CHNG 2CC PHN T C BN CA DNG C OMi dng c o c bn (hnh 2.1) c 3 b phn chnh l:-Chuyn i s cp (CSC). -Mch o (M). -C cu ch th (CCCT).Chuyn i s cp (CSC): thc hin chc nng bin i cc i lng o thnh tn hiuin. L khu quan trng nht ca mt thit bo, quytnh chnh xc cng nh nhy ca dng c o. C nhiu loi chuyn i s cp khc Mcho(M): thchinchcnngthuthp, giacngthngtinosaucc chuyn i s cp; thc hin cc thao tc tnh ton trn s mch. Ty thuc dng c o l kiu bin i thng hay kiu so snh m mch o c cu trc khc nhau. Cc c tnh c bn ca mch o gm: nhy, chnh xc, c tnh ng, cng sut tiu th, phm vi lm vic.. c xt c th cho mi loi mch o c thit k ph hp cng nh s dng c hiu qu. Mch o thng s dng k thut vi in t v vi x l nng cao cc c tnh k thut ca dng c o. -C cu ch th (CCCT):l khu cui cng ca dng c o, thc hin chc nng th hin kt qu o lng di dng con s so vi n v sau khi qua mch o. Cc kiu ch th thng gp gm: ch th bng kim ch, ch th bng thit b t ghi (ghi li cc tn hiu thay i theo thi gian), ch th di dng con s (c trc tip hoc t ng ghi li)Ch th tng t (ch th c in) thng dng trong cc thit b o dng, in p, tn s, cng sut, gc pha ... i lng cn o c bin i trc tip thnh gc quay ca phn ng (bin nng lng in t thnh nng lng c hc lm quay phn ng mt gc lch so vi phn tnh). Ch th tng t gm c: T in, in t, in ng, cm ng v.v...Ch th t ghi: S dng cc dng c t ghi nhm mc ch ghi li nhng tn hiu o thay i theo thi gian.Ch th s: Biu din bng s cc gi tr thng s trng thi o c. T tn hiu tng t chuyn sang tn hiu s phi qua mt b bin i xung mch 19Hnh 2.1: Cu trc c bn ca mt dng c oCSC MCCCTKt qu o Tn hiu o m mch m ho gii m ch th. Thc hin ch th s c nhiu cch: ch th hunh quang, s ghp bng diod pht quang hay tinh th lng v ng phng tia in t.$2.1 CC C CU HIN TH2.1.1. C cu ch th tng t1. Khi nim chunga) Nguyn l lm vicCh th tng t (ch th c in) c i lng u ra (kt qu o) lin tc t l vi tn hiu cn o. Cc c cu o c in tuy khc nhau v nguyn l hot ng nhng u ging nhau mt im v cu to bao gm hai phn chnh: phn tnh v phn ng.Cc c cu o c in u c i lng u ra l gc quay ca phn ng , c s bin nng lng in tthnh nng lng c hc lm quay phn ng mt gc lch so vi phn tnh. Khi cho dng in i vo c cu o c in, trng in t tc ng ln phn ng ca c cu sinh ra mmen quay. Mmen ny c xc nh bng t s gia s thay i ca nng lng in t c tch lu trong c cu vi s thay i gc quay ca phn ng: ddMqtWNu trn trc quay phn ng c gn l xo cn th khi phn ng quay n s b xon li sinh ra mmen cn MC. Mmen ny t l thun vi gc quay ca phn ng c gi tr c xc nh theo biu thc: D MC Nh vy phn ng s quay di hiu ca hai mmen ny. Khi hai mmen cn bng phn ng s dng li vi gc lch so vi v tr ban u:ddD M MC qtW Vy ddDtW 1b. Nhng chi tit v b phn chung ca c cu o c inCc c cu o c in khc nhau c nguyn l lm vic khc nhau nhng chng c nhiu chi tit v b phn tng i ging nhau nh: trc quay v gi trc quay, l xo cn, b phn cn du, thang o v kim ch th v.v.. Trc quay v gi trc quayTrcquaylmbngthphpkimOsimi Hay Iridi c cng v chng mi mn cao. Trc c ng knh t 0,8 1,5mm, u trc c 20Hnh 2.2 Nhng chi tit chung ca c cu o c inKimThang oL xo cnL xo cnTrcGi dng hnh nn vi gc