may hi en song

TRNG I HC LTKHOA VT L B MN IN T VIN THNG

BO CO TIU LUN

MY HIN SNG

Ging vin hng dn:ThS Phan Vn Ngha

Lt, thng 11 nm 2011

Bo co tiu lun my hin sng

Nhm sinh vin thc hin

STT 1 2 3 4 5 6 7 8 9 10 11

H & Tn Hong Th Cc M Th o Hunh Th t Hu L Nguyn T Lm Nguyn Th Kim Lin Hong Th Mai Cao Th i Phng V Minh Phng H Tn Thnh on Th Kim Tho L Th Mai Thi

MSSV 0912775 0912779 0912790 0910348 0912806 0912809 0912830 0910355 0910356 0912849 0912855

A. M U.

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Bo co tiu lun my hin sng Quan st dng sng v o cc tham s ca tn hiu l mt trong nhng yu cu co bn xc nh tn hiu. Cc tn hiu in l nhng hm bin thin theo thi gian, nu thc hin c mt thit b v trc tip th bin thin ca tn hiu theo thi gian th c th quan st hnh dng v o cc tham s ca tn hiu. Thit b cho php quan st dng tn hiu v o c cc tham s gi l my hin sng (oscilloscope). Khi nm chc c cu to, nguyn l lm vic ca my hin sng gip chng ta ng dng hiu qu vo trong thc t. B. NI DUNG I. MY HIN SNG TNG T: 1. S khi tng qut:

Hnh 1: S khi tng qut ca my hin sng tong t. 2. Hot ng: My hin sng bao gm: ng tia cathode (CRT) Cc mch lm lch a) ng tia cathode B phn ch yu ca my hin sng l ng tia in t n thc hin chc nng v dng tn hiu trn my hin sng, v cu to ng tia cathode l mt ng chn khng c v bng thy tinh , bn trong c cc in cc. u ng l hnh tr trn, cha sng in t v hai cp phin lm lch. u cui ca ng loe to thnh hnh dng nn ct, y hnh nn l mn hunh quang, bn trong c qut mt lp than ch dn in.

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Hnh 2: Cu to ng tia cathode V cu to c th coi ng tia in t gm 3 phn c bn: sng in t, b phn lm lch, mn hunh quang. Sng in t bao gm: si t, cathode, li iu khin, cc anode. Sng in t c nhim v to nn mt chm tia in t nh gn v bn ti mn hunh quang gy tc dng pht sng. H thng lm lch gm 2 cp phin mt cp theo phng vung gc gi l cp phin ng Y, mt cp theo phng nm ngang gi l cp phin X, 2 cp phin ny to ra 2 trng tnh in iu khin tia in t theo 2 trc ng v ngang. Mn nh ca n l mt lp hunh quang ph ln lp y ca n. Mu sc v lu nh ph thuc vo cht hunh quang. Chm electron c pht ra t cathode c lm bng vonfram, c t nng gin tip nh si t bng ngun xoay chiu 6,3V pha sau ng chn khng pht x cc in t, cc in t di chuyn qua cc in trng to ra bi cc li hi t v li gia tc, to thanh tia hi t sc nt. Cc chm tia in t nng lng cao s p p vo mn hnh pha trc ng pha trc ng lm cho cc phn t photpho ca ng pht sng. Chm electron phng ra v c iu khin bng cp tia li ngang v cp tia li dc trc khi ti mn hnh quang, chng c t vung gc vi nhau. Nu t trn cp bn lm lch mt hiu in th, th gia chng s tn ti mt in trng. Khi electron bay qua hai bn lm lch s chu tc dng ca lc in trng lm thay i qu o chuyn ng. Chm in t c b cong, c lm lch nu t trn cp bn lm lch mt hiu in th, th gia chng s tn ti mt in trng. Khi electron bay qua hai bn lm lch s chu tc dng ca lc in trng lm thay i qu o chuyn ng. Cc bn cc li theo chiu ngang hay dc s to ra chuyn ng ca chm in t theo phng ngang hay dc tng ng. S lch tia theo chiu ngang c c bng cch s dng tn hiu rng ca. S lm lch tia theo chiu dc c c nh tn hiu cn o.

