nhiet o T2= TC . Sc ien ong sinh ra

se ty le vi nhiet o TC.

Cap nhiet ien thng c ng dung trong cac trng hp:

- o tam nhiet o cao (en 1800oC).

- Moi trng o cong nghiep, nhieu chan ong bui bam, noi chung can loai cam bien co cau tao

ben chac.

- Khong b anh hng dong nhiet do dong phan cc.


Hnh 1.29: Cau tao c ban cap nhiet ien

Cac loai cap nhiet ien:

Loai E: Chromel/ Constantan

Loai J: Fer/Constantan

Loai T: ong /Constantan

Loai K: Chromel/Al

Loai R: Platin Rhodium (13%)/ Platin

Loai S: Platin Rhodium (10%)/ Platin

Loai B: Platin Rhodium (30%)/Platin Rhodium (6%)

Noi chung ac tnh sc ien ong theo nhiet o cua cac loai cap nhiet ien eu phi tuyen .

Hnh 1.30 minh hoa ac tuyen cac loai cap nhiet ien.

Hnh 1.30: Bien thien sc ien ong cac loai cap nhiet ien.

e xac nh quan he sc ien ong/ nhiet o ta co 2 cach:

+ Cach 1: tra bang so lieu sc ien ong /to

+ Cach 2: bieu dien quan he sc ien ong/ to theo a thc dang:

ii

iiTaE

8

0

(E:V,T:0C) (1.67)

Ga tr ai c xac nh thong qua bang tra.

Cac hieu ng nhiet ien:


1. Hieu ng Peltier:

Xem hnh 1.31a, tai v tr tiep xuc cua hai kim loai khac nhau A va B at trong vung nhiet o T,

se phat ra mot hieu ien the goi la sc ien ong Peltier

VM-VN=PT

A/B (1.68)

o nh luat mach kn:Trong mot mach kn gom cac kim loai khac nhau tiep xuc tao ra, tong

cac sc ien ong Peltier bang 0.

o Tren hnh 1.31b ta co:

PTA/B +PT

B/C +PT

C/D + PT

D/A =0 (1.69)

Phng trnh tren co the viet lai:

PTA/B +PT

B/C +PT

C/D = - PT

D/A

Hay PTA/B +PT

B/C +PT

C/D = PT

A/D

PTA/D = - PT

D/A (1.70)

Hnh 1.31: Cac hieu ng nhiet ien

a) Hieu ng Peltier b) nh luat mach kn

c) Hieu ng Thomso d) Hieu ng Seebeck

2. Hieu ng Thomson:

Gia 2 iem M va N co nhiet o khac nhau trong 1 vat dan ong chat A , se phat ra mot sc

ien ong phu thuoc vao tnh chat vat dan va nhiet o TM, TN.

M

N

NM

T

T

A

TT

A dThE (1.70)

(1.70) goi la sc ien ong Thomson, hA la he so Thomson cua vat dan va la ham theo to.

- Neu tren toan bo vat dan ong chat co cung nhiet o th sc ien ong Thomson bang 0.

3. Hieu ng Seebeck:

Trong mach kn gom hai vat dan khac loai AB co 2 tiep xuc at 2 nhiet o khac nhau T1 va

T2, se tao thanh mot cap nhiet ien .

Cap nhiet ien nay tao ra 1 sc ien ong Seebeck 12TT

ABE bao gom ca sc ien ong Peltier va

Thomson.

Sc ien ong gia a va b:

2

1

T

T

Aab dThe


Sc ien ong gia b va c:

2/T

BAbc Pe

Sc ien ong gia c va d:

1

2

T

T

Bcd dThe

Sc ien ong gia d va a:

1/T

ABda Pe

Sc ien ong Seebeck c tnh nh sau:

2

1

1212 )(///

T

T

BAT

BAT

BATTBA dThhPPE (1.71)

Mach o ien ap sinh ra t therocouple:

Trong thc te, cap nhiet ien gom 2 day kim loai khac nhau, mot au han noi lai goi la au

nong va 1 au e h goi la au nguoi.

Tai au nguoi phai gi nhiet o Tref co nh.Ky hieu +/- bieu dien cc tnh sc ien ong sinh

ra khi au nong c at vao moi trng nhiet o TC .

Hnh 1.32: Cau tao thc te cap nhiet ien

S o mach o cap nhiet ien thng mac nh hnh 1.33:

Hnh 1.33 : Mach o cap nhiet ien

Cap nhiet ien AB co au nong at trong vung nhiet o Tc , au nguoi tai vung nhiet o Tref .

M1 va M2 la cac oan day dan noi vung nhiet o Tref en Ta1 va t Ta1 en Ta2 tai v tr mach o. M3 la

mach vao cua mach o.

Bieu thc sc ien ong e sinh ra nh sau:

c

ref

ref

ref

a

a

a

a

a

a

a

a

a

a

a

a

ref

ref

ref

c

c

T

T

A

T

AM

T

T

M

T

MM

T

T

M

T

MM

T

T

M

T

MM

T

T

M

T

MM

T

T

M

T

MB

T

T

BT

BA

dThPdThPdTh

PdThPdThPdThPdThPe

//

/////

1

1

1

1

12

1

2

2

2

23

3

2

3

2

32

2

1

2

1

21

1

11

n gian cac so hang ta c:

refcref

c

ref TT

BA

T

T

AB

T

BATc

BA EdThhPPe /// )( (1.72)


Hay noi cach khac, sc ien ong Seebeck sinh ra tren 2 iem cua au nguoi nhiet o Tref vi

au nong at trong vung nhiet o can o Tc.

e tuyen tnh hoa ac tuyen cap nhiet ien trong tng vung nhiet o, quan he sc ien ong

hay ien ap theo nhiet o c n gian thanh bieu thc sau:

)( refcsc TTE (T:0C) (1.73)

s: he so Seebeck phu thuoc vao tng vung nhiet o.

tam nhiet o thap (300oC) he so Seebeck cua cac loai Thermocouple c cho theo bang (1.1):

Bang 1.1: He so Seebeck cac loai cap nhiet ien(T


V du: Cap nhiet ien Pt- Ph (10%)/Pt co sc ien ong phat ra 2,80 mV ng vi au nguoi at

tai nhiet o Tref =26oC , t bang tra E26oC0=0,15 mV.

Do o ETc 0o=2,95 mV ng vi Tc = 368oC.

3- Tref thay oi nhiet o theo moi trng chung quanh:

Hnh 1.34: Mach bu au nguoi tao ra CT BAaaETV

0/)(

Khi nhiet o au nguoi Ta= Tref thay oi ta phai co mach bu au nguoi e am bao on nh

nhiet o au nguoi, cu the la tao mot nhiet o chuan Tref tai au nguoi xenm nh bang 0oC

Ta co: 0//0

/aacc T

BATTBA

TBA EEE

Trong o cap nhiet ien tao acTT BAE / ,con mach bu nhiet au nguoi tao ra ien ap CT

BAaaETV

0/)( .

Mach bu au nguoi co the s dung day bu nhiet hoac mach cam bien nhiet co he so nhiet gan

bang he so nhiet cua cap nhiet ien.

Hnh 1.35 minh hoa mach bu nhiet au nguoi s dung cam bien LM335.

Hnh 1.35: Mach bu to au nguoi s dung LM335

Ta co: 0//0

/21aaxx T

BATTBA

TBA EEEVV

a

ax

TTTBA V

RR

REV

21

2/1

Vi VTa = (273+Ta) x10-2 V la ien ap sinh ra tren cam bien LM335 at nhiet o Ta.

V2= K Eref ien ap chnh 0 tao 0V ngo ra khi Tx=0oC

Ta c : refaT

BA KETRR

RE a

2

21

20/ 10).273(

Khi Ta=0oC: 00/

aTBAE

Suy ra: 010.273 2

21

2

refKE

RR

R (1.75)


T o : 2

21

20/ 10.

aT

BA TRR

RE a (V) (1.76)

Chon: sRR

R

2

21

2 10.

He so Seebeek cua cap nhiet ien se bu c nhiet o au nguoi, bieu thc cuoi cung co dang:

xsasaxs TTTTVV )(21 (1.77)

Tham kho vi mch AD594/595 o nhit dng thermocoupe c mch b u ngui bn trong.

1.4: Cam bien v tr va o dch chuyen:

Cac cam bien v tr va o dch chuyen co the c phan thanh 2 loai: ng thang va goc quay.

Cam bien v tr va o dch chuyen ng thang co n v o la chieu dai (m hoac mm), cam bien v tr

va o dch chuyen goc quay co n v o la rad hoac o, mot rad bang 180/ o (57,3o). Hnh 1.36

minh hoa cac phng thc o ng thang va goc quay.

