Chuong 1

CHNG 1H QUANG IN

KHI NIM CHUNG Bn cht ca h quang in l hin tng phng in trong cht kh vi mt dng in rt ln ( ti khong 102 n 103 A/mm2) c nhit rt cao (ti khong 5000 n 60000C ) v thng km theo hin tng pht sng.

KHI NIM CHUNGH quang in c ch : H quang in thc s c ch khi c s dng trong cc lnh vc nh hn in, luyn thp,...nhng lc ny h quang cn c duy tr chy n nh.

KHI NIM CHUNGH quang in c hi : Khi ng ct cc thit b in nh contct, cu dao, my ct,...h quang s xut hin gia cc cp tip im.H quang chy ny lu sau khi thit b in ng ct s lm h hi cc tip im v bn thn thit b in. Trong trng hp ny m bo lm vic tin cy ca thit b in yu cu phi tin hnh dp tt h quang cng nhanh cng tt.

C TNH H QUANG IN MT CHIU

QU TRNH PHT SINH H QUANG H quang in pht sinh l do mi trng gia cc in cc (hoc gia cc cp tip im) b ion ha (xut hin cc ht dn in). Ion ha c th xy ra bng cc con ng khc nhau dui tc dng ca nh sng, nhit , in trng mnh,.... Trong thc t qu trnh pht sinh h quang in c nhng dng ion ha sau:

QU TRNH PHT SINH H QUANGTrong thc t qu trnh pht sinh h quang in c nhng dng ion ha sau : Qu trnh pht x in t nhit ;Qu trnh t pht x in t ;Qu trnh ion ha do va chm;Qu trnh ion ha do nhit .

S PHT X IN T NHIT in cc v tip im c ch to t kim loi, m trong cu trc kim loi lun lun tn ti cc in t t do chuyn ng v mi hng trong qu o ca cu trc ht nhn nguyn t. Khi tip im bt u m ra lc nn vo tip im gim dn khin in tr tip xc tng ln ch tip xc, dng in b tht li dn n mt dng in tng rt ln lm nng cc in cc (nht l cc m c nhiu electron).

S PHT X IN T NHITKhi b t nng, ng nng ca cc in t tng nhanh n khi nng lng nhn Wn c ln hn cng thot At lin kt ht nhn th in t s thot ra khi b mt cc m tr thnh in t do. Qu trnh ny ph thuc vo nhit in cc, vt liu lm in cc .

S PHT X IN T Khi tip im hay in cc va m ra lc u khong cch cn rt b. Nu c mt in trng ln t ln in cc (nht l vng cc m c khong cch nh c th ti hng triu V/cm), vi cng in trng ln cc m cc in t t do c cung cp thm nng lng s b ko bt ra khi b mt catt tr thnh cc in t t do. Qu trnh ny ph thuc vo cng in trng E v vt liu lm in cc.

ION HA DO VA CHM Sau khi tip im m ra, di tc dng ca nhit cao hoc ca in trng ln (m thng thng l c hai) th cc in t t do s pht sinh chuyn ng t cc dng sang cc m. Do in trng rt ln nn cc in t chuyn ng vi tc rt cao. Trn ng i cc in t ny va chm vi cc nguyn t v phn t kh s lm bt ra cc in t v cc ion dng.

ION HA DO VA CHMCc phn t mang in ny li tip tc tham gia chuyn ng v va chm lm xut hin cc phn t mang in khc.Do vy m s lng cc phn t mang in tng ln khng ngng, lm mt in tch trong khong khng gian gia cc tip im rt ln.Qu trnh ny ph thuc vo cng in trng, mt cc phn t trong vng in cc, lc lin kt phn t, khi lng ca phn t ...

ION HA DO NHIT Do c cc qa trnh pht x in t v ion ha do va chm, mt lng ln nng lng c gii phng lm nhit vng h quang tng cao v thng km theo hin tng pht sng. Nhit kh cng tng th tc chuyn ng ca cc phn t kh cng tng v s ln va chm do cng cng tng ln. Do va chm, mt s phn t kh s phn li thnh cc nguyn t. Cn lng cc ion ha tng ln do va chm khi nhit tng th gi l lng ion ha do nhit.

QU TRNH DP TT H QUANGH quang in s b dp tt khi mi trng gia cc in cc khng cn dn in hay ni cch khc h quang in s tt khi c qu trnh phn ion ha xy ra mnh hn qu trnh ion ha. Ngoi qu trnh phn li ni trn, song song vi qu trnh ion ha cn c cc qu trnh phn ion gm hai hin tng sau: Hin tng ti hpHin tng khuch tn

HIN TNG TI HPTrong qu trnh chuyn ng cc ht mang in tri du va chm nhau, to thnh cc ht trung ha. Trong l thuyt chng minh tc ti hp :T l nghch vi bnh phng ng knh HQH quang tip xc vi mI trng in mi th hin tng ti hp s tng ln. Nhit h quang cng thp tc ti hp cng tng.

HIN TNG KHUCH TN Hin tng cc ht tch in di chuyn t vng c mt in tch cao (vng h quang) ra vng xung quanh c mt in tch thp, lm gim s lng ion trong vng h qung gi l hin tng khuch tn. Cc in t v ion dng khuch tn dc theo thn h quang, in t khuch tn nhanh hn ion dng.

HIN TNG KHUCH TNQu trnh khuch tn c trng bng tc khuch tn. S khuch tn cng nhanh h quang cng nhanh b tt. tng qu trnh khuch tn ngi ta thng tm cch ko di ngn la h quang.