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b) Lm lch chm tia Lm lch ngang: S lch tia theo chiu ngang c c bng cch s dng tn hiu rng ca. Khi cha c tn hiu t vo phin li X, Y( X: phin li lm lch ngang; Y: phin li lm lch dc) th chm tia in t s p vo gia tm mn hnh trn mn hnh s xut hin mt vt sng trn. c dc hnh dng ca tn hiu dao ng bin thin theo thi gian trn mn hnh ta phi t mt in p qut rng ca trn cp phin lch X. in p qut rng ca l in p c hnh dng bin thin bc nht theo thi gian nh hnh rng ca. iu ny to ra in trng khi in t i qua gia hai phin di tc dng ca in trng th tia in t s thay i qu o chuyn ng dn n qu o ca tia in t s dch chuyn theo phng ngang, sau in p rng ca s tr v li mc 0 nn im sng s tr li im ban u v v nn mt vt sng nm trn mn hnh. B to sng qut rng ca

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Bo co tiu lun my hin sng Hnh 3: B to sng qut ngang Gm 2 khi chnh: b to sng qut rng ca, v trigger schmitt khng o. in p li ra mch to sng qut rng ca a vo li vo trigger schmitt. Mch to sng rng ca hot ng da trn c s s np, x ca t. Q1 v in tr phn cc np cho C1 Q2 x in cho C1 c iu khin bi xung li ra trigger trng thi ban u, th li ra trigger mc bo ha m, in p trn t rt thp, Q2 kha, C1 np, th trn C1 tng, khi in p trn t t ti ngng ca trigger, trigger chuyn sang trng thi bo ha dng, lm Q 2 nhanh chng dn, C1 x qua Q2. Khi th trn C1 gim xung di ngng kch trigger chuyn sang trng thi bo ha m, ri Q2 ngng C1 li np, qu trnh lp i lp li dn n chn C ca Q1 c dng sng rng ca. Lm lch dc Tn hiu cn o s c t ln phin lm lch dc (phin li Y), tng t nh lm lch ngang, do nh hng ca in p lch dc m chm tia in t s b lch theo chiu dc. Nh vy , do tc dng ng thi ca 2 in trng ln 2 cp phin m tia in t dch chuyn c theo phng trc X v phng trc Y. Qu o ca tia in t dch chuyn trn mn hnh s vch ra hnh dng ca tn hiu cn nghin cu bin thin theo thi gian.

Hnh 4: dng sng tn hiu trn mn hnh ca CRT Hnh 3 (a) Dng sng t vo cp phin lch dc (b) Dng sng t vo cp bn lch ngang (c) Dng sng trn mn hnh my hin sng Xa tia qut ngc

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Bo co tiu lun my hin sng Tn hiu rng ca gim rt nhanh t gi tr ln nht v 0, gi l tia quay v hay tia qut ngc. tn hiu qut ngc s khng c nhn thy trn mn hnh, nu khng th dng sng c hin th s tr nn mo dng ln. do trong sut khong thi gian qut ngc, ng tia s gi trng thi ngng pht sng gi l xa tia qut ngc, bng cch cung cp mc in p m cho li iu khin so vi cathode. ng b thu c tn hiu n nh trn my hin sng, cn phi ng b. dng sng trn my hin sng ng yn trn mn hnh th tn hiu cn o = n*chu k tn hiu qut ngang. iu khin bng chc nng Time/Div. 3. My hin sng vt n S khi ca my hin sng vt n (theo kiu qut kch khi). Tn hiu vo thng qua mch suy gim (nh trong voltmeter in t) theo cc thang o khc nhau i vi php o bin . Tn hiu sau s c khuych i bi mch khuych i dc (khuych i - Y), v s c cung cp n cp bn lch dc lm lch theo chiu dc. Mch dao ng qut s to ra tn hiu rng ca v c khuych i cung cp n cp bn lch ngang. Khong thi gian ca tn hiu qut c iu khin bi mch iu khin gc thi gian nn gi tr ca khong thi gian theo vch chia s c ch trn chuyn mch iu khin nh thi trn mt my hin sng. i vi mt s ng dng o (chng hn nh cc mu hnh Lissajous hay cc php o iu ch), cn phi t theo v tr qut ngoi v do vy chuyn mch S2 s cung cp tn hiu qut trong hay qut ngoi n mch khuych i tn hiu qut theo yu cu. gi n nh dng sng hin th, cn phi c cc thi im khi u qut ti cng mt v tr ca chu k tn hiu vo, tc l m b, tn hiu bo s ng vt ngang c to ra bi xung kch khi ly t mch khuych i dc (khuych i - Y) s kch khi mch dao ng qut bng b a hi n n. Khi cn kch khi ngoi, hay kch khi bng tn hiu in ac 50Hz (gn bn trong my hin sng) cng c th s dng bng chuyn mch S1. Dy tr dng b tr gy ra do s khi ng mch qut sau khi kch khi. V vy, dy tr s lm cho tn hiu o v tn hiu qut n cc cp bn lch trong ng tia mt cch ng thi. 4. My hin sng vt kp