Hnh1.36 : a)- o ng thang b) o goc quay

c) - Chuyen t goc quay sang ng thang

1.4.1: Cam bien ien tr / phan ap:

Hnh 1.37: Cam bien ien tr a)- Loai tuyen tnh b)- Loai goc quay

Vi bien tr tuyen tnh: sout ELxE )./( (1.78)

Vi bien tr quay: sLout EE )./( (1.79)

Bien tr co dang day quan vi bc quan la N. o phan giai cam bien c tnh la s thay oi

ien ap khi con chay bien tr dch chuyen c mot bc quan.

ien ap moat bc quan: NEE sT /

o phan giai: NEES Ts /100)./100((%) (1.80)

Sai so gay ra khi mac tai RL:

Khi mac tai RL vao nh hnh 1.38, ta co RL mac song song vi phan ien tr aRp vao tao nen

mot ien tr song song )./()..( LpLp RRaRRa

Phan ien tr con lai cua Rp la (1-a)Rp


ien tr tng ng toan mach bay gi la:

Lp

Lp

peqRaR

RaRRaR

)1( (1.81)

Hnh 1.38: Sai so gay ra khi mac tai RL ien ap ngo ra tng ng: LpLppLpLpout RaRRaRRaRaRRaRE /()()1(/)]/()[(

Hay: sout Earar

aE

21 (1.82)

Vi Lp RRr /

Trng hp h mach tai: Eout = aEs

Sai so sinh ra: eS = aEs - Eout

ss Earar

arae

2

2

1

)1(

(V) (1.83)

Sai so sinh ra tnh theo % theo ES:

2

2

1

)1(100(%)

arar

araes

(1.84)

1.4.2: Cam bien ien cam:

Bieu thc ien cam cuon day:

f

fll

SNL

0

20

1 (1.85)

o = 4.10-7

N: so vong day

S: tiet dien loi t

lf: chieu dai trung bnh ng sc trong mach t

l0: chieu dai trung bnh ng sc trong khong kh

f: o t tham cua loi vat lieu t (103104)

Hnh 1.39: Nguyen ly cam bien ien cam thay oi khe h t.

ien cam cua cuon day se thay oi theo o dch chuyen khe h t .


Thc te: lo lf/f nen (1.85) co the n gian thanh:

0

20

l

SNL

(1.86)

Mot s bien thien x cua loi dan en khe h t thay oi lo =2x va iem cam mi se hnh

thanh:

0

0

20

21

1

l

xl

SNLL

(1.87)

Vi:

0

20

20

21

2

l

xx

l

SNL

va

0

02

1

12

l

xl

x

L

L

Neu x lo co the bien oi thanh:

...

221

22

0020

20

l

x

l

xx

l

SNL

(1.88)

o nhay:

...

221

22

0020

20

l

x

l

xx

l

SN

x

LS

(1.89)

e tang o nhay va loai bo thanh phan bac 2 anh hng en o phi tuyen, ta s dung mach t

kep gom 2 cuon day giong nhau L va L nhng o lech chuyen loi ngc nhau nh hnh 1.40

Hnh 1.40: Mach t kep co o dch chuyen ngc nhau.

ien cam bien thien cua cuon L khi dch chuyen loi 1 oan x ve pha L

0

20

20

21

2'

l

xx

l

SNL

(1.90)

Vi x lo:

...

221

2'

2

0020

20

l

x

l

xx

l

SNL

(1.91)

ien cam bien thien tong cong cua mach:

...

21

4'

2

020

20

l

xx

l

SNLL

(1.92)

o nhay tang gap oi va loai c thanh phan bac 2.

1.4.3: Bien ap vi sai:

Cau tao bien ap vi sai gom mot cuon s cap va 2 cuon th cap giong nhau quan oi xng quanh

cuon s cap. Loi bien ap la mot truc vat lieu t co the dch chuyen thang hay quay nh hnh 1.41 a,b.


th cap ta ket noi ngc au 2 cuon th cap e ho cam sinh ra t 2 cuon th tac ong len cuon s cap

M(x)va M(x) ngc chieu nhau.

Khi dch chuyen truc , 2 ho cam M(x) va M(x) se thay oi theo o dch chuyen x.

Xem mach tng ng hnh 1.41c , cho e1= E1cost:

Hnh 1.41: a) Nguyen ly bien ap vi sai dch chuyen thang

b) Nguyen ly bien ap vi sai dch chuyen quay

c) - Mach tng ng

)94.1(]))(")('([)]([)(

)](')("[

0)](")('[)]"'("'[

)](")('[)(

221

2211221

1

122222

21111

xMxMLLRRLRLjRRR

exMxMRjV

ixMxMjiLLjRRR

ixMxMjiLjRe

ii

im

i

(1.93)

Vi L2 =L2 +L2 , R2 =R2 +R2

Mach tng ng tren bo qua anh hng cua cac tu ky sinh.

Tai goc toa o O, x=0 M(0) = M(0).

Cho Ri rat ln (Ri>50K)co the tnh gan ung Vm:

11

1)](')("[

LjR

exMxMjVm

(1.95)

Lu y: M(x) va M(x) bien thien ngc nhau xung quanh x=0, neu ta co:

M(x)= M(0)+ax+bx2 .

M(x)=M(0)-ax+bx2 ..

Suy ra: M(x) M(x) =-2ax

Va xLjR

aejVm

11

12

(1.96)

Vm ty le tuyen tnh vi o dch chuyen x.

1.4.4: Cam bien ien dung:

1- ien dung thay oi be mat:

Trng hp ien dung n:

C (x)= k(x) (1.97)

Dang xoay: D

rK

360

20 (x=0) (1.98)

r: ban knh ban cc.

D: khoang cach gia 2 ban cc.


Dang tru: )/(

2

12

0

rrLogK

(x=l(m)) (1.99)

o nhay tnh theo C:

SC = K la hang so (1.100)

Hnh 1.42: a) - ien dung xoay n

b) - ien dung xoay oi

c) - ien dung dch chuyen ong tru n

d) - ien dung dch chuyen ong tru oi

o nhay tnh theo tong tr:

2

1

xKdx

dzSz

(1.101)

b phi tuyen

e tranh phi tuyen khi xet theo tong tr, ta dung phng an tu kep nh hnh 1.42 b,d.

Trng hp ien dung oi:

Goi x la o dch chuyen cc ai; C21 va C31 lan lt la ien dung cua cac tu thanh phan. Khi ban

cc dch chuyen mot khoang x:

)/1()/1()(

)/1()/1()(

031

021

XxCXxKXxXKC

XxCXxKXxXKC

(1.102)

Vi: Co = KX

X=L/2, L khoang dch chuyen cc ai vi tu hnh tru hnh (1.42d)

X= M/2 ,M khoang goc quay cc ai vi tu hnh quat hnh(1.42b)

Tnh theo tong tr:

X

x

CC

C

ZZ

Z

X

x

CC

C

ZZ

Z

12

1

12

1

3121

31

3121

21

3121

21

3121

31

(1.103)

Phan ap tong tr thay oi tuyen tnh theo o dch chuyen.

2- ien dung thay oi theo khoang cach 2 ban cc:

Theo hnh 1.43a, ien dung tnh c:

)/()( 00 dDAdC (1.104)

A: tiet dien ban cc

200 )/(/ dDAdddCSC (1.105)

ASz 0/1 (1.106)


o nhay theo tong tr la hang so.

Hnh 1.45: a) - ien dung n thay oi khoang cach gia 2 ban cc

b)- ien dung kep vi sai thay oi khoang cach gia hai ban cc

Xet hnh 1.43b vi tu kep vi sai;

0

0

000

31

0

0

000

21

/1

1

/1

1

/1

1

/1

1

DdC

DdD

A

dD

AC

DdC

DdD

A

dD

AC

(1.107)

Vi 000 / DAC

03121

31

3121

21

03121

21

3121

31

12

1

12

1

D

d

CC

C

ZZ

Z

D

d

CC

C

ZZ

Z

(1.108)

Phan ap tong tr ty le tuyen tnh vi o dch chuyen d

1.4.5: Bo ma hoa quang hoc ( optical encoder):

Cau tao bo ma hoa quang hoc gom 4 phan chnh :

1 nguon phat quang, mot a ma hoa , mot bo thu quang

va mach tao tn hieu. Bo phat/thu quang thng s dung

hong ngoai. Bo ma hoa v tr co 2 loai: loai gia so va loai

tuyet oi.

Bo ma hoa gia so tao cac dang chuoixung cac

ngo ra theo so day ranh tren a ma hoa. Hnh 1.44a minh

hoa a ma hoa tao 3 ngo ra xung A,B,Z.

