Ky Thuat Do Luong Ch2

7/30/2019 Ky Thuat Do Luong Ch2

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Gio trnh: kthuto lng 1 Dnh cho sinh vin nhm ngnh k thut

Bin son: PGS.TS. Nguyn Hu Cng Khoa in t -i hc K thut CN

Version1 - Thng 8 nm 2009

27

Chng 2

CC CCU CH TH

2.1. Ccu o cin

2.1.1. L lun chung v ccu o cin

2.1.1.1. Khi nim

Ccu o cin l dng co m s ch ca n l i lng t l vi i lngo lin tc, trong tn hiu vo l dng in hoc in p v tn hiu ra l gc quay

ca kim ch th. i lng cn o s trc tip bin i thnh gc quay ca kim ch th,

tc l thc hin vic chuyn i nng lng in t thnh nng lng chc lm quay

kim ch thi mt gc :

= f(x), x l i lng vo.

Ccu o cin bao gm hai phn: phn tnh v phn quay. Ty theo phng

php bin i nng lng in t ngi ta chia thnh ccu o kiu tin, in t,in ng, cm ng v tnh in.

2.1.1.2. Cc chi tit ckh chung ca ccu o cin

a) Trc v tr

Trc v tr l b phn quan trng trong cc chi tit ckh ca cc ccu o c

in, m bo cho phn ng quay trn trc c gn cc chi tit ca phn ng nh kim

ch th, l xo phn, khung dy.

b) B phn phn khng

B phn phn khng bao gm l xo phn khng hoc dy cng hoc dy treo.

Mc ch to ra mmen phn khng.

c) Kim chth gc quay

Kim ch th gc quay c gn vi trc quay. di chuyn ca kim trn thang

chia t l vi gc quay . Ngoi ra c th ch th gc quay bng nh sng.


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Hnh 2.1a. Mt s ccu phn khng

d) Thang chia

Hnh 2.1b. Thang chia

Thang chia l mt khc thang o, xc nh gi tr ca i lng o. C

nhiu loi thang chia khc nhau ty thuc vo cp chnh xc v bn cht ca ccu

o.

e) B phn cn du

B phn cn du c tc dng rt ngn qu trnh dao ng ca phn ng, xc lp

v tr cn bng nhanh chng trong ccu o.

a) Ccu cn du kiu khng kh b) Ccu cn du kiu

cm ng

Hnh 2.2. Mt s ccu cn du thng gp

Gng

L xo phn khng Dy cng Dy treo


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Thng thng c hai loi cn du c s dng, l cn du kiu khng kh v

cn du kiu cm ng.

2.1.2. Phng trnh c tnh ca ccu o cin

2.1.2.1. Cc mmen tc ng ln phn ng ccu

a) Mmen quay

Khi c dng in chy trong ccu o, trong n s tch lu mt nng lng in

t, nng lng ny c bin thnh cnng lm quay phn ng i mt gc no ,

thc hin mt cng chc:

dA = Mqd

trong : dA l lng vi phn ca cng chc;

Mq l mmen quay;

d l lng vi phn ca gc quay.

Theo nh lut bo ton nng lng:

dWe = dA

vi dWe l lng vi phn ca nng lng in t

Vy ta c: Mq = edWd. (2-1)

b) Mmen phn

Di tc dng ca mmen quay, nu khng c g cn li th phn ng ca c

cu s quay i mt gc ln nht c th c c. V vy ngi ta to ra cc mmen

phn t l vi gc quay nhcc b phn phn khng l l xo xon, dy cng hoc

dy treo.

Ta c: Mp = D; (2-2)vi D l h s ph thuc vo kch thc vt liu ch to l so, dy cng hoc dy treo.