nh t 450 600. Tn cng nh trc c dng bn cu, bn knh 0,05 0,3mm. trc c da trn gi .Gi trc quay lm t cng(rubi). Ni trc c khot lm hnh nn vi gc nh l 800. nh c v thnh hnh chm cu bn knh 0,15 0,5mm. Thng mt c cu c hai gi . Mt c g c nh, mt c th iu chnh c ln xung m bo kht gia trc v gi .L xo phn khng (l xo cn)L xo to ra mmen cn trong cc c cu o c in. N thng c hnh dng xon c, mt u gn ng vi trc quay, u cn li gn i b phn iu chnh v tr 0 ca im, c nh trn phn tnh. Mi c cu thng c hai l xo gn trn hai u trc quay, c chiu xon ngc nhau. Ngoi chc nng to ra mmen cn, l xo cn c nhim v dn in vo cun dy, nu cun dy nm trn phn ng.L xo c ch to t hp kim ng berili hoc ng -pht pho c n hi tt v n nh.Trong c cu o c nhy cao, gim ma st, ngi ta thay h thng trc, gi v l xo phn khng bng cc thanh treo hoc cng c tnh n hi. Thanh treo hoc cng c dng l hnh ch nht dng treo hoc cng c nh phn ng, khi phn ng quay n b xon li sinh ra mmen cn.Kim ch th v tia sng ch thKimch th gcquaygncngtrntrcquay. Kimphinhvcngnn thng cch totnhm v hp kimcan. Hnhdngcakimtu thucvocpchnhxccadngc v khong cch ti mt ngi c kt qu o.Cc thit b ocnhycao, ngi ta thaykimobngtia sng mnh. Ccudngtiasnglmkim ch th c mt h thng quang hc gm: ngun sng, h thng thu knh, gng phn x gn trn phn ng v mt s gng phn x khc.Thang chia Trn tm mt mu trng ngi ta in ng thang l cung trn mu en. Trn ng thang c in cc vch chia v ch s ch gi tr o tng ng vi cc vch chia .B phn cn duB phn cn du l mt chi tit c tc dng dp tt dao ng ca phn ng khi o. N lm gim thi gian n nh, cho ta c nhanh kt qu o. 21Ngun sngGngThang oHnh 2.3 H thng tia sng ch thC hai loi cn du kiu khng kh v cn du kiu cm ng. Hnh2.4lbphncndukiu khng kh bao gm mt hp kn trong c mt l nhm mng chuyn ng, l nhm c gn cng vi trc quay. Khi phn ng dao ng l nhm qut trong hp kn. Lc cn khng kh tc ng ln l nhm s dp tt dao ng. Khi phn ng n nh th cng khng cn lc cn ny nn b phn cn du khng nh hng n php o.2. C cu o t ina) Cu toCutocaccuotin c m t nh hnh 2. 4.Phntnhbaoca ccugm mt nam chm vnh cu v h thng mch t lmtcc khistnon c hnhdngcbit ghpli tonn khehkhngkh hpvugia khi st non hnh tr nm gia v hai khi st non nm hai bn.Phnng: lkhungnhmhnh ch nht trn khung c qun dy ng bc lp cch in nh. Ton b khi lng khung quay phi cng nh cng tt sao chommen qun tnh nh. Khung quay c t trn trc quay hoc dy treo. Trn trc quay c gn kim o v l xo phn khng. C cu o t in khng cn b phn cn du dp tt dao ng ca kim o v trong khung nhm c dng in xoy khi n dao ng trong t trng. Dng ny kt hp vi t trng to ra mmen dp tt dao ng. .Mt khc khi cun dy dao ng trong t trng cng lm xut hin trong n mt dng in cm ng c tc dng tng tb) Nguyn l lm vic Tc ng vi dng mt chiu22Hp knL xo cnL nhmKim oVHnh 2.4 B phn cn du kiu khng khtrcCc tL xoKhung tThang oKim oKhi st hnh trKhung dyphn ngHnh 2.5: C cu o t inKhi cho dng in mt chiu I i vo trong cun dy s xut hin lc in t tc ng ln cc cnh nm trong t trng ca cc vng dy. Nu cun dy c W vng th lc in t tc ng ln mt cnh khung dy l:W l I B F . . . Trong : B l cm ng t trong khe h khng kh; l l chiu di tc dng ca vng dy.Mmen quay tc ng ln phn ng l:S I B W W b l I B b FbF Mq. . . . . . . .2. 