Hai day ranh ngoai lech xen ke nhau e tao chuoi

xung A,B vuong pha nhau.Ranh trong cung ch co 01

lo/vong tao xung Z. Nh vay khi a quay 1 vong se co

NR so xung ra A,B va 1 xung ra Z. Hai ngo ra A,B nham

phan biet chieu quay.

o o dch chuyen goc: goi NR la tong so xung

ngo ra A,B khi a quay c 1 vong . NT la so xung em

c ngo ra khi a quay mot goc :

360R

T

N

N (1.109) Hnh 1.44: a) a ma hoa 3 day ranh tao 3 ngo ra xung A,B,Z

b) Gian o xung 3 ngo ra A,B,Z


Hnh 1.45: Bo ma hoa quang hoc o o dch chuyen thang.

o o dch chuyen thang: goi d la ng knh banh xe tiep xuc mat phang, chu vi cua banh xe la

d. Khi vat dch chuyen 1 oan x, bo ma hoa quay c 1 goc , tng ng iem tiep xuc dch

chuyen 1 oan x c tnh:

R

T

N

dNx

(1.110)

Bo ma hoa tuyet oi co a ma hoa c khac vach theo ma Gray hoac ma nh phan 8421.

Hnh 1.46: a ma hoa theo ma nh phan 8421

1.4.6 :Cong tac ra (proximity switch):

Cong tac ra la cam bien nhan dang s co mat cua oi tng ma khong phai cham vao oi tng.

Cong tac ra thng c s dung lam cam bien mach em , mach nhan dang phat hien .Co 3 loai cong

tac ra:cong tac ra ien cam, cong tac ra ien dung, cong tac ra quang.

Hnh 1.47: Cau tao c ban ra ien cam

Cong tac ra ien cam: cau tao can ban gom mach dao ong f cao kch vao cuon day loi ferrit ,

mach phat hien va on/off sw. Khi co dao ong a vao, xuat hien mot t trng xung quanh

cuon day (pha trc mat cam bien ). Khi cam bien gan vat lieu t tnh se lam t trng cuon day

thay oi dan en giam bien o dao ong, mach phat hien nhan dang s thay oi bien o dao

ong va tao tn hieu kch mach cong tac on/off lam viec.

o nhay cam bien c anh gia qua thong so khoang cach xa nhat t be mat cam bien

ma vat the con c phat hien.


- Cong tac ra ien dung: cau tao c ban cong tac ra ien dung nh hnh 1.48a, be mat co mot ong

dan ien hnh tru boc ben ngoai bang vo kim loai tao thanh 02 ban cc cua tu C1 co nh. Khi

at cam bien gan be mat vat kim loai, gia be mat cam bien va vat kim loai hnh thanh 1 tu

ien C(x). Ngoai ra con tu ky sinh sinh ra bi vo ngoai va vat kim loai Cp(x), ga tr (Cx) phu

thuoc vao lp ien moi gia be mat vat kim loai va be mat cua cam bien la chu yeu.

Mach phat hien co the s dung dao ong thay oi f hoac mach cau whenston,

Hnh 1.48: a) Cau tao c ban cong tac ra ien dung

b) Mach tng ng

Cong tac ra quang: s dung cam bien quang nh phan tren.

1.3 Cam bien bien dang:

Cam bien bien dang hien nay thng c s dung la loai cam bien ien tr sc cang (strain

gage) hay ien tr dan.Co 2 loai ien tr dan : ien tr dan kim loai va ien tr dan ban dan .

ien tr dan kim loai lam viec theo nguyen ly khi co ap lc tac ong hoac be mat ien tr b

bien dang ( theo be mat khao sat ma ien tr c dan len)lam cho chieu dai va ng knh day dan

thay oi , dan en gia tr ien tr thay oi theo. Con ien tr dan ban dan hoat ong theo dang ien tr

ap ien (piezoresistive), o linh ong cua hat dan thay oi theo ap lc tac ong, t o thay oi ien tr

suat cua ien tr dan ban dan.

Hnh 1.49: a) ien tr dan kim loai

b) ien tr dan ban dan

c) Dan ien tr len be mat khao sat

Vat lieu lam ien tr c gan tren mot e cach ien bang giay hay nha, dan len be mat can

khao sat bien dang (hnh 1.49c). o bien dang cua vat lieu se theo o bien dang cua be mat khao sat.

Ta co gia tr ien tr c tnh:

s

nlR (1.111)

: ien tr suat vat lieu

n : so bc quan day , n=1 vi ien tr dan ban dan

l: chieu dai thanh/ day ien tr tren mot bc quan

s : tiet dien thanh/ day

o bien dang gay ra thay oi ien tr:


ps

s

l

l

R

R

(1.112)

o bien dang theo chieu dai lam bien dang theo chieu ngang, canh a va b trong trng hp tiet

dien hnh ch nhat va ng knh d vi tiet dien hnh tron, o bien dang theo chieu ngang ty le vi o

bien dang theo chieu dai:

l

l

d

d

b

b

a

a

(1.113)

Vi la he so Poisson, chon bang 0,3 trong trng hp bien dang an hoi.

T (1.113) dan en bien dang theo tiet dien:

l

l

s

s

2 (1.114)

ien tr dan kim loai va ban dan khac nhau gia tr ien tr suat / .

Vi ien tr dan kim loai, bien thien ien tr suat theo the tch va hang so Bridgman:

V

VC

(1.115)

C: hang so Bridgman

Thay V=snl, l

l

V

V

)21( va

l

lC

)21(

Ta c:

)21()21(

)]21()21[(

CK

l

lK

l

lC

R

R

(1.116)

K: goi la he so dan (cang). Thay cac gia tr 3,0 va C1,he so K tnh ra xap x bang 2

Vi ien tr dan ban dan, bien thien ien tr suat phu thuoc vao ap lc va he so ien tr ap

ien :

l

l

(1.117)

Y: module Young

)21(

])21[(

K

l

lK

l

l

R

R

(1.118)

Hay K do 21

He so K thay oi t 100200 oi vi ien tr dan ban dan .

ien tr dan ban dan co o nhay cao hn ien tr dan kim loai rat nhieu, nhng o tuyen tnh

kem hn ien tr dan kim loai.

Cac loai ien tr dan kim loai va ban dan eu b anh hng bi nhiet o, nen thong thng

trong mach ien cam bien phai co phan t bu nhiet.

1- ien tr dan kim loai:

ien tr dan kim loai co thanh phan cau tao chnh la hp kim cua Nickel. Bang (1.3) mo ta cac

loai ien tr dan kim loai:

Bang 1.3: Cac ien tr dan kim loai

Hp kim Thanh phan He so dan

Constantan 45%Ni, 55% Cu 2,1

Isoelastic 50%Fe, 36%Ni, 8%Cr, 4%( Mn, Mo) 3,5


Karma 74%Ni, 20% Cr, 3% Cu, 3% Fe 2,1

Nichrome V 8% Ni, 20% Cr 2,5

Platin- Tungstene 92% Pt, 8%W 4,1

ien tr dan kim loai co 2 loai: day va ban mong.

Loai day co ng knh khoang 20m va e dan bang giay 0,1 mm hoac bang nha 0,03mm.

Loai ban mong tuy che tao phc tap hn nhng co u iem la tiep xuc be mat tot hn va giai nhiet

tot hn so vi loai day.

o nhay ien tr dan kim loai:

o nhay ien tr dan kim loai bao gom ca o nhay theo chieu doc l, va o nhay theo chieu

ngang lt.

Hnh 1.50: Bien dang theo chieu doc va ngang

ien tr cam bien: R= Rl+Rt

hay R

R

R

R

R

R tl

vi l

lK

R

R

l

l

va t

t

t

t

l

lK

R

R

o bien thien tng oi cua ien tr co the viet thanh:

t

t

tl

t

tl

l

l

l

RR

RK

l

l

RR

RK

R

R

Hay: t

ttl

l

lK

l

lK

R

R

(1.119)

tl

ll

RR

RK

: he so dan chieu doc

tl

tt

RR

RK

: he so dan chieu ngang

Thong thng vi day kim loai Kt 2x10-2K va Rt RL nen co the bo qua bien dang theo chieu ngang.

2- ien tr ban dan:

ien tr ban dan co 2 loai: Loai oan va loai

khuech tan:

Loai oan gom 1 oan hoac nhieu oan ghep Hnh 1.51: ien tr dan ban dan loai oan

vi nhau. Cac oan nay la cac thanh ban dan N hoac P.

Loai khuech tan: hoat ong bang cach khuech tan hat dan t lp e qua tiep xuc PN (hnh 1.52).

ien tr suat cua ien tr ban dan c tnh:

)(

1

pnq pn

(1.120)

q : ien tch n v

n va p lan lt la nong o ien t va lo trong t do

n, p o linh ong hat dan n,p.


Hnh 1.52: ien tr dan loai khuech tan

Trong ban dan loai N , nong o nguyen t cho la Nd:

dn

dNq

npNn

1

, (1.121a)

Trong ban dan loai P, nong o nguyen t nhan la Na:

ap

aNq

pnNp

1

, (1.121b)

o gia tr ien tr dan:

Phng phap thong dung e xac nh gia tr ien tr dan la s dung cau wheastone.