Khi mmen quay cn bng vi mmen phn th phn ng ng yn

Mq = Mp = D.

c) Mmen ma st

i vi cc dng c dng trc tr ta phi xt n nh hng ca mmen ma st

gia trc v , mmen ma st c tnh theo cng thc kinh nghim


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Mms = K.Gn

(2-3)

trong K l h s t l, G l trng lng phn ng, n = (1,3 1,5).

d) Mmen cn duKhi trc quay dn n kim ch th quay theo cho ti v tr cn bng ri mi dng

li, do phn ng c qun tnh v b l xo ko li nn kim s dao ng ri mi ng

yn, kh khn cho vic c kt qu, cho nn phi c b phn n nh dao ng kim

hay cn gi l b phn cn du.

B phn cn du phi c ch to sao cho

mmen cn du c tr s t l vi tc quay ca

phn ng

Mcd = pd

dt

vi p l h s t l ph thuc vo c im cu to

ca b phn cn du. T biu thc trn ta thy khi

phn ng v tr cn bng thd

dt

= 0, nh vy

mmen cn du ch chng li s dao ng ca phn ng m khng lm nh hng

n kt quo lng.

2.1.2.2. Phng trnh cn bng phn ng ca ccu o

Theo nh lut chc: i vi mt vt chuyn ng quay, o hm bc nht ca

mmen ng lng theo thi gian bng tng cc mmen tc ng ln vt quay y. Do

, phng trnh cn bng mmen ca ccu o c dng:

2

i i2

d d dJ M J M

dt dt dt

= =

trong : J l mmen qun tnh ca phn ng;

Mi l tng cc mmen tc ng ln phn ng ca ccu, bao gm:

Mq =edW

d; Mp = D; Mms = K.G

n; Mcd = p

d

dt

.

Thay cc i lng trn vo phng trnh, ta c:

2

q p ms cd2

dJ M M M M

dt

=

Hnh 2.3. S dao ng ca kim


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2

p ms q2

d dJ p M M M

dtdt

+ + = . (2-4)

Phng trnh trn chnh l phng trnh chuyn ng cbn ca phn ng c

cu. Gii phng trnh ny ta tm c (t). Tu theo quan h gia J, P, D m ccu

dao ng hay khng dao ng v quyt nh tnh n nh v thi gian o ca ccu.

2.1.3. Ccu o tin

2.1.3.1. Loi c mt khung dy ng

a. Cu to

Phn tnh gm: nam chm vnh cu, cc t, li st non, trong khe hkhng

kh gia cc t v li st l u nhau.

Phn ng gm: khung dy, l xo phn, kim ch th.

Hnh 2.4. Ccu o tin

b. Nguyn l lm vic

Xt khi ta cho dng in mt chiu I chy vo khung dy, di tc dng ca t

trng nam chm vnh cu trong khe hkhng kh, cc cnh ca khung dy s chu

tc dng mt lc:

F = BlWI

Kim ch th

Cc t

Li st non

Khung dy

L xo

phn khng

Nam chmvnh cu


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trong : B l tr s cm ng t trong khe hkhng kh; l l chiu di tc dng ca

khung dy; W l s vng dy; I l tr s dng in.

Ta thy hai cnh ca khung dy cng chu tc dng ca lc F nhng ngc chiu

nhau nn s to ra mmen quay:

q

dM 2F B. .d.W.I B.S.W.I

2= = =l (2-5)

trong : d l kch thc ngang ca khung dy;

S = dl l thit din b mt khung dy.

Mmen phn ca l so: MP = D..

Vy phn ng s cn bng khi:

q P I

B.S.WM M B.S.W.I D I C .I

D= = = = . (2-6)

y IB.S.W

C constD

= = gi l nhy ca ccu theo dng in.

Ta thy t l bc nht vi I.

c.c im v ng dng

c im:

- u im:

+ Dng c c nhy cao v khng i trong ton thang o;

+ chnh xc cao, t chu nh hng ca t trng ngoi, tiu th nng

lng t;

+ V t l bc nht vi I nn thang chia ca ccu u.