2 Vi b- l chiu rng ca khung dy. S- din tch ca khung dy.Nu tS W B K . .. =const th Mq =K1IDi tc dng ca mmen quay, phn ng s quay i mt gc lm cho l xo xon lisinh ra mmen phn khng: D MC Trong D l hng s xon ca l xo.Phn ng ngng quay khino mmen quay do dng in to ra v mmen cn do l xo gy nn cn bng vi nhau :q CM M HayI K D . . Vy phn ng s quay c mt gc:I K IDK.1 Trong K l hng s. Nh vy gc quay ca phn ng t l bc nht vi dng in. nhy ca c cu o t in KI Is . Tc ng vi dng xoay chiuKhi c dng in xoay chiu i = Imsin t i vo cun dy th mmen quay tc ng ln khung dy cng bin thin hnh sin. Mq =K1i =K1Imsin t 23Hnh 2.6 C cu o t inK hiu Nguyn l lm vicPhn ng c qun tnh nn khng th quay theo mmen ny c. V vy c cu o t in khng o c dng xoay chiu.c) c im v ng dng-C cu o t in c nhy cao do c t trng trong khe h khng kh mnh. Kt qu o khng b nh hng bi t trng ngoi. Cng sut tiu th nh. C cu o t in c dng ch to dng c o c chnh xc cao (c thtc cp chnh xc 0,5%).Vgcquay tuyn tnh theo dngin nn thang o c khong chia u.- Nhc im: C cu c cu to phc tp nn gi thnh cao, kh nng chu qu ti km do tit din dy nh. C cu khng o c dng in xoay chiu.-ngdng : Ccuch th tindngchtoampemt mt chiu, vnmt mt chiu v m mt vi chnh xc cao. Ngoi ra c th kt hp vi cc b chnh lu o dng in xoay chiu. Hoc c th lm cc b ch th trong cc mch o cc i lng khng in.d) Lgmt t inTrn c s ca c cu ch th t in ngi ta sng to ra mt loi c cu ch th o t s gia hai dng in l lgmt t inL gmt t in c cu to v nguyn l hot ng ging c cu o t in Phn tnh ca n c khe h khng kh l khng u do khi st non gia c hnh tr khuyt hoc ovan. Phn ng khng c l xo cn, thay vo c mt khung dy th hai to ra mmen c hng chng li mmen quay ca khung dy th nht (hnh 2.6)Phn ng trong khe h mch t ca nam chm vnh cu gm hai khung dy t lch nhau mt gc no ddI M11 1 ;ddI M22 2 Khi c s cn bng ca hai mmen ny th phn ngs dngdtdIddI2211Suy ra ) () () (//122121 fffd dd dII C th ly hm ngc ca hm trn nh sau:) (21IIF Gc lch ca t l k t in t l vi t s gia hai dng in. Nu hai dng ny u o cng mt ngun in p to ra v u t l bc nht vi in p th s khng ph thuc vo in p. 24Hnh 2.7: Lgmt t inI1I23. C cu o in ta) Cu toC cu o in t lm vic da trn s tng tc v lc gia dng in trong cun dy to ra vi vt st b t trng t ha hoc gia hai vt st t cng b t trng ca cun dy t ha.C cu o in t cng c chia thnh hai phn: phn tnh v phn ng. Phn tnh gm cun dy v l thp c nh gn trong mt trong ca cun dy. Phn ng gm l thp ng, trn trc quay c gn kim, l xo phn khng v c cu cn du kiu khng khb)Nguyn l lm vicKhi c dng in chy trong cun dy th c hai l thp b t ho cng cc nn chng y nhau to nn mmen quay. Mmen quay do lc y gia hai l thp lm cho phn ng quay, n l t s gia s gia ca nng lng t trng dWt tch lu trong h thng vi gia s gc quay dca phn ng.22t22WIddLdLIdddMq Ngi ta thit k sao cho 12KddLlhngs,nhvy:Mq = K1I2Khi phnngquay, lxo xon li sinh ra mmen cn MC =D . Gc quay ca phn ng c xc nh:2 2 1KI IDK Nhvygcquay tl vi bnhphngcacng dngin. Ccuoint tcngcvidnginmt