1- Cam bien tren mot nhanh cau:

Ta co: RC =RC0 +RC1

Rf = Rf0 +Rf Rf0

R0 = RC0+Rf0

00 /1

1

4 Cf

sm

RRl

lK

eV

(1.122)

Vi Rf0 RC0

l

lK

eV sm

4 (1.123)

Hnh 1.53: Cau wheastone 1 cam bien 3 day

2) Cam bien tren 2 nhanh cau bu nhiet:

Mot nhanh co ien tr dan chu ong o bien dang RC1= RC0+RC1, mot nhanh co mot ien tr

dan thu ong ch dung e bu nhiet , co gia tr ien tr thay oi theo to: RC2 = RC0+ RC2

0

)

4 C

mCsm

R

ReV

(1.124)

Vi 0)0 , CmCf RRR

Hnh 1.54: 2 nhanh cau wheastone la cam bien

3 Cau wheastone co 4 nhanh la cam bien:

Hai nhanh cau co bien thien ien tr dng: RC1= RC0+RC1)m va RC4=RC0+RC4)m

va hai nhanh cau co bien thien ien tr am : RC2 =RC0-RC2)m va RC3 = RC0 - RC3)m


0

)3)4)2)1

4 C

mCmCmCmCsm

R

RRRReV

(1.125)

Chon : RC1)m =RC4)m = RC)m

RC2)m = RC3)m = -RC)m

0

)

C

mC

smR

ReV

(1.126)

o nhay tang gap 4 lan, hn na con tuyen tnh hoa c ac tuyen.

Hnh 1.55: Cau wheaston co 4 nhanh cau la cam bien

1.6: Cam bien van toc:

Cac loai cam bien van toc thng s dung loai o van toc goc tnh bang rad/s hoac vong/phut.

Trong trng hp o van toc dai, ngi ta se chuyen sang o van toc goc. Co 3 loai cam bien o van

toc: may phat toc dc, may phat toc ac, may phat toc quang hoc.

1- May phat toc dc (dc tachometer): cau tao tng t nh may phat ien dc co choi than. Khi truc

rotor quay se phat sinh sc ien ong ngo ra:

60

2

30

LE

EE

RBNK

KSKE

(1.127)

Trong o:

E: Sc ien ong ngo ra (V) : van toc goc rad/s N: so thanh dan hieu dung

KE: hang so EMF, V/rpm R: ban knh trung bnh (m) L: chieu dai thanh dan (m)

S: van toc goc vong /phut B: cam ng t Wb/m2

2) May phat toc ac (ac tachometer): cau tao tng t nh may phat ac 3 pha, can phai co mach chnh

lu 3 pha ngo ra.May phat toc ac co the lam viec vi toc o cao,nhng ngo ra b phi tuyen khi toc o

thap (do ien ap m V tren diode chnh lu).Mot u iem na la may phat toc ac khong s dung choi

than.

3) May phat toc quang hoc: s dung bo ma hoa quang hoc (xem phan cam bien quang). o nhay rat

cao nen o toc o rat chnh xac.

Quan he gia toc o truc quay va so xung em:

cNT

CS

60 (1.127)

S: toc o truc quay vong/ phut

N: so xung phat ra/1 vong quay

C: tong so xung em c trong thi gian Tc

Tc : Thi gian em(s)


1.7: Cam bien lc:

Nguyen ly o cam bien lc theo nh luat II Newton:

f= Ma (1.128)

M : Khoi lng vat (Kg)

a: gia toc (m/s2)

Trong thc te xac nh gia toc vat rat kho, nen ngi ta s dung ieu kien can bang e loai tr

gia toc. Hai lc cung o ln nhng trai chieu tac ong len mot vat se lam vat can bang va gia toc bang

0. Tat ca cac phng phap o lc hau nh ap dung phng phap o lc can bang. Hai phng phap tao

ra lc can bang la:can bang 0 va dch chuyen.

Phng phap can bang 0 tng t nh can bang on tay , con phng phap dch chuyen tng t

nh can lo xo.

1.7.1: S dung cam bien lc ien tr dan (strain gage):

Ta a biet phan tren, khi tac ong mot lc len ien tr dan , se gay nen s thay oi chieu dai/

ng knh oi vi ien tr dan kim loai va hieu ng ien tr ap ien oi vi ien tr dan ban dan , gia

tr ien tr se thay oi.

Goi G la he so cang ( khi co tac ong lc ien tr se nen / gian).

ll

RRG

/

/

(1.130)

Ap lc S c nh ngha la lc tac ong tren tren mot n v dien tch (N/m2)

Trong cac vat lieu an hoi, ty so ap lc tren sc cang goi la module an hoi

SE (1.131)

E: module an hoi (N/m2)

S : ap lc (N/m2)

: sc cang phu thuoc vat lieu

Hnh 1.56 minh hoa ng dung ien tr sc cang o lc tac ong len dam.

Hnh 1.56: o lc tac ong len dam

Ta co: 2

6

bh

fLS (1.132)

S: ap lc (N/m2)

f : lc tac ong (N)

L: khoang cach t iem o en iem tac ong (m)

b: chieu rong dam(m)

h: be day dam (m)

Thay cac bieu thc tren: fEbh

GL

R

R2

6

(1.133)


Trong thc te cac ien tr sc cang o lc c ket noi thanh mach cau wheastone a co bu

nhiet, bu phi tuyen va co o nhay cao. Cac cam bien nay goi la loadcell thng s dung e o lc hoac

trong lng.

1.7.2: S dung bo phat lc kh nen:

Hnh 1.59: Bo phat lc kh nen

Hnh 1.59 minh hoa cau truc cua bo phat lc kh nen. Lc phat ong c can bang vi lc tao ra

bi ap suat khong kh tac ong len dien tch hieu dung cua mang chan.Vien bi va voi c sap xep sao

cho viec can bang cua hai lc la t ong. Gia s lc tac ong vao tang , thanh dan lc chuyen ong len

tren giam khe h m tiep xuc khong kh ben ngoai tao bi vien bi va voi. Ap suat trong buong tang len

va tai lap ieu kien can bang. Ap suat trong buong c xac nh nh sau:

Apf )3( (1.134)

f : lc tac ong (pound)

p: ap suat (pound/in.2)

A: dien tch hieu dung cua mang (in.2)

Ch can o ap suat ngo ra se xac nh c lc tac ong.

1.8: Cam bien ap suat:

Ap suat c nh ngha la lc tac ong len mot n v dien tch be mat chat long hoac kh.

Tam o va ieu khien ap suat trong cong nghiep rat rong t 0,1 Pa(0,001mmHg) en tren 100 MPa

(10,000 psi). cac phan t s cap cua cam bien ap suat thng chuyen oi ap suat sang o dch chuyen

hoac lc ,sau o cac phan t th cap(mach ien) chuyen o dch chuyen hoac lc sang dong ien, ien

ap hoac ien tn hieu kh nen tng ng.

Viec o ap suat luon luon theo ap suat tham chieu nao o.Thong thng ngi ta thng chon ap

suat tham chieu la ap suat khong kh. Ap suat o c chenh lech vi ap suat khong kh goi la ap suat

iem ta. Thi tiet va o cao se lam thay oi ap suat khong kh. Gia tr chuan ap suat khong kh la

101,3KPa hay 14.7 psi (760mmHg). Ap suat be hn ap suat khong kh la ap suat chan khong. Ap suat

bang 0 goi la chan khong tuyet oi. Chenh lech ap suat o so vi chan khong tuyet oi goi la ap suat

tuyet oi. Co the s dung mot ap suat bat ky lam ap suat tham chieu. Chenh lech gia ap suat o vi ap

suat bat ky lam tham chieu goi la ap suat vi sai.

1.8.1: Cam bien ap suat ien tr sc cang :

Di tac ong cua ap suat, qua he truyen c gom mang va thanh dan lc, lam nen/cang cac ien

tr day sc cang, dan en thay oi cac gia tr ien tr.R1, R2, R3, R4 mac thanh cau wheastone nen tao

ien ap ra ty le tuyen tnh vi ap suat.

Cam bien ap suat ien tr sc cang c s dung o tam ap suat cao t 10010.000 psi.

1.8.2: Cam bien ap suat loai lech hng:

Gom 2 phan: phan s cap chuyen oi ap suat o thanh o dch chuyen , phan th cap chuyen o

dch chuyen thanh bien thien cac phan t ien.


a) Cha co ap suat tac ong b) Ap suat tac ong

Hnh 1.58: S dung ien tr sc cang lam cam bien ap suat

Hnh 1.59a minh hoa phan t s cap la mot ong phang dang vong goi la ong Bourdon.Ong co

khuynh hng thang ra khi co ap suat tac ong vao,tao ra o dch chuyen t le vi ap suat.Loai ong

Bourdon co kha nang o t 010.000 psi.