- Nhc im:

+ Ch to kh khn, gi thnh t;

+ Do khung dy phn ng nn phi qun bng dy c kch thc nh

dn n kh nng qu ti km;

+ Cho c dng mt chiu. Tht vy, khi ta cho dng xoay chiu i =

Imsint vo khung dy, ta c mmen quay tc thi theo thi gian: mq(t) =

B.S.W.i = B.S.W. Imsint.


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T T

qTB q m

0 0

1 1M m (t)dt B.S.W.I sin tdt 0

T T= = = .

Vy mun o cc i lng xoay chiu ta phi kt hp vi b chnh lu.

ng dng:

Dng ch to ampemet, volmet o trong mch mt chiu; ch to ommet, in k

c nhy cao; dng lm ccu ch khng trong cc ng h vn nng, trong cc cu

o

2.1.3.2. Loi c hai khung dy ng (Logomet tin)

a. Cu to

- Phn tnh ging nh ccu mt khung dy nhng khe hkhng kh gia cc tv li st non l khng u nhau.

- Phn ng ta t hai cun dy cho nhau 60o, gn cng trn trc quay v ln

lt cho dng in I1 v I2 chy qua sao cho chng sinh ra hai mmen quay ngc

chiu nhau. Phn ng khng c l xo phn.

Hnh 2.5. Logomet tin

Khung dy 1

Khung dy 2I1I2


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b. Nguyn l lm vic

Khi ta cho cc dng mt chiu I1, I2 chy vo cc cun dy ng, di tc dng

ca t trng nam chm vnh cu s to ra cc mmen quay M1, M2 vi:

Mq1 = B1.S1.W1.I1;

Mq2 = B2.S2.W2.I2.

V khe hkhng kh l khng u nn cm ng t B ph thuc v tr ca khung

dy ng:

B1 = f1() Mq1 = f1().S1.W1.I1;

B2 = f2() Mq2 = f2().S2.W2.I2.

V khng c l xo phn nn phn ng s cn bng khi M1 = M2. Ta c:

f1().S1.W1.I1 = f2().S2.W2.I2.

Vy

1 1 1 2

2 2 2 1

f ( ).S .W I

f ( ).S .W I

=

.

Gii phng trnh ny ta tm c quan h: 2

1

If

I

=

. (2-7)

c.c im v ng dng

c im:

Tng t nh ccu mt khung dy trn nhng c chnh xc cao hn, cng

sut tn tht thp, nhy rt cao, t bnh hng ca t trng ngoi. Gc lch t

l vi t s hai dng in i qua cc khung dy, iu ny thun li khi o cc i

lng vt l thng phi cho thm ngun ngoi. Nu ngun cung cp thay i nhng

t s hai dng in vn c gi nguyn do vy m trnh c sai s.ng dng:

c dng ch to cc ommet, megommet.

2.1.4. Ccu o in t

Thc cht cng gm hai loi l ccu o in t thng thng v logomet in

t, tuy nhin loi logomet in t hin nay t s dng nn ta khng xt.


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2.1.4.1. Cu to

a) Ccu in t loi ht

b) Ccu in t loi y

Hnh 2.6. Ccu o in t

Ccu gm hai loi chnh nh hnh 2.6: kiu cun dy dt (ccu o in t loi

ht) v kiu cun dy trn (ccu o in t loi y). Ccu cun dy dt c phn

tnh l cun dy dt cho dng in cn o i qua, cn phn ng l mt l thp t

lch tm c th quay trong khe hcun dy tnh. Kiu cun dy trn c phn tnh l

Kim ch th

Khung dy

Trc quay

Ccu cndu

L thp di ng

L xo

phnkhng

I

kim ch l so


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cun dy trn bn trong gn mt l thp. Phn ng cng l mt l thp gn trn trc.

Ngoi ra cn c b phn cn du, l xo phn, kim ch th.