chiu v xoay chiu.c)c im v ng dng- C cu o in t tiu th nng lng nhiu hn c cu o t in. Gc quay ca c cu t l vi bnh phng dng in nn thang o khng tuyn tnh. nhy thp do in cm ca cun dy nh. C cu c chnh xc khng cao do c hin tng t d trong l st non v chu nhiu nh hng ca t trng bn ngoi- Tuy nhin c cu chu c qu ti cao, cng ngh ch to d hn c cu o t in nn thng c dng ch to vnmt v ampemt o p v dng xoay chiu tn s thp.25Hnh2.7: C cu o in tK hiuS cu to Hnh 2.8: C cu o in tk hiuS cu to4 C cu o in nga)Cu toPhn tnh ca c cu o in ng gm cun dy A c chia thnh hai phn on A1v A2c th mc ni tip hoc song song vi nhau to ra t trng mnh tp trung tm cun dy khi c dng in chy qua.Trc quay chui qua khe h gia hai cun tnh.Phnng: lcundyBnmtronglngcundytnh. Cundyng thng khng c li st non trnh c hin tng t tr v dng in xoy. Trn trc cn c l xo phn khng, b phn cn du v kim ch th. C phn tnh v ng u bc kn trong mt mn chn t c cu khng b nh hng bi t trng bn ngoi.Nu cun dy c nh qun trn li st t l c cu st in ng (hnh 2.9)b)Nguyn l lm vicVi dng in mt chiuKhi cho hai dng in mt chiu I1v I2i vo hai cun tnh v ng, nng lng t trng tch lu trong hai cun dy s l:2 1 1222 221 12121I I M I L I L Wt+ + Vi L1, L2 l in cm ca cc cun dy tnh v ngM12 l h s h cm gia cc cun dy. N ph thuc vo v tr tngi giacccun dy.Mmen quay do cc dng in tng tc vi nhau:26CuntnhCun ng CuntnhHnh 2.10: C cu st in ngCun ngL xoKimL xoHnh 2.9 C cu in ngCun tnhThang oHnh 2.11 C cu o in ng a) K hiub) S cu to2 112 tWI IddMddMq Ti v tr cn bng mmen quay bng mmen cn, nn ta c:2 112I IddMD Vy 2 1121I IddMD Vi dng in xoay chiuCho dng in i1 = I1msin t vo cun tnh A v dng in i2 = I2msin( t+ ) vo cun ng B th mmen quay trung bnh tc ng ln phn ng l cos ) sin( sin12 112 12)2 1I IddMdtddMt t I ITMTm m q + Khi cn bng ta c: cos12 112I IddMDc) c im v ng dngC cu o in ng c u im v khuyt im ca c cu t in v in t.u im:- C cu o in ng c th dng lm dng c o trong mch mt chiu v xoay chiu.- C cu o in ng c chnh xc cao khi dng trong mch xoay chiu v khng dng cht st t nn loi b c cc sai s do dng in xoy v t tr gy ra.Nhc im:- Gc quay ca c cu ph thuc vo tch I1I1 nn thang o khng u- C cu o in ng c cng sut tiu th ln nn khng thch hp khi o ccmchincngsut nh. nhythpdommenquaykhnglnv t trng khp kn qua khng kh c t tr cao.d) Lgmt in ngT l k in ng c cu to phn tnh hon ton ging c cu ch th in ng. Phn ng gm hai khung dy t cho nhau mt gc v gn trn trc cng vi kim o. Ging nh t l k t in, t l k in ng khng c l xo cn (hnh 2.10).Khi cho dng in I i vo cun tnh A, cc dng in I1, I2i vo cc cun ngB1, B2. Cuntnhstcngvihaicun ng to ra hai mmen quay M1 v M2 ngc chiu nhau : ddMII M011 1 1cos 27Hnh 2.12: Lgmt in ngddMII M022 2 2cos Trong 1; 2 l gc lch pha gia I1, I2 vi I.M01, M02 l h s h cm gia cc cun ng B1, B2 vi cun tnh A. o hm ca chng theo gc quay cng l cc hm ca gc quay ny.) (101fddM ;) (202fddMHiu ca hai mmen ny lm phn ng quay. Trong qu trnh quay khi chng cn bng nhau th phn ng s dng li.) ( cos ) ( cos2 2 2 1 1 1 f II f II 1 12 221coscos) () () (IIfff Ly hm ngc ta