Phan t ong nhun la mot hnh tru bang kim loai mong , than xung quanh co dang nhun. Hnh

dang nay cho phep no keo gian ra khi ap suat ben trong tang e can bang vi lo xo lam chuan. o dch

chuyen cua ong nhun ty le vi ap suat o c. Phan t ong nhun c s dung o ap suat en 100 psi,

va co the dung o ap suat chan khong va ap suat tuyet oi.

Phan t mang co the phang hoac nhun. Khi ap suat tac ong len mang, mang se dch chuyen mot

oan can bang vi lo xo lam chuan hoac cam bien lc.

Hnh 1.59: a) Phan t s cap dang ong Bourdon

b) Phan t s cap dang ong nhun

c) Phan t s cap dang mang

Hnh 1.60 minh hoa cac dang phan t th cap.

Trong hnh 1.60a, o dch chuyen lam di chuyen con chay

cua bien tr tuyen tnh, dan en thay oi gia tr ien tr.

Trong hnh 1.60b, o dch chuyen lam di chuyen loi sat

cua cuon day, dan en ien cam cuon day thay oi.

Trong hnh 1.60c , o dch chuyen lam di chuyen mang

hay mot ban cc tu ien lam thay oi ien dung.

Hnh 1.60: a) Phan t th cap ien tr

b) Phan t th cap ien cam

c) Phan t th cap ien dung


1.9: o mc chat long:

Viec o mc chat long co the thc hien trc tiep bang cach theo doi be mat chat long, hoac gian

tiep bang cach o cac thong so lien quan en mc chat long. Phng phap trc tiep phai co gng va

phao va bo ch th ngoai, mac du n gian va tin cay, nhng kho tao tn hieu ieu khien. Ngc lai

phng phap gian tiep de dang tao tn hieu ieu khien.

Cac phng phap gian tiep o mc chat long co the ke ra nh sau:

Phng phap dung phao noi chuyen oi mc thanh o dch chuyen

Phng phap cam bien ap suat

Phng phap au do ien dung

1.9.1: Cam bien mc chat long dung phao:

Hnh 1.61 mo ta nguyen ly cam bien mc chat long dung phao. Khi mc chat long thay oi tao

o dch chuyen phao, thong qua c he banh xe va truc quay se quay bien tr tuyen tnh (hoac bo ma hoa

quang hoc).Gia tr ien tr se t le tuyen tnh vi mc chat long .

Phng phap nay co the o mc chat long vi o sau thoai mai, nhng se b sai so do ma sat

trt gia day va banh xe truc quay.

Hnh 1.61: Cam bien mc chat long dung phao tao o dch chuyen

Hnh 1.62 minh hoa cam bien mc chat long dung phao chuyen thanh o dch chuyen, thong qua

on tay va goi ta chuyen thanh lc tac ong len cam bien loadcell. Lc tac ong len loadcell se bang

hieu gia trong lc cua phao va lc noi(lc ay Archimede) cua chat long xung quanh phao.

gAhMgf (1.135)

f: lc tac ong len load cell

M: Trong lng phao

g = 9,81m/s2

: khoi lng rieng chat long (Kg/m3)

A: tiet dien ngang cua phao (m2)

h: chieu dai cua phan phao b ngap nc(m)

Hnh 1.62: Cam bien mc chat long dung phao/ o dch chuyen en lc


1.9.2: Cam bien mc o ap suat tnh:

Hnh 1.63 minh hoa phng phap cam bien mc bang cach o ap suat tai mot iem nao o trong

chat long thong qua o xac nh c mc chat long.

Hnh 1.63: Cam bien ap suat at gan ay cua bon cha e o mc

Ta co:

ghP (1.136)

P: ap suat tnh

: khoi lng rieng Kg/m3

H : chieu cao mc chat long tren iem o(m)

g= 9,81 m/s2

Lu y: Phng phap cam bien ap suat ch ap dung khi mat thoang tren h, neu mat thoang tren

ong kn phai s dung phng phap o ap suat vi sai.

1.9.3: Cam bien mc dung au o ien dung:

au o ien dung co lp cach ien ngoai la mot ban cc va bon cha la ban cc con lai. Mc

chat long thay oi se ty le bien thien ien dung.

Hnh 1.64 : Cam bien mc dung au do ien dung


Cm bin

Ngun DC

Cu WZero&calip

Ngun cung cp

K DC LPFOutput

Kch thch

Cm binKch thch

Cu W Zero&calip K AC

Tch sng

nhy pha LPF

Ngun

cung cp

To sng mang

Output

1.10: Chuyn i tn hiu cm bin (signal conditioning)

1.10.1: Gii thiu:

Mch chuyn i tn hiu cm bin c chc nng chuyn i p ng ng ra ca cm bin thnh i lng in di dng in p, dng in, rng xung, tn s, tn hiu s ph hp vi iu kin ng vo ca phn x l tip theo.

V d: ng ra ca thermocoupe CA(K) c p ng 41 V/ C . nhy in p ny qu b, ta

cn phi c mch khuych i DC nng nhy in p thermocoupe ln ln ti hng mV chng hn mi c th a vo b ADC chuyn sang tn hiu s.

Hoc ta s dng cu wheastone chuyn s bin i in tr ca cm bin loi in tr nh Pt, straingage thnh in p ng ra cu v dng khuch i vi sai hay khuch i dng c khuch i tn hiu p ln nhiu ln.

Cc loi cm bin th ng cn cp ngun kch thch mi to tn hiu ra.Ngun kch thch c th l DC hoc AC.

Hnh 1.65 minh ha h thng chuyn i tn hiu cm bin DC c bn

Hnh 1.65: H thng chuyn i tn hiu cm bin DC

Cm bin l mt phn nhnh ca cu W.Ngun cp cu W l ngun DC. Tn hiu ng ra cu W c chun ha zero v calip trc khi a vo khuch i DC tng bin in p v b lc thng thp LPF loi b nhiu cao tn.

Nhng im thun li ca h thng chuyn i tn hiu cm bin DC:

1- Ng vo c th s dng khuch i vi sai c CMRR cao

2- tin cy v n nh nhit cao

3- D chun ha v tuyn tnh ha f thp

4- Kh nng chu iu kin qu ti cao

Nhc im chnh ca h thng DC l tri in p(theo nhit hoc bt n ca ngun cung cp). khc phc nhc im ny, ngi ta thng s dng cc b khuch i DC c tri thp(low drift).

gii quyt vn tri trong h thng DC,ngi ta s dng h thng AC nh hnh 1.66.

Hnh 1.66: H thng chuyn i tn hiu cm bin AC


Tn hiu cm bin

S/H 1

S/H 2

S/H 3

S/H 4

B phn knh

Analog

B

iu khin

ADC

Digital output

Ngun kch thch cp cho cu W l tn hiu AC gi l sng mang tn s cao t 50kHz200kHz. Sng mang phi c tn s ln hn tn s tn hiu ng ra cm bin t nht 5 n 10 ln. Tn hiu chuyn i t cm bin s iu ch sng mang v cho tn hiu iu ch ng ra ca cu W, sau c khuch i AC v qua b tch sng nhy pha. Ng ra tch sng nhy pha l tn hiu DC a v n nh li b dao ng to sng mang.

Trong h thng AC, vn tri tn s v tn hiu sai khng quan trng. Vn quan trng nht l n nh tn s v bin dao ng to sng mang.Chc nng ca b tch sng nhy pha dng gii quyt vn ny v loi b sng mang phc hi li tn hiu ng ra cm bin c khuch i. B lc h thng LPF thng l b lc tch cc loi b cc thnh phn sng mang v hi ca n cng nh cc nhiu cao tn.

Trong cc ng dng, h thng DC thng c s dng cho cc cm bin dng in tr, trong khi h thng AC c th ng dng cho cc cm bin dng tr khng (L,C) v truyn i xa qua dy ni n b x l.

Tn hiu cm bin sau khi c x l analog c th c gi n b thu thp v chuyn i sang tn hiu s (Data Acquisition and Conversion System) nh hnh 1.67.

Hnh 1.67: B DACS (Data Acquisition and Conversion System)

Tn hiu cm bin qua cc b ly mu v gi Sample & Hold (S/H) ly mu bin thin tn hiu vo, qua b phn knh analog v a vo DAC cho ng ra tn hiu s tng ng. Hot ng ca khi c iu khin bi b iu khin c th l mch s , vi x l, PC

Cc mch chuyn i tn hiu cm bin ni chung c th l khuch i DC,khuch i AC, khuch i dng c (IA) chuyn i dng/p,khuch i phi tuyn, to hm, lc,to xung& tn s, ADC, DAC, chopper/modulator phn sau,ta s kho st chi tit mt s dng mch chuyn i tn hiu cm bin tiu biu.