2.1.4.2. Nguyn l lm vic

Khi cho dng in chy vo cun dy tnh, trong lng cun dy s c mt t

trng. i vi cun dy dt t trng ny ht l thp vo trong lng cun dy tnh,

cn i vi cun dy trn th t trng s t ho hai l thp, khi hai l thp c cng

cc tnh nn y nhau. C hai trng hp trn s lm cho phn ng quay i mt gc

. Ta xt c th nh sau:

- Khi cho dng in mt chiu chy vo cun dy tnh:

Ta c mmen quay:

Mq =edW

d;

vi We l nng lng in t trng tch lucun dy

We =2

1LI

2

trong L l in cm ca cun dy v ph thuc vo ; I l dng in chy trong

cun dy.

Vy mmen quay:

Mq =2

1 dLI

2 d. (2-8)

- Khi cho dng in xoay chiu vo cun dy:

Gi s i = Imaxsin t. Lc mmen quay tc thi s l:

Mq(t) =2 2max

1 dLI sin t

2 d

.

Mmen quay trung bnh:

Mqtb =T T

2 2q max

0 0

1 1 dL 1M (t)dt I sin ( t)

T 2 d T=

dt

Mqtb =2

2

1I

d

dL

vi I l tr hiu dng ca dng hnh sin.

Ti v tr cn bng Mq = Mp;


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Mq = D2

1 dLI

2D d =

. (2-9)

Vy ccu o in t c tho c c dng mt chiu v dng xoay chiu.

2.1.4.3.c im v ng dng

c im:

- u im:

+ C cun dy phn tnh nn c th qun bng dy kch thc ln nn

kh nng qu ti tt.

+ D ch to, gi thnh h.

+ C tho c ci lng mt chiu v xoay chiu.

- Nhc im:

+ Gc quay t l vi bnh phng ca dng in nn thang chia khng

u (hnh dng l thp c ch to sao chodL

dgim theo gc quay

thang chia c th tng i u).

+ chnh xc thp do c tn hao trong li thp.

ng dng:

Ch yu o dng, p xoay chiu tn s cng nghip.

2.1.5. Ccu o in ng

2.1.5.1. Loi c mt khung dy ng

a) Cu to

Ccu gm hai cun dy. Cun dy tnh c tit din ln, t vng dy v thng

chia lm hai phn on. Phn ng l mt khung dy c nhiu vng dy v tit dinnh. Ngoi ra cn c kim ch th, b phn cn du, l xo phn.


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cun dy tnh

cun dy ng

Hnh 2.7. Ccu o in ng

b) Nguyn l lm vic

- Xt khi cho cc dng in mt chiu I1 v I2 vo cc cun dy phn tnh v

ng, trong lng cun dy tnh s tn ti mt t trng. T trng ny tc ng ln

dng in chy trong cun dy ng v to ra mmen quay:

Mq =edW

d.

Nng lng t trng tch lu trong lng cun dy l:

2 2

e 1 1 2 2 12 1 2

1 1

W L I L I M I I2 2= + +

trong L1, L2 l in cm ca cc cun dy v chng khng ph thuc vo gc quay

; M12 l h cm ca hai cun dy, thay i khi phn ng quay.

Mmen quay

Mq =e 12

1 2

dW dMI I

d d=

. (2-10)

- Xt khi hai dng in a vo cc cun dy l dng in xoay chiu th mmen

quay tc thi c tnh:

Mq(t) =12

1 2

dMi i

d.

Gi s i1 = I1msint v i2 = I2msin(t ).

Do phn ng c qun tnh khng kp thay i theo gi tr tc thi cho nn thc

t ly theo gi tr mmen trung bnh trong mt chu k:


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MqTB = T

o

q dt)t(MT

1

=T

121m 2m

0

1 dMI I sin t sin( t ) dtT d

=12

1 2

dMI I cos

d

vi l gc lch pha gia hai dng in; I1, I2 l cc gi tr hiu dng ca dng in

ln lt chy trong cc cun dy tnh v ng.