c )coscos(1 12 2IIF 5. C cu o cm ngCcuocmnghot ngdatrns tngtc vlcgia cc ttrng xoay chiu cahai haynhiucundyvi ccdngin xoy do cc t trng ny sinh ra trong mt a kim loi.1. Cu toC cu o cm ng bao gm hai phn: tnh v ng:- Phn tnh gm hai nam chm in 1, 2- Phn ng gm a nhm mng 3 gn trn trc quay 4. Trc ny c bng gi 5. Phn ng quay da trn s tng h gia t trng xoay chiu v dng in xoy to ra trong a nhm. Do c cu o cm ng ch lm vic vi dngxoay chiu.2. Nguyn l lm vicKhi cho cc dng in xoay chiu I1, I2 chy vo cc cun dy phn tnh s sinh ra cc t thng 1,2. Cc t thng ny cng lch nhau mt gc ging nh cc dng in.Cc t thng 1,2xuyn qua a nhm lm xut hin trong a nhm cc sc in ng cm ng E1, E2 lchphavi tthnglnlt mt gc /2.Tcdng tng h gia t thng v cc dng in xoy trong a 2834512\2\Hnh 2.13:C cu o cm ng12I1I212E1E2Hnh 2.14: th vctnhm l cc lc F1, F2 tc ng ln a nhm. Tng hp hai lc ny to ra mmen quay a nhm. Mmen ny c xc nh theo biu thc: Mq = Cf 1, 2 sin .3. c im v ng dng- iu kin c mmen quay tc ng ln c cu cm ng l phi c t nht hai t trng xoay chiu.- Mmen quay t gi tr ln nht khi gc lch pha gia hai t trng t /2Mqmax = Cf 1, 2 sin900 =Cf 1, 2 - Mmen quay ph thuc vo tn s ca cc dng in to ra t trng- C cu cm ng ch tc ng vi dng in xoay chiuBng 2-1S TTTn c cu K hiu Tn hiu ong dng1 T in I-A, V, , G2 T l k t in I1-/ I2-M , dng c o khng in3 in t I2 A, V4 in ng I1, I2 A, V, W5 T l k in ng I1/ I2 cos-mt, tn s k6 Cm ng I1, I2 Cng t - mtBng 2.1 trn trnh by tm tt k hiu ca cc c cu o kiu c in, tn hiu m chng o c v ng dng ca chng.2.1.2.C CU CH TH T GHI1 Nguyn l chung29Cc dng c t ghi nhm mc ch ghi li nhng tn hiu o thay i theo thi gian. Ph thuc vo tc ghi m ta c th phn ra lm ba loi: C cu ch th t ghi c tc thp, c cu ch th t ghi c tc cao, c cu ch th t ghi c tc rt cao.Khi tn hiu cn o c tn s thp (di 10Hz), ngi ta thng s dng cc loi ch th t ghi c tc thp. l cc bt ghi vch ln bng giy chuyn ng vi tc u. Cc c cu ch th s dng l c cuch th t in v st in ng.Dng c t ghi c tc ln ( tn s di 100Hz) thng s dng cc ch th t in hoc in t.i vi cc loi dng c t ghi c tc ln (tn s trn 100Hz), ta c th s dng c cu c in c tn s dao ng ring cao. Khi tn s tn hiu cn o rt cao (trn 800Hz) ngi ta thng s dng c cu ch th in t nhm mc ch quan st, nh v ghi li mt on tn hiu. Cc dng c l cc dao ng k in tTrong phm vi chng trnh ta ch xem xt n dao ng k in t, l mt loi dng c o cc i lng bin i theo thi gian thng dng nht hay c s dngtrongngnh. Haycncgi vici tnlmyhinsng(Electronic osiloscope) 2 ng phng tia in t (cathode ray tube-CRT):l b phn ch th ca dao ng k in t (Hnh 2.13).ng phng tia in tgm 1 bu thu tinh ht ht chn khng. Trong ng c t mt cathode c si nung (tim n), cc anode A1, A2 v li iu khin. Cc chi tit ny to nn mt b phn c gi l sng phng tia in t. Bn cc gia tc A1, A2 c nhim v lm tng tc cho chm tia in t.30Tim nBn lch dc XBn lchNgang YMn hunhquangBUA1Lp than chHnh 2.15: ng phng tia in tA2Ngoi sng phng tia in t, trong bu thu tinh cn t hai bn cc phng l bnlchdcvbnlchngang: Khi chmtiainti quabnlchdcv ngang, th in trng gia hai bn cc ny