1.10.2: OPAMP v cc mch khuch i(K)thng dng:

Phn ny ch tm tt ngn gn v cc thng s & cc c tnh ca OPAMP v cc dng mch khuch i thng dng. kho st thm chi tit hn, c th tham kho thm cc ti liu v OPAMP.

Khi s dng OPAMP trong K DC c bit cn lu cc thng s sau;

Lch in p ng vo (Input offset voltage): Vos (mV)

Lch dng ng vo (Input offset current):Ios (nA)

Dng phn cc ng vo (Input bias current) IB (nA)

Tri in p (Voltage Drift): TC Vos ( V/ C )


T s nn tn hiu ng pha (CMRR): dB

Ba thng s u ch c ngha mt nhit nht nh (nh sn xut thng cho 25 C ). Thng thng khi thit k mch phi c mch b offset v phn cc dng ng vo nh hnh 1.68. Thng s tri in p rt quan trng nht l p dng trong cc h thng o nhit hay mch in nm trong mi trng nhit thay i trn tm rng. Ni chung phi c mch b nhit hoc chn OPAMP c TC Vos b nh OPO7 chng hn (TC Vos = 1,3 V/ C ).

Thng s t s nn tn hiu ng pha CMRR th hin kh nng trit nhiu tn hiu ng pha ca OPAMP.

1. Chnh offset qua R5 b) Chnh offset qua bin tr ngoi c) B dng phn cc vo

ni vo chn b offset OPAMP

Hnh 1.68: Mch b offset v dng phn cc vo

OPAMP OPO7 l loi OPAMP c lch in p v tri in p cc thp rt thch hp trong cc ng dng KDC cn offset v tri p thp ng vo . OPO7 c cc thng s tiu biu nh sau (tham kho thm ti liu v OPO7):

Vos = 75 V (max)

Ios = 3.8nA (max)

IB = (4.0nA (max)

TC Vos = 1,3 V/ C

CMRR = 103 dB (min)

Khi s dng OPAMP trong K AC, ngoi cc thng s trn, ta phi quan tm thm nhng thng s lin quan n tc lm vic v p ng tn s ca OPAMP:

Tc p ng ng ra (slew rate): SR (V/ S)

Tch s li bng thng (Gain. Banwidth product) : GBW (MHz)

OPAMP OP37 c:

SR=17V/ s

GBW=63MHz

rt thch hp cho KAC tri lch p thp , nhiu thp, tc cao (xem thm ti liu OP37)

1) Khuch i o:

- Tn hiu ng ra o pha ng vo

- H s K Av = 1

2

R

R (1.137)

- Tng tr vo: iR = 1R (1.138)

Hnh 1.69: Khuch i o


2) Khuch i khng o:

- Tn hiu ng ra ng pha ng vo

- H s K: Av = 1+1

2

R

R (1.139)

- Tng tr vo: iR rd (1+ )v

vo

A

A (1.140)

rd: tng tr vo vi sai ca OPAMP

Avo: H s khuch i vng h OPAMP Hnh 1.70: Khuch i khng o

3) Khuch i theo in p

- Tn hiu ng ra ng pha ng vo

- H s K: Av = 1 (1.141)

- Tng tr vo: iR =

- Tng tr ra : 0oR

Hnh 1.71: Mch theo in p

4) Mch cng:

)(0 cC

Fb

b

Fa

a

F VR

RV

R

RV

R

RV (1.142)

Chn FR = aR = bR = CR

)(0 cba VVVV (1.143)

Hnh 1.72: Mch cng

5) Mch tr: (K vi sai)

ba VR

RV

RR

R

R

RV

1

2

43

4

1

20 ))(1(

(1.144)

Chn 1R = 2R = 3R = 4R

ba VVV 0 (1.145)

Hnh 1.73: Mch tr

V d: S dng mch tr lm K cu W vi cm bin in tr nh hnh 1.74.

Cm bin c biu thc: RRRc 0

Ta c:

0

02R

ERV (1.146)

Hnh 1.74: Mch K cu

1.10.3: Khuch i dng c: (Instrumentation Amplifier: IA)

* Cc u im ca K dng c (IA):

o iu chnh c h s K v h s K chnh xc tuyn tnh


o Ng vo vi sai vi CMRR cao

o H s K v h s nhit n nh

o Tri v lch ng vo thp

o Tng tr vo rt ln, tng tr ra rt b

Hnh 1.75 m t mch IA c bn.

Hnh 1.75 khuch i dng c (IA)

21

21

1

21 iiA vR

Rv

R

RV

11

22

1

21 iiB vR

Rv

R

RV

12

1

20

21 iiAB vv

R

RVVV

(1.147)

Mt trong nhng ng dng rt thun li ca IA l s dng cu W nh hnh 1.76

Ta c cm bin in tr:

RRRc 0

RRER

Vab

022

1

0R

RVV Fab

1022 R

R

RR

ER F

(1.148)

Hnh 1.76: IA K cu W

Hnh 1.77 gii thiu mch IA AMPO1 ca hng ANALOG DEVICE

c tnh ca AMPO1:

o Lch in p 15 V

o Tri in p 0,1 CV o/

o Nhiu n 0,2 HzHzVpp 101,0

o Li ng ra mAV 50@10


o n nh ti dung n 1 F

o HSK 0,1-10.000

o Tuyn tnh 16bit Av=1000

o CMRR 140dB Av=1000

o Dng phn cc vo 1nA

o Bo v qu nhit ng ra

Xem thm chi tit trong ti liu AMP01.

Hnh 1.77: Mch IA AMP01

1.10.4: Khuch i cch ly (Isolation amplifiers)

B khuch i cch ly c s dng trong cc trng hp:

Cch ly cm bin v mch x l. V d: cm bin t trong mi trng nhit cao, c hi

ng truyn cm bin v mch in xa

Chng nhng nh hng nhiu v in p lm hng mch x l.

Gim nh hng nhiu do ng masse ni vng (ground loops).

Xem thm chi tit K cch ly AD202/AD204 (Analog device)

1.10.5: Chuyn i dng-p, p-dng:

1) - Chuyn i dng-p (I-V Converter):

p dng cho ng ra cm bin di dng dng in cn chuyn sang in p.

Ta c: RIV 0 (1.149)

Cc thng s lin quan 1

0rRr

arT

d

d

(1.150)

TRAv

/11

1

,

T

rRrR odi

1

//,

T

rR oo

1 (1.151)

1 : tham kho cc ti liu OPAMP Hnh 1.78: Mch chuyn I-V c bn

T : li vng

dr : tng tr vo vi sai

or : tng tr ra


Mch I-V nhy cao

pdng nh lut nt mch ti 1v :

02

1

1

11

R

vv

R

v

R

v o

Theo (1.149): iIRv .1

Thay vo ta c:

io KRIv (1.152a) Hnh 1.79: Mch I-V nhy cao

R

R

R

RK 2

1

21 (1.152b)

2)- Chuyn i p dng (V-I converter):

B V-I c p dng trong cc trng hp cn chuyn tn hiu p thnh dng in hoc to ngun dng cp cho cc cm bin cn kt ni qua ng dy di theo dng dng vng (current loop) m bo khng lm hng ngun cp khi c ngn mch xy ra.

V-I ti th ni:

hnh 1.80a: RiV oi

Suy ra: R

Vi io (1.153)

Lu ; dng oi ch ph thuc p ng vo iV v tr R , bt chp in p ti VL.

Ta c: Lio VVv

oHooL VVV

Trong : oLV l in p bo ha mc thp

oHV l in p bo ha mc cao

Nn: ioHLioL VVVVV (1.154)

Hnh 1.80: V-I ti th ni

V-I ti ni masse:

y l mch ngun dng Howland:


1R

vi io (1.155a)

Vi 1

2

3

4

R

R

R

R (1.155b)

satL VRR

RV

43

3

(1.155c)

Mt s mch to ngun dng :

Hnh 1.81: V-I ti ni masse

a) E

zE

R

VI b)

E

zE

R

VI

E

zEC

R

VIII 0 (1.156)

E

zEC

R

VIII 0 (1.157)

zDEELL VVVRIV 0 (1.156b) CEsatzEELL VVVRIV 0 (1.157b)

Hnh 1.82: Mt s mch to ngun dng n gin

*Tham kho thm v ngun dng trn cc trang web : - http : //www. aldinc.com/sc_current source.htm

- http : //www. 4qdtec.com/csm.html 1.10.6: Cc mch phi tuyn :

Mt s mch phi tuyn c s dng trong chuyn i tn hiu cm bin nh mch so snh, chnh lu chnh xc, Analog switch, ly mu & gi (S/H)

1. Mch so snh : S dng OPAMP K vng h lm mch so snh . Vng K: iV trong khong sV rt b

( hng V-mV) xem nh = 0) Do : 0 iV : osVV0 + CCV

0 iV : osVV0 - CCV Vi=Vi+-Vi

-

+ OSV : in p bo ha dng

- OSV : in p bo ha m

Hnh 1.83 : OPAMP v c tnh vng h


0Vi

V0

b) c tuyn hnh a

0 Vi

V0

d) c tuyn hnh c

Cc mch so snh tiu biu nh hnh 1.84.