Tm li, trong mi trng hp ta u c:

12q 1 2 1 2

dMM I I cos K.I .I .cos

d= =

. (2-11)

Khi Mq = Mp12

1 2

dMI I cos

d

= D.

Vy 12 1 2 1 1 21 dM

I I cos K .I .I .cosD d

= =

. (2-12)

c)c im v ng dng

c im :

- u im:

+ chnh xc cao v khng c tn hao trong li thp.

+ C tho c ci lng mt chiu v xoay chiu.

- Nhc im:

+ D chu nh hng ca t trng ngoi.

+ Kh nng qu ti km v khung dy phn ng kch thc nh.+ Cu to phc tp, t tin.

+ Thang chia khng u (tr khi ch to wattmet).

ng dng:

+ Ch to cc ng ho dng, p xoay chiu c tn s cao hoc yu cu

chnh xc cao.

+ Ch yu ch to ng ho cng sut tc dng v phn khng.


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2.1.5.2. Loi c hai khung dy ng (logomet in ng)

a) Cu to

Phn tnh gm mt cun dy c chia lm hai na. Trong lng cun dy tnh c

hai cun dy ng gn trn trc quay cng vi kim ch th, khng c l xo phn.

Hnh 2.8. Logomet in ng

b) Nguyn l lm vic

Khi cho cc dng in xoay chiu i, i1, i2 ln lt chy vo cun dy tnh v cc

cun dy ng, trong lng cun dy tnh s c mt t trng. T trng ny s tcng ln dng in chy trong cc cun dy ng sinh ra cc mmen Mq1, Mq2

1q1 1 1

2q2 2 2

dMM I.I cos I, I

d

dMM I.I cos I, I

d

=

=

vi M1, M2 l h s h cm gia cun dy tnh v ln lt cc cun dy ng.

Ngi ta b tr sao cho cc mmen ny ngc chiu nhau, vy khi cn bng phnng, ta c Mq1 = Mq2

1 21 1 2 2

1 2 2

2

1 1

dM dMI.I cos I, I I.I cos I, I

d d

dM I cos I, I

d .dM

I cos I, I

d

=

=

i1

i

i2

Cun dy tnhKhung dy ng


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Gii phng trnh trn, ta c:

=

11

22

cosI

cosIf (2-13)

vi I1,I2 l cc gi tr hiu dng ca cc dng in i1, i2; 1, 2 l gc lch pha gia

dng in i, i1 v i, i2.

c)c im v ng dng

Ging nh c cu mt khung dy ng nhng ch yu ch to ng ho

cos 1 pha, 3 pha cho li in xoay chiu.

2.1.5.3. Ccu o st in ng v logomet st in ng

a) Ccu stin ng

Gm cun dy tnh, mch t nhm to ra t trng trong khe h khng kh.

Khung dy ng c gn vi trc quay cng kim ch th, l xo phn v b phn cn

du. Gc quay c tnh:

1 2 1 2KI I cos(I , I )= (2-14)

b) Logomet stin ng

Gm mch t c cu to sao cho to nn khe hkhng kh khng u, phn ng

gm hai khung dy t cho nhau 60o v gn trn trc quay cng vi kim ch th. Gc

quay c tnh:

2 2

1 1

I cos(I, I )f

I cos(I, I )

=

(2-15)

Hnh 2.9. Ccu st in ng Hnh 2.10. Logomet st in ng

i2

i1

i1

i

i2


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c)c im ng dng

- C tho dng mt chiu hoc xoay chiu. T trng qua khung dy ln nn t

chu nh hng ca t trng ngoi.