s li chm tia in t lch theo chiu dc v chiu ngang bng lc tnh in. lch ca chm tia in t theo chiu dc hoc ngang ph thuc vo in p gia hai bn cc.Mn hunh quang mt trong ca mn nh ng CRT c ph mt lp pht quang, ty theo vt liu ca lp pht quang ny m tia sng pht ra khi chm tia n tp vo mn nh hunh quang c mu sc khc nhau. Lp than ch xung quanh ng cnh mn nh thu nhn cc in t p vo mn nh di tr li. Do in th m khng tch t li mn nh.Nu ta t mt in p xoay chiu vo hai bn cc ngang Y, tia in t s di chuyn ln xung theo chiu thng ng ta s nhn thy mt vch sng thng ng nm gia mn hnh.Nu ta t mt in p xoay chiu vo hai bn cc dc X, tia in t s di chuyn sang phi sang tri s nhn thy mt vch sngnm ngang gia mn hnh.Nu a ng thi hai tn hiu in p hnh sin cng tn s v bin vo cc cp li tia ng v ngang, ta s nhn c trn mn hnh mt ng khp kn c hnh dng tu theo lch pha gia hai tn hiu in p. ng cong nh vy gi l Lissajous.Dao ng k in t thng c ng dng quan st cc loi tn hiu khc nhau c di tn rng. Ngoi ra c th s dng o in p, tn s v o gc lch pha.Dao ng k in t hin i c th c hai hoc nhiu tia in t c ci t b vi x l nh li mt on tn hiu v c th iu khin a tn hiu ra my in hoc ghi ra bng hay a t lu gi.31Hai tn hiu cng tn s, cng phaHai tn hiu cng tn s, lch pha 1800Hai tn hiu cng tn s, lch pha 900Tn s ca tn hiu ngang = 2 ln tn s tn hiu qut dcHnh 2.16: Hnh Lissajous o s lch gia hai tn hiu2.1.3 C CU CH TH S 1 Nguyn l chung ca dng c ch th sCu trc chung ca mt dng c o k thut s c m t nh hnh 2. 17Tn hiu vt l cn o c a vo b chuyn i o lng s cp c bin i thnh tn hiu in. Sau tn hiu c s ho a vo b m ho x l(chuyngi tr thpphnsangnh phn). Tip n tn hiu c a n b gii mphchi vdngtngt ban u. Cui cng c a ra b hin s.2. Thit b hin sThit b hin th s ch th gi tr ca i lng cn o dng thp phn v n v o hay khong o cng cc thng tin khc nhm em tin li cho ngi s dng. Cn thit phi thc hin chuyn m t nh phn sang BCD v hin th bng c ch in quang hoc ch th bng my tnh. Ch th cho thit b o s c nhiu loi khc nhau nh:-ch th s dng h thng c in, c in quang-ch th s dng h n si nung cng sut nh-ch th s dng n s loi c kh-ch th s dng linh kin c hiu ng quang-ch th s dng it pht quang (LED)-ch th s dng linh kin l tinh th lng (LCD)a) B ch th s dng h thng c in:Cc i lng sau bin i ri rc (s) c tip tc bin i thng qua cc thit b nh: ng c chp hnh, ng c bc, rle in t...m to ra cc lc chuyn ng c hc lm quay cc trng s. Mi trng s c nh s t 0-9 c vai tr mt hng trong h m 10Nhc im ca b ch th ny l:- Tc thip lp thp do c qun tnh ln khong 2-20km/s32Tn hiu o C s cp Bin i tn hiuHT sHnh 2.18: M ha tn hiuHnh 2.17: Cu trc chung ca mt dng c o k thut s- Kch thc cng knh, ch s kh cb) C cu ch th s bng LED 7 thanh dng it pht quang (LED)L loi thit b s c s dng rt ph bin v nguyn l n gin, d s dng, tin cy cao v gi thnh thp.Cu to: Hnh 2.19 cho thy cu trc ca mt n LED 7 thanh, gm 7thanh mng ghp li thnh hnh ch s 8 (k hiu t a g), Mi thanh l 1 it pht quang(LED), tngngcccuracptn hiuchotngit, ccit cthniantchung hay catt chung. Khi c tn hiu cho php it no hot ng th it s sng, phi hp s sng ti ca cc