Hnh 1.84 : Cc dng mch so snh c bn .

Ngun chun refV thng s dng diode Zener, c th kt hp bin tr iu chnh

hoc thm OPAMP mc theo in p c tng tr ra 0 v n nh .

Hnh 1.85 : To ngun refV n gin

Mt nhc im c bn nht ca mch so snh l rt d nhy nhiu v tri theo ngun, nhit ,... Ch cn ng vo bin thin rt b vi n vi chc V ng ra tc ng . khc phc, ta dng mch so snh c tr hay Schmitt trigger .

Hnh 1.86 : Cc dng mch Schmitt trigger c bn

Trong hnh 1.86a : OSTH VRR

RV

21

1

, OSTL V

RR

RV

21

1

(1.158)

Trong hnh 1.86b : OSTH VR

RV

2

1 , OSTL VR

RV

2

1 (1.159)

* Tham kho chi tit IC LM311 : OPAMP so snh tiu biu . 2. Mch chnh lu chnh xc :

Mch chnh lu bn sng ( haft wave rectifier : HWR) + Khi iV dng, OAV tng vt dng ln lm D on to hi tip nh mch theo in

p lm : io VV (1.160a)


+ Khi iV m, OAV m theo lm D off h mch D lm:

0oV , OSOA VV (1.160b)

Nhc im ca mch l khi iV chuyn t m sang dng,

OAV s tng t - OSV n iV + DonV .iu ny c th lm

mo tn hiu ra nu iV bin thin nhanh . ci thin, ta

thm diode kp 2D nh hnh 1.88 . Hnh 1.87: Mch HWR

+ Khi iV dng, 1D on, 2D off, mch tr thnh K khng o c:

io VR

RV

1

21 (1.161a)

+ Khi iV m,D1 off,D2 on:

onDOA VV 2 (1.161b)

Hnh 1.88 : Mch HWR ci thin

Mch chnh lu ton sng (Full wave Rectifier : FWR) Vi cch chn in tr nh hnh 1.89, ta c :

onDoffDVi 21 ,:0 :

io VR

RV

1

21

13

5

4

5Oio V

R

RV

R

RV

iVRR

RR

R

R

31

52

4

5 (1.162a)

iAV (1.162b) Hnh 1.89 : Mch FWR

offDonDVi 21 ,:0 :

ii AVVR

RV

4

50 (1.162c)

Trong c 2 bn k : iVAV 0 (1.162d) * Nhc im ca mch FWR hnh 1.89 l phi chn t l in tr tht chnh xc !

Hnh 1.90 l mch FWR ch cn s dng 2 loi tr ng t l v cho iVAV 0

(Phn ny chng minh qua bi tp )

Hnh 1.90 : Mch FWR dng 2 loi tr t l


VGS

+

-

VDS

+

-

0

ID

VDS

V 0GS=

VGSgim

0

ID

VDS

V 0GS=

1/rDS ON

a) JFET knh n

VGS


Vi V0

S/H

H S H S H S H S H S

t

t

0

0

+ Khi ,Q m:5 21 satonlQVVC 1D c phn cc ngun - VVEE 15 nn dn lm

GSOFFGS VV lm J1 off.

* iu kin gi tr Vimin duy tr 1J off:

GSOFFONDsatQEEi VVVVV 12min (1.164)

Analog SW MOSFET : Hot ng ca MOSFET tng t JFET ch analog SW Tham kho cc IC Analog SW CMOS nh CD4051,4052,4053 * Chn anlog SW : lu cc thng s

0ONR

OFFR

Tc p ng (ns) Mc in p iu khin

4. Ly mu & gi ( Sample & Hold : S/H): Mch ly mu v gi(S/H) ly mu tn hiu vo trong 1 thi on ngn v gi li tn hiu ly mu ng ra a vo x l tng k tip . Mch S/H thng c p dng trong cc h thng thu thp v bin i data , cc mch phn knh/ dn knh tn hiu analog .

Hnh 1.94 l mch ly mu & gi c bn .

211 ,, DDA lm vic nh mch theo in p ty theo

bn k tn hiu vo iV .Khi SW ng, 1D / 2D on v p ri

trn SW rt b nn p r trn tr 0, 1A s np nhanh p

trn HC v 0V s ly mu theo v tr tc thi .

Khi SW m, p trn C c gi theo iV cui thi im

ly mu v io VV .R dng np x HC qua oV m

bo p trn HC theo gi tr tc thi tn hiu vo iV .

* Yu cu : 1A : - Sai lch dng phn cc vo b

- Kh nng dng out put cao np HC nhanh Hnh 1.93 : Nguyn l S/H

- H s khuch i vng h VOA cao gim sai s do p ri trn SW v off set p ng

vo 2A

- C mch b tn s p ng nhanh

2A : - Dng phn cc vo thp trnh sai p trn HC

- p ng ng ra nhanh HC phi l t c mt mt in mi thp nh mylar

Hnh 1.94 : Mch S/H c bn


1.10.7: Cc mch to hm : 1. Mch tch phn :

a)- Mch tch phn b)- Mch tch phn thc t

Hnh 1.95 : Mch tch phn Theo hnh 1.95a, ta c :

dtVCR

Vt

i

F01

0

1 (1.165)

Chn 1RRc b dng phn cc vo .

tn s rt thp hoc DC,CF xem nh h mch dn n h s K ca mch gn bng h s K vng h ca OPAMP . khng ch h s K trong trng hp ny, ta thm

110RRF nh hnh 1.95b . Nh vy , h s K ti f thp hoc DC cn khong 10 ln .

2. Mch vi phn :

a)- Mch vi phn b) -Mch vi phn thc t Hnh 1.96 : Mch vi phn Theo hnh 1.96a, ta c :

dt

dVCRV iFo 1 (1.166)

f cao tr khng XC1 gim s lm tng k s K gy mt n nh mch . Mch vi phn thc t nh hnh 1.96b .

Chn 001.01.01 R FR gii hn h s K ca mch f cao

Tn s ct trn ca mch : 112

1

CRfb (ct trn -3dB) vi FFCRCR 11 (1.167)

Tn s ct di ca mch : 12

1

CRf

F

a , vi ab ff 20 (1.168)

3. Vi mch to hm ICL 8038 : * Tm tt 1 s c tnh ICL8038 : - To tn hiu ng ra ng thi sin, vung, tam gic - Tm tn s rng : 0,001 Hz - 300 KHz - mo thp 1% ( ng ra sin) - Tuyn tnh cao 0,1% ( ng ra tam gic) - Thay i chu k nhim v 2%-98%

Biu thc xc nh tn s ng ra :


vk

1/3Vcc

0 t

t0

0

0 T

vk

1/3Vcc

0 t

t0

2/3Vcc

T1 T2

V0Vcc

current output

Ref. current

Freq.out

GND

Vs

comp.input

threshold

R/C

1

2

3

4 5

6

7

8

LM311

RC

fo33.0

(1.169)

vi RRR BA

VR 100K dng iu chnh mo hi (THD%) ng ra sin t thp nht . * Xem chi tit ti liu IC L8038

1.10.8: B lc : Phn ny xin tham kho cc ti liu v mch lc s dng OPAMP- Lc s .

1.10.9 : Mch to xung, V/F & F/V: 1. Mch to xung :

Mch monastable : Hnh 1.97: Mch to hm ICL8038 Ta c : RCT 1.1 (1.170) o rng xung T, bit R hoc C s suy ra gi tr cn li. a)-Monostable b)- Gin xung

Hnh1.98 :Monostable s dng vi mch 555 Mch Astable

Ta c : 21 TTT

CRCRR 221 69.0)(69.0 (1.171)

o chu k T, bit 2R hoc C s suy ra gi tr cn li . a)- Mch Astable b)- Gin xung

Hnh 1.99: Mch Astable s dng IC 555

2. Mch V/F & F/V: Kho st vi mch LM331 chuyn i V/F v F/V tiu biu : * Tm tt 1 s thng s LM331 : - Tm tn s rng : 1Hz-100KHz - Tuyn tnh cao : 0,01% - Hot ng vi ngun n 5V - Ng ra tng hp theo mc logic yu cu (cc thu h) LM331 l vi mch chuyn i V/F & F/V thng dng Hnh 1.100: IC LM331 c s chn DIP8 nh hnh 1.100.


Hnh 1.101 : Mch V/F LM331 Hnh 1.101 minh ha mch chuyn i V/F tiu biu s dng IC LM331:

ttL

SIN

CRR

RVVf

1

09,2

)(0 (1.172)

Chnh VR 5K t t l 0f theo INV nh yu cu .