- Ccu o st in ng khc vi ccu o in ng ch c mch t lm

bng vt liu st t. V vy ngoi nhng sai s nh ccu o in ng, cn c thm

sai s do s c mt ca mch t gy nn. l sai s do t tr ca mch t, sai s do

tnh phi tuyn ca ng cong t ha B = f(H) khi dng co lm vic ch khc

nh mc. Xt khi ch to wattmet, do c mch t nn sai s gc ca wattmet st in

ng cng khc vi wattmet in ng. Trong ccu st in ng gc lch pha gia

t thng v dng in s ln hn nhiu so vi ccu in ng.

- Thng dng ch to cc dng co dng, o p, cng sut v gc lch pha.Ampemet v volmet st in ng thng ch to di dng dng co t ghi, loi

lp bng v mang xch chu va p.

Ccu o st in ng ng dng ph bin l ch to wattmet. So vi wattmet

in ng, wattmet st in ng cng kch thc c mmen quay ln hn v nhy

cao hn, nhng c nhc im l sai s ln hn.

2.1.6. Ccu o cm ng

2.1.6.1. Cu to

Ccu cm ng c cu to nh Hnh 2.11.

Hnh 2.11. Ccu o cm ng

1. Cun dy 1; 2. Cun dy 2; 3. Ccu cn du; 4. a nhm v trc quay

Ix1Ix2

F1F2

M12

M21

2

14


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2.1.6.2. Nguyn l lm vic

Khi cho dng in i1 vo cun dy 1 th cun dy 1 to ra t thng 1 xuyn qua

a nhm, dng in i2 vo trong cun dy 2 to ra t thng 2 cng xuyn qua a

nhm.

T thng 1 cm ng trn a nhm sc in

ng e1 chm pha hn 1 mt gc /2.

T thng 2 cm ng trn a nhm sc in

ng e2 chm pha hn 2 mt gc /2.

V a nhm c coi nh rt nhiu vng dy

t st nhau, cho nn E1, E2 s

to ra trn

a nhm

cc dng in xoy ix1 v ix2 chm pha hn so vi e1

v e2 cc gc 1 v 2 v ngoi in trthun cn c

thnh phn cm ng, tuy nhin do cc thnh phn

cm ng rt nh nn ta gi thit cc gc 1 v 2

0.

Do c s tng h gia t thng 1, 2 vi cc dng in ix1 v ix2 m sinh ra cc

lc F1 v F2 v cc mmen tng ng lm quay a nhm.

Ta xt cc mmen thnh phn nh sau:

M11 l mmen sinh ra do 1 tc ng ln ix1



M22 l mmen sinh ra do 2 tc ng ln ix2.

Gi tr tc thi ca mmen quay M1t do s tc ng tng h gia 1 v dng tc

thi ix1 l:

M1t = C1ix1

vi C l h s t l.

Gi s: 1 = 1m sint

ix1 = Ix1m sin(t )

vi l gc lch pha gia 1 v ix1, ta c:

M1t = C1mIx1m sint sin(t ).

Hnh 2.12. th vect


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V phn ng c qun tnh cho nn ta c mmen l i lng trung bnh trong

mt chu k T:

M =

T T

1t 1m x1m

0 0

1 1

M dt C I sin t sin( t )dtT T=

= C1Ix1cos.

Nu ta coi cc gc 1 v 2 0, xt ln lt cc mmen trn

M11 = C111Ix1 cos (1, Ix1) = C111Ix1 cos (/2) = 0

M12 = C121Ix2 cos (1, Ix2) = C121Ix2 cos (/2 + ) = C121Ix2 sin

M21 = C212Ix1 cos (2, Ix1) = C212Ix1 cos (/2 ) = C212Ix1sin

M22 = C222Ix2 cos (2, Ix2) = C222Ix2 cos (/2) = 0.

Nh vy mmen quay s l tng cc mmen thnh phn M12 v M21 c du

ngc li:

Mq = M12 + M21

do vy mmen tng s ko a nhm v mt pha duy nht:

Mq = M12 + M21 = C121Ix2 sin+ C212Ix1sin

Nu dng in to ra 1 v 2 l hnh sin v a nhm l ng nht(ch c in trthun) th cc dng in xoy Ix1 v Ix2 s t l vi tn s v t thng sinh ra n, tc l:

Ix1 = C3f1; Ix2 =C4f2.