Hnh 4: Cu to CRT ca my hin sng vt kp

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Hnh 5: S khi my hin sng hai tia my hin sng vt kp hay hai vt, mt mch qut n s c hin th ti hai v tr dc khc nhau trn mn hnh theo tng chu k rng ca lun phin. S khi my hin sng hai vt nh hnh 5. Chuyn mch in t S3 s chn tn hiu vo dc (Y1), c a n mch khuych i dc (Y) trong mt khong thi gian no , cn tn hiu Y2 s c cung cp n mch khuych i dc trong khong thi gian tip theo. Chuyn mch S1 s cho php kch khi hoc bng tn hiu Y1 hoc bng tn hiu Y2, hay bng tn hiu ngoi, hay kch khi bng tn hiu mng in 50Hz. Cu trc mch nh i vi my hin sng vt n. Chuyn mch t ng c tc nhanh c hai tn hiu c th quan st mt cch r rng trn mn hnh (do lu sng ca cht hunh quang v lu sng vng mc mt). my hin sng hai vt, ch c mt mch qut, nn i vi mt chu k tn hiu qut s iu khin s lm lch dc ca mt dng sng vo, v i vi chu k qut tip theo ca cng mt mch qut, tn hiu qut s iu khin s lm lch dc ca tn hiu vo th hai. Vy hai dng sng ca hai tn hiu vo ring s c hin th, nhng khng c hin th ng thi. Do khng th so snh lch pha gia hai dng sng. so snh quan h v pha, cn phi c hai dng sng c hin th ng thi ti cng thi im, tc l c th thc hin bng my hin sng hai chm tia. 5. Qut lp li Mch qut s nhn c tn hiu lp li theo chi k ca mch dao ng a hi. dng sng n nh, cn phi c s ng b gia tn s qut v tn s ca tn hiu cn o. iu ny c th thc hin bng cch thay i tn s qut nh vic iu khin nh thi.

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Bo co tiu lun my hin sng 6. Qut tr Do xung kch khi, s khi u qut s b tr nn s khng th quan st vt sng trn mn hnh trong khong thi gian no . Tn hiu bn lch dc l lin tc nn mt phn ca tn hiu cn o s b mt. Do cn phi lm tr tn hiu. V tn hiu khng c t trc tip vo cp bn lch dc m phi truyn qua mch dy tr, to ra khong thi gian cn thit cho mch qut khi u ti cp bn lch ngang trc khi tn hiu cn o n cp bn lch dc. Nu tr tn hiu l 200ns, v sng qut b tr khong 80ns, th tn hiu cn quan st s c hin th theo tn hiu qut ng khi bt u qut. 7. My hin sng hai tia My hin sng c thit k vi hao sng in t, hai knh iu khin lch dc v mt knh iu khin lch ngang chung, gi l my hin sng hai tia.