Khi cn chnh offset, thm ofof vR VR .

Hnh 1.102 l mch chuyn i F/V s dng IC LM331:

ttS

Lino CR

R

RfV 09,2 (1.173)

* Tham kho chi tit ti liu LM331 Hnh 1.102 : Mch F/V LM331

1.10.10 : B bin i ADC : 1. IC L 7109 :

ICL7109 l IC ADC 12 bit v bit du out put p dng nguyn l tch phn 2 dc .IC L7109 thch hp cho cc ADC p dng trong o nhit , p sut, trng lng,in tr, tc , dng, p (bin i chm). * Tm tt 1 s c tnh IC L7109 - Dng DIP 40pin - Ng ra 12 bit data v 1 bit du - Ouput 3 trng thi

- C tn hiu bt tay giao tip vi VXL


- CMRR cao : 90dB - Ng vo vi sai hoc common. - C ngun Vref out

- Data ng ra : ref

INout

V

VN 2048)( (1.174)

- Ng vo Vref in vi sai ty chn theo yu cu . * Xem chi tit ti liu IC L7109.

2. IC MX7705: MX7705 l IC ADC 16 bit, cng sut thp,2 knh,p dng nguyn l ADC Sigma-delta. MX7705 thch hp cho cc ADC trong o nhit ,p sut,trng lng,dng c o y khoa . * Tm tt 1 s c tnh MX7705 : - Dng DIP 16 pin - ADC Sigmal-delta 16 bit - Out put ni tip (SPI) - 02 ng vo analog v sai - B K on chip lp trnh c t 1-> 128 - CMRR cao n150dB (f=50Hz-60Hz) - Ngun cng sut thp : 1mW@ VVDD 3

- Mode 1 cc(1 du) : phn gii : 536.65

1

GAIN

VLSB REF (1.175)

- Mode 2 cc (2 du) : phn gii : 2536.65

1

GAIN

VLSB REF (1.176)

* Tham kho chi tit ti liu MX7705. 1.10.11 : B chopper/ Modulator : Trong cc trng hp ng ra cm bin l tn hiu in p b v bin thin chm, ng

truyn tn hiu t cm bin n mch x l xa, nu dng cc b K DC h s K cao s rt d b gy sai s do nhiu v tri. Mt phng php khuch i tn hiu DC b l dng b chopper (chp) hoc modulator(iu ch) chuyn tn hiu DC thnh tn hiu AC v s dng b K AC khuch i s loi c hin tng tri .

1. B chopper : Hnh 1.103 minh ha nguyn l lm vic b chopper . Ng vo Vi l tn hiu DC. Mt b iu khin SW lm SW chuyn v tr 1,2 tn s fc, do th cp bin p T s l tn hiu AC bin Vi(xung vung). B K AC khuch i tn hiu AC ny v to tn hiu ng ra Vo. B iu khin SW thng l mch to dao ng sng mang tn s fc c th t 50-400Hz. Hnh 1.103 : Nguyn l chopper

Hnh 1.104 : Mch chopper BJT

Trong hnh 1.104, khi sng mang ng vo cc B m lm BJT bo ha VVV CES 00 . Khi

sng mang ng vo cc B dng , BJT off, in p ng ra :


i

Li

C VRR

RV

0 iV ( LR iR ) (1.177)

Tn s sng ng ra bng tn s sng mang. 2. B Modulator:

Modulator dng nguyn l iu ch bin (AM) Tn hiu DC l tn hiu iu ch, tn hiu dao ng sin cao tn l sng mang . Hnh 1.105 minh ha b modulator s dng cu diode.Trong bn k u sng mang, im 1 dng, dng in chy t im 1 qua 1D , ngun tn hiu DC, Hnh 1.105: Modulator cu diode

3D v 1R v im 2 .Trong bn k sau, im 2 dng,

dng in chy t im 2 qua 1R , 2D , ngun tin hiu DC,

4D v im 1.Bin tc thi sng mang s c iu ch bi bin tn hiu DC .


Bi tp chng 1

1. Lit k cc cm bin dng nguyn l thay i in tr,biu thc quan h, nhy 2. Lit k cc cm bin dng nguyn l thay i in dung,biu thc quan h, nhy 3. Lit k cc cm bin dng nguyn l thay i in cm,biu thc quan h, nhy 4. Lit k cc cm bin cho in p/dng in ng ra, biu thc quan h, nhy . 5. Cu Wheastone thun tin cho kt ni cc loi cm bin no, vit biu thc quan h. 6. Cho quang tr PDV-9007(xem datasheet).

a) T c tuyn quang tr,vit li biu thc quan h: R=f(E);R: K,E:lux. b) Vit biu thc tnh nhy quang tr.Tnh nhy E=10 lux,E=100 lux. c) S dng phng php tuyn tnh ha mc Rl song song quang tr trong vng t E=10-

50 lux.Tm Rl. 7. S dng cc kt qu bi 6:

a) Thit k mt mch iu khin r le bng nh sng dng quang tr PDV-9007: Khi E=10 lux ,r le off. Khi E=50 lux,r le on.

b) Thit k mt mch o cng nh sng bng quang tr PDV-9007 tm E=10-50 lux. Mch cho in p ng ra t l tuyn tnh vi E.Vit biu thc in p ng ra.

8. Cho photo diode SD-076-14-21-011(xem data sheet). a) T c tuyn photo diode xc nh nhy photo diode trong vng nh sng

=600nm.T suy ra quan h Ip=f(),=10W-1mW trong vng nh sng =600nm. b) V mch o thng lng nh sng : mch in cho ng ra in p theo thng lng

nh sng .Vit biu thc in p ng ra. 9. Thit k mch o cng nh sng(E:lux)s dng IC SD-100-42-22-231(xem data sheet)

trong vng nh sng =600nm,tm o E=10 lux- 100 lux.Vit biu thc in p ng ra.

10. Cho Thermistor NTC KS102J2 c R( 1000)0T @ CT00 25 v ,360)( 1 TR 2@ CT

01 50

a) Tm h s B

b) V c tuyn ca thermistor R(T) vi T= 020 C- 040 C.

c) Tuyn tnh ha c tuyn trong tm T=200C-400C dng phng php mc lR song song

R(T), nh gi sai s . d) Lp li cu c vi lR ni tip R(T).

e) Lp li cu b vi tuyn tnh ha 3 im.

11. S dng thermistor cu 7 sau khi tuyn tnh ha T= CC 00 4020 kt hp vi mch

chuyn i tn hiu cm bin cho ng ra in p dc c nhy 10mV/ C0 . 12. V mch RTD Pt100 3 dy kt hp vi khuch i cu dng OPAMP to thnh mch cu

b 3 dy . Vit biu thc ng ra .

13. S dng ngun dng cp cho RTD Pt100 o tm 0-100 C0 .V s mch in chuyn

i thnh p ng ra TmVV ).(100 (T : C0 )

14. Thit k mch o nhit s dng Pt100 tm o 0-1000C.p ng ng ra l in p t l tuyn tnh tng ng t 1-5VDC.

15. Thit k mch o nhit s dng Pt100 tm o 0-1000C.p ng ng ra l ngun dng t l tuyn tnh tng ng t 4-20mADC.

16. V mch b nhit u ngui Thermocouple loi K(CA) s dng vi mch ngun dng AD 590/AD 592 lm phn t b nhit u ngui . Vit biu thc ng ra .

17. Tham kho data sheet IC AD595.Thit k mch o nhit T=0-10000C s dng thermocoupe loi K.M t chi tit thit k.

18. V s kt ni vi mch cm bin nhit DS1822(data sheet) vi MCU 8051 . Vit on chng trnh giao tip c nhit o v nhit ci t, bo qu/di nhit .


19. S dng IA AMP01 , analog sw v mch iu khin to thnh modul khuch i c lp

trnh vi h s khuch i n

vA 2 n=010. 20. Tham kho data sheet cm bin p sut STS-030A-4F.Thit k mch o p sut cho in

p ng ra V0 bin thin t 0-5VDC khi p sut tc ng bin thin t 0-30psi. 21. Mt cm bin p sut o tm t 0-10 bar cho ng ra l dng in t l tuyn tnh tng

ng t 4-20mADC.Thit k mch chuyn i tn hiu o p sut sang tn s ng ra t l 1 Khz/bar.

22. Cho mt cm bin load cell c cc thng s sau : - Cm bin c kt ni thnh cu Wheastone - Ngun cung cp max : 12VDC - Tng tr nhn t ng ra : 350 - Tm o max : 100Kg - nhy ton tm(E.S) ng ra : 2mV/V

Chn mch khuch i thch hp v c HSK m bo ng ra c nhy 10V/1g. 23. Mt mch d/ nhn dng mc cht lng hai mc cao thp nh hnh BT23

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