it s cho ra cc con s: 0-9, cc k hiu, cc k tit pht quang (Light-emitting - diode): Llinhkindngchth s thng dng hin nay. LED l cc it bn dn pht x nh sng khi c dng in chy qua (hnh 2.20). LED c nhiu im vt tri nh tn s hot ng cao, th tch nh, cng sut tiu th b. c nh sng mu, ngi ta dng cc loi bn dn khc nhau.Mt ch th s s dng LED 7 thanh c mt s cu trc sau:in p thun ri trn mi it ca mi thanh khong 1,2V v dng thun qua LED tngng vi sng thch hp vo khong 20mA ty ln ca LED. Nhc im chnh ca LED 7 thanh l yu cu dng ln.Trong cc b hin th dng LED 7 thanh c th mc theo 2 cch anod chung hoc cathode chung33Hnh 2.19 Hnh dng LED7 thanhHnh 2.20: : it pht quang LEDHnh 2.21: mt s dng ch th LED 7 thanhV d: Mt b gii m dng cho LED 7 thanh.thchinch th schob nhthpphnphi sdngmch gii m(hnh2.23). Ccuraca b m c a ti mch gii m v araiukhinchoLED7thanh pht sng lin tc trong thi gian hin th. y mch gii m s dng l vi mch 4511 c dng iu khin mt b ch th LED c chung cathode. mbo dng mong mun cn phi c thm 7 in tr bn ngoi. c) B ch th dng tinh th lng (LCD)Tinh th lng l tn trng thi ca mt vi hp cht hu c c bit nh: matic, stematic... cc cht lng ny nng chy hai trng thi: nht thp LCD trng thi ng bng, nhit cao LCD trng thi ng hng. Pha trung gian gia hai trng thi ny (00C n 60 0C) l trng thi tinh th lng (liquid crystal display), n va c tnh cht lng va c tnh cht tinh th.Cu trc ca mt ch th tinh th lng nh sau:34Cha c in p t voKhi c in p t voHnh 2.24: Hin th s tinh th lng LCDHnh 2.23: Mch gii m dng cho LED 7 thanhHnh 2: 22: Cch mc LED 7 thanhN bao gm mt lp thu tinh lng nm gia hai tm knh. Hai tm nha phn cc dn trc v dn sau tm knh c s phn cc ng bng 900. Nh vy nh sng phn cc khi i qua lp tinh th b xoay i 900.Khi cha c in p xoay chiu t vo, mt ch th trong sut. Khi c in p xoay chiu (khong vi vn) t vo, cc phn t tinh th nh hng heo hng ca in trng. Nh th s xoay ca nh sng phn cc qua tinhthlngb trit tiu, nhsng khng th i qua mng lc phn cc thhai. Nhthontinhthlng chunhhngcaintrngti i. Vi hai mng lc c s phn cc mt gc en. Nu hai mng lc phn cc song song, ta c nn en v ch s trong.Mt ch th ssdngLCDc mt s cu trc nh hnh 2.25.u im ca thit b hin th tinh th lng l tiu th dng rt nh, c 7 thanh ca hin th tinh th lng loi nh ch yu cu dng khong 80A.357 thanh16 thanhMa trn 5x7Hnh 2.25: Mt s hnh dng ch th LCD$2.2 CHUYN I IN T HAY S DNG TRONG O LNG2.2.1 Chun ha tn hiu.a. chun ha v in p0 5V ; 0 5V; 0 10Vb. Chun ha v dng in4 20mA0 20mAS khc nhau gia 4 20mA v 0 20mA th hin trong s ni dy ca thit b o sau: Hnh 2.26.a : chun dng 4 20mA Hnh 2.26.b: chun dng 0 20mA

Thng cc thit b o cn s dng cng sut ln th c ngun cung cp ngoi nh hnh 2.26.b. Khi ng tn hiu v c chun ha v 0 20mA. i vi cc thit b o cng sut thp th s dng tn hiu s cng vi ngun cp, c th hin nh hnh 2.26.a V vy vic chun ha mt tn hiu o l cn thit nhm ghp ni cc thit b vi nhau v nng cao chnh xc ca php o.Trong thc t ngi ta s dng mt vi b chuyn i in t di y chun ha tn hiu o.2.2.2 Mt s b chuyn i in t hay s dng trong o lng.a. B OP.Cc thng s c bn. = == 0>> ;