Hnh 6: Cu to my hin sng hai tia S khi my hin sng hai tia

Hnh 7: s khi my hin sng hai tia Nguyn l hot ng: Mi chm tia in t cho mt vt dng sng, mi tia in t c sng in t to ra t cathode qua cc in cc n mng hunh quang c qua cc cp phin lm lch ring ca n (Yxx) dng sng qut rng ca t b gc thi gian a vo cp phin lch ngang v c hai chm tia in t ny c lm lch ngang mt cch ng thi.

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Bo co tiu lun my hin sng 8. Que o L cc u ni my hin sng n cc thit b hay mch in t cn o th cn o th. Mi que o gm hai u d: u d tn hiu vo v u tip t. a) Que o 1:1

Hnh 8: que o 1:1

Cp ng trc c mt in dung tng ng C gi tr c hng trm pF. Tr khng li vo ca my hin sng thng l 1M mc song song vi in dung c 30pF. Tr khng ton phn ca cp ng trc v u vo ca my hin sng phi m bo phi ln hn nhiu so vi tr khng ca ngun tn hiu. Nu iu kin trn khng c tha mn th tn hiu trn b suy gim v b dch pha khi ni vi my hin sng. b) Que o 10:1 C1

Hnh 9: que o 10:1 Mch tng ng nh hnh trn c th c t Cs hoc khng khi khng s dng t Cs th t C1 thay i c. tn hiu n ng vo qut dc gim i 10 ln v khng ph thuc vo tn s tn hiu.

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Bo co tiu lun my hin sng My hin sng s- nh- DSO(digital storage oscilloscope): Trong trng hp cn phi nghin cu nhng tn hiu khng lp li , nhng bin c n. lu gi c dng tn hiu ngi ta s dng cc dao ng k c nh dng s. II.

Hnh 10: My hin sng s 1. S khi

Hnh 11: s khi my hin sng s 2. Hot ng ca my hin sng s

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Bo co tiu lun my hin sng Khi chuyn mch S v tr 1 th OSC lm vic nh 1 OSC a nng thng thng. Khi chuyn mch S t v tr 2 th OSC lm vic l 1 OSC c nh s. in p tn hiu cn quan st c a vo u vo Y, ti b bin i tng t- s ADC. Ti thi im (ti), khi iu khin gi 1 lnh ti u vo iu khin ca b ADC v khi ng qu trnh bin i. kt qu l in p tn hin c s ha, c ngha l b bin i ly mu dng tn hiu nhiu im v bin i gi tr tc thi ca bin ti mi im thnh gi tr m nh phn t l vi bin . Ti thi im kt thc qu trnh bin i, b ADC gi tn hiu kt thc n b iu khin. Mi s nh phn c chuyn ti b nh v c nh v tr nh ring bit. Bi v y l b nh khng linh hot( c nh-nonvolatile memory) nn n c th lu tr lng lu tr ln cc s nh phn vi bt k di thi gian no. Khi cn thit, 1 lnh t khi iu khin c th lm cho cc s nh phn ny c sp xp theo chui li theo th t xc nh v c a ti b bin i DAC. B bin i s-tng t s bin cc gi tr nh phn thnh in p tng ng, v in p ny c a qua b khuch i Y v ti cp phin lm lch Y ca ng tia in t. Do b nh c lin tip qut nhiu ln trong 1s nn mn hnh c sng lin tc v hin ln dng sng l hnh v cc im sng, biu th dng sng cn quan st. t c 1 ng sng lin tc, cn c th thm 1 mch ni suy( lm mt) gia b DAC v b khuch i Y. Mt im hn ch ca DSO va m t trn l di tn b hn ch, do tc ca b bin i ADC thp( thng thng hin nay, DSO c di tn 1-10MHz) 3. u im ca my hin sng s: - Duy tr hnh nh dng ca tn hiu trn mn hnh vi khong thi giankhoong hn ch - Tc c c th thay i trong gii hn rng. - Cc on hnh nh lu gi c th xem li c tc thp hn nhiu, tc qut c th ti 1cm/1h. - To c hnh nh dao dng tt hn, tng phn hn loi OSC tng t. - n gin hn trong s dng v vn hnh. - C th truyn trc tip s liu ca tn hiu cn quan st di dng s, ghp trc tip vi my tnh hay c x l trong OSC. III. Cch s dng v chc nng ca my hin sng 1. Cc phm chc nng iu khin