Do vy Mq = C121 C4 f2 sin+ C212 C3f1 sin

= (C12C4 + C21C3) f12 sin

= Kf12sin

vi K = C12C4 + C21C3 l hng s ca ccu o cm ng.Tm li ta c: Mq = Kf12sin (2-16)

Nu c l xo phn, mmen phn ca l so: MP = D., khi cn bng phn ng ta c:

= K112sin. (2-17)

2.1.6.3.c im v ng dng

iu kin c mmen quay l phi c t nht hai t thng hoc hai thnh phn

ca cng mt t thng lch pha nhau v khng gian v thi gian. Mmen quay cc i

khi sin= 1, c ngha l gc lch pha gia hai t thng 1 v 2 l /2.


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45

Mmen quay ph thuc vo tn s v in trca a nhm nn khi tn s thay

i hoc nhit thay i th chnh xc khng cao.

Ccu c ng dng ch yu ch to cng to nng lng tc dng v

phn khng trong li in xoay chiu.

2.2. Ch th s

2.2.1. Khi nim v nguyn l cbn ca ch th s

Trong nhng nm gn y xut hin v s dng rng ri cc ch th s, u vit

ca ch th s l thun li cho vic c ra kt qu, ph hp vi cc qu trnh o lng

xa, qu trnh tng ho sn xut, thun li cho nhng i thoi gia my v ngi.

S khi ca ch th s c th tm tt nh sau:

Hnh 2.13. S khi ca ch th s

i lng o x(t) qua b bin i thnh xung (BX), s xung N t l vi ln

x(t) c a vo b m ho (MH), b gii m (GM) v b hin s. Cc khu m ho,

gii m, b hin s to thnh b ch th s.

2.2.2. Ch th s

C nhiu loi ch th s khc nhau nhng ph bin hin nay vn dng ch th s

n phng in nhiu cc v ch th s ghp 7 thanh bng it pht quang hoc tinh

th lng.

2.2.2.1. Chthn phng in nhiu cc

Ch th l mt n nng c mt anot v 10 katot. Anot thng t in p220V - 250V. Katot c ch to bng dy Cr-Ni un thnh hnh cc ch s t 0 - 9.

Mi katot l mt con s.

Khi c in p gia anot v mt katot no n s phng in, katot s sng

ln v con s xut hin.

- u im ca ch th ny l hnh dng cc con sp.

- Nhc im: Kch thc cng knh, ngun in p cung cp cao, ch ph hp

trong cng nghip.

x(t) BX M hoB hin s

Gii m


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Bin son: PGS.TS. Nguyn Hu Cng Khoa in t -i hc K thut CN 46

2.2.2.2. Chthsghp 7 thanh

Hnh 2.14. S nguyn l ca LED 7 thanh

Ch th ny c ghp bng 7 thanh dng it pht quang (LED: Light Emitting

Diode) hoc tinh th lng (LCD: Liquid Crystal Display).

it pht quang l nhng cht bn dn m pht ra nh sng di tc dng ca

dng in mt chiu. Tinh th lng l nhng mng mng lm bng cht tinh th lng. l nhng cht di tc dng ca in p mt chiu chuyn pha t dng lng sang

dng tinh th v ngc li. Khi dng tinh th, thanh ny trnn trong sut, ta c th

nhn thy mu sc nn ng sau.

Mt u im cbn tinh th lng tiu th dng in rt nh: 0,1A/thanh, trong

khi it pht quang c: 10mA/thanh.

Trong thc t cn ch th s 16 thanh, ma trn im

A K

a

b

cd

e

fg

a

bcdefg

A chung +5V

Mt it pht quang

Cc katot

tng ng vicc it

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