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Hnh12: Cc phm chc nng iu khin ca my hin sng Power: Cng tc chnh ca my, khi bt cng tc ln th n led s sng Intens: iu chnh m nht cho tia. Focus: iu chnh hi t cho tia. Trigger: iu chnh khi tn hiu b nhiu. AC, DC: Nu DC th s cho bit c thnh phn AC va DC, nu AC ch cho thy thnh phn AC. INTEN: iu chnh sng ca im hoc tia FOCUS: iu chnh sc nt ca hnh TRACE RATOTION: iu chnh tia song song vi ng k ngang trn mn hnh Vertical: CH1: u vo knh 1. CH2: u vo knh 2. AC-GND-DC: Chn la ch ca tn hiu vo v khuch i dc AC ni vi tn hiu xoay chiu GND khuch i dc tn hiu vo c ni t v tn hiu vo c ngt ra DC ni vi tn hiu mt chiu VOLTS/DIV: Chn la nhy ca trc dc t 5mV/DIV n 5V/DIV. Y-POS I: Dng iu chnh v tr ca tia ca knh 1 theo chiu dc. Y-POS II: Dng iu chnh v tr ca tia ca knh 2 theo chiu dc. X-POS: Dng iu chnh v tr ca tia theo chiu ngang. VERT MODE: La chn knh CH1: Ch c 1 knh CH1 CH2: Ch c 1 knh CH2

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Bo co tiu lun my hin sng DUAL: Hin th c hai knh ADD: Thc hin php cng (CH1 + CH2) hoc php tr (CH1-CH2) (php tr ch c tc dng khi CH2 INV c nhn). EXT TRIG IN : u vo Trigger ngoi, s dng u vo ny, ta iu chnh Source v tr EXT SOURCE: Dng chn tn hiu ngun trigger (trong hay ngoi), v tn hiu u vo EXT TRIG IN CH1: Chn Dual hay Add Vert Mode, bn chn CH1 ly tn hiu ngun Trigger trong. CH2: Chn Dual hay Add Vert Mode, chn CH2 ly tn hiu ngun Trigger bn trong. EXT: Chn ngun tn hiu Trigger bn ngoi ti u vo EXT TRIG IN TRIGGER MODE: La chn ch Trigger o Auto: Nu khng c tn hiu Trigger hoc tn hiu Trigger nh hn 25 Hz th mch qut pht ra tn hiu qut t do m khng cn n tn hiu Trigger. o Norm: Khi khng c tn hiu Trigger th mch qut ch ch v khng c tn hiu no c hin th. o TV-V: Dng quan st tn hiu dc ca hnh nh trong TV o TV-H: Dng quan st tn hiu ngang ca hnh nh trong TV Time base: TIME/DIV: Cung cp thi gian qut t 0.2 s/ vch n 0.5 us/vch. X-Y: Dng oscilloscope ch X-Y

SWP.VAR: Nm iu khin thang chy ca thi gian qut c s dng khi CAL v thi gian qut c hiu chnh gi tr t trc ti TIME/DIV. Thi gian qut ca TIME/DIV c th b thay i mt cch lin tc khi trc khng ng v tr 2. Cc bc s dng my hin sng Trc khi bt in, cc nt iu khin chnh sng, nt v tr trung bnh, cc nt chn thang o v tr tn cng bn tri. Cp in cho CRO iu chnh cc nt c mt ng nm ngang gia mn hnh Dng Probe (que o) o tn hiu ti cc im trn mch cn o iu chnh khuch i dc (tc l iu chnh Volt/Div) v tn s qut ngang (tc l iu chnh Time/Div) thu c tn hiu n nh trn mn hnh. 3. Cc php o vi my hin sng

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Bo co tiu lun my hin sng - Quan st dng sng ca tn hiu l php o quan trng nht ca my hin sng T ta c th: - o in p ca tn hiu - o chu k tn hiu bng cch tnh s vch chia ri chia cho s chu k xut hin sau nhn cho gi tr trn nm vch chia. V d: trn thang o 50s/div, c 2 chu k tn hiu chim 4 vch chia, th s vch chia chim bi 1 chu k l 2 vch chia, nn chu k tn hiu l 100s. - o tn s theo mu hnh Liassajous: thc hin bng cch a tn hiu c tn s cn o vo u dc v ni tn hiu c tn s bit vo u vo qut ngoi, s thu c cc mu hnh khc nhau trn mn hnh ty thuc vo t s ca hai tn s v lch pha ca hai tn hiu.

Hnh13: Cc mu hnh Liassajous -o ch s iu ch ca tn hiu AM: Khi tn hiu iu ch c p t lm tn hiu qut ngoi, v tn hiu c iu ch lm tn hiu dc (Y) -o mo xung: Xung vo v xung ra c th c hin th trn my hin sng 2 vt. vng hoc vt qu ca phn nm ngang, v tng hay gim ca cc cnh xung c th quan st trn mn hnh. Thi gian tng (ng vi mc thay i t 10% n 90% bin xung) v khong thi gian gim (ng vi mc thay i t 90% n 10% bin xung) c th o c trn mu xung. rng ca xung s c o trong khong t mc 50% ca cnh tng ln mc 50% ca cnh gim.

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Bo co tiu lun my hin sng 4. ng dng ca my hin sng My hin sng c dng nhiu trong cc lnh vc nh: y khoa, k thut, cng ngh vin thng. Phn tch h thng, v li dng sng, pht hin sai hng. kim tra tn hiu nhm nh gi c trng ca thit b Bo tr thit b in t. 5. Cc im lu khi s dng my hin sng - Ni t v my hin sng. - Cng chm tia in t cn phi gi mc thp c th quan st thun li. im sng khng c lu ti mt v tr trn mn hnh. - Nn bt u php o vi mc nhy nh nht mch khuch i dng v tng dn cho n khi t c mc thit lp thch hp. - nh chun lch dng trc khi thc hin cc php o. C sng ngun in p trong my hin sng cho vic nh chun. - S dng que o ph hp khi thc hin php o trn cc tn hiu tn s cao, hay khi tn hiu vo qu ln. - Khi tho my hin sng sa cha, hy cn thn c in p rt cao khong vi KV. Ngay c trong trng thi ngt chuyn mch ngun in li, cc t lc c in p cao c th gy nguy him cho ngi s dng, do vy t cn phi x khi tin hnh cng vic trn my hin sng trng thi ct ngun. - Phi cn thn khi s dng ng tia, h hng ngu nhin bt k s dn n hng mn hnh. - Mn hnh pht quan c th pht x tia x nh, khi cn thay th nn mua CRT tiu chun t nh sn xut c uy tn. C. TNG KT I. Kt qu t c 1. Hiu c nguyn l hot ng ca cc loi my hin sng. 2. Bit s dng cc phm chc nng ca my hin sng v mt s lu trong qu trnh s dng. 3. Bit cch s dng my hin sng vo cc mc ch khc nhau. 4. Rn luyn k nng thu nht tng hp kin thc, k nng lm vic nhm. II. Cha t c 1. a phn ni dung kin thc l c tng hp t ti liu t cc gio trnh khc nhau, tham kho trn mng Internet, nhm cha thc s ch ng tm ra gii php gii quyt thc mc. 2. Trong qu trnh tm hiu my hin sng cn tn ti nhng vn cha hiu r nh l: ch qut ngoi, mu hnh lisaojus.

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Bo co tiu lun my hin sng D. TI LIU THAM KHO:

I. D Quang Bnh, o lng in t, i hc Bch Khoa Nng, 2000. II. Ths Phan Vn Ngha, Slide o lng in t, i hc Lt, 2011 III. PGS V Qu im, C s k thut o lng in t, NXB khoa hc k thut, 2001IV.

www.wikipedia.org

V. www.dientuvietnam.net

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