H QUANG IN MT CHIU

H QUANG IN MT CHIU Vi U0 l in p ngun , mch c in tr R, mch c in cm mch L v rhq c trng cho in tr h quang vi in p h quang l uhq trn cc cp tip im khi ta ng hoc ngt.

H QUANG IN MT CHIUTheo nh lut Kichp II, ta c phng trnh cn bng in p trong mch khi m tip im v h quang bt u chy nh sau :

Vi UR : l in p ri trn in tr.Vi Uhq : l in p trn h quang.

H QUANG IN MT CHIUKhi h quang chy n nh th dng in khng i.

Do phng trnh cn bng p s l :

H QUANG IN MT CHIU

IU KIN DP TT H QUANG IN c th dp tt c h quang in mt chiu cn loi b c im h quang chy n nh (im B). Trn c tnh ta nhn thy s khng c im chy n nh khi ng c tnh 3 (in p trn h quang) cao hn ng c tnh 2 nh hnh (tc l h quang s tt khi Uhq> U0- UR)

IU KIN DP TT H QUANG IN nng cao ng c tnh 3 thng thc hin hai bin php l tng di h quang(tng l) v gim nhit vng h quang xung, c tnh nh hnh.

IU KIN DP TT H QUANG IN

QA IN P HQ MT CHIUKhi ct mch in mt chiu thng xy ra qu in p, khi mch c in cm ln nu tc ct cng nhanh th qu in p cng ln. Nu ti thi im ct c I= 0 th :

Hay ta c :

QA IN P HQ MT CHIU l tr s qu in p xoay chiu.Trong mch mt chiu lm vic vi cng sut ln li c nhiu vng dy khi dp h quang in qu in p s xy ra rt ln c th gy nh thng cch in v h hng thit b. hn ch hin tng qu in p ngi ta thng dng thm mt mch in ph mc song song vi ph ti. Mch ny c th l in tr, in tr v t ni tip hoc mt chnh lu mc ngc

QA IN P HQ MT CHIU

H QUANG IN XOAY CHIU

KHI NIM CHUNG h quang in xoay chiu, dng in v in p ngun bin thin tun hon theo tn s li in.V h quang l in tr phi tuyn nn dng in v in p ca h quang trng pha nhau.Ti thi im dng in i qua im 0, h quang khng c cp nng lng nn qu trnh phn ion xy ra vng in cc rt mnh v nu in p t ln 2 in cc b hn tr s in p chy th HQ s tt hn.

KHI NIM CHUNGKhi h quang in xoay chiu ang chy ta a dng in v in p ca h quang vo dao ng k ta s c dng sng ca dng in v in p h quang nh hnh

KHI NIM CHUNGTrong 1/4 chu k u, in p HQ tng nhanh n tri s Uch (theo in p ngun). Khi HQ chy, in p gim dn. Dng in tng t 0 n im chy, dng tng mnh v khi t = T/4, dng in t tr s cc i v in p HQ gn nh khng i. 1/4 chu k tip theo, dng in gim dn, n thi im tt, in p HQ tng sau suy gim v 0 v dng in tr v 0.

KHI NIM CHUNGT dng sng thu c trn mn hnh dao ng k ta xy dng c c tnh Vn -Am pe (V-A) ca h quang in xoay chiu nh hnh I

KHI NIM CHUNGTa nhn thy trong mch c ph ti in tr thun d dp h quang hn trong mch c ti in cm.Bi mch thun tr khi dng in qua tr s khng (thi gian i=0 thc t ko di khong 0,1) th in p ngun cng bng khng (trng pha). Cn mch thun cm khi dng bng khng th in p ngun ang c gi tr cc i (in p vt trc dng in mt gc 900).

DP TT HQ XOAY CHIUH quang in xoay chiu khi dng in qua tr s 0 th khng c cung cp nng lng. Mi trng h quang mt dn tnh dn in v tr thnh cch in. Nu cch in ny ln v in p ngun khng duy tr phng in li th h quang s tt hn. nh gi mc cch in ca in mi vng h quang l ln hay b ngi ta dng khi nim in p chc thng. in p chc thng ( Uch.t ) cng ln th mc cch in ca in mi cng cao.

DP TT HQ XOAY CHIUQu trnh dp tt h quang in xoay chiu khng nhng ty thuc vo tng quan gia ln ca in p chc thng vi ln ca in p h quang m cn ph thuc tng quan gia tc tng ca chng.

BIN PHP V TRANG B DP H QUANG TRONG THIT B IN

CC YU CU DP HQTrong thi gian ngn phi dp tt c h quang, hn ch phm vi chy h quang l nh nht.Tc ng m tip im phi ln.Nng lng h quang sinh ra phi b, in tr h quang phi tng nhanh.Trnh hin tng qu in p khi dp h quang.

CC NGUYN TC DP HQKo di ngn la h quang.Dng nng lng h quang sinh ra t dp.Dng nng lng ngun ngoi dp.Chia h quang thnh nhiu phn ngn dp.Mc thm in tr song song dp.

DP HQ TRONG THIT B H PKo di h quang in bng c khDng cun dy thi t kt hp bung dp h quang Dng bung dp h quang c khe h quanh co Phn chia h quang ra lm nhiu on ngn Tng tc chuyn ng ca tip im ng Kt cu tip im kiu bc cu

DP HQ TRONG THIT B H CAO PDp h quang trong du bin p kt hp phn chia h quang Dp h quang bng kh nn Dp h quang bng cch dng vt liu t sinh kh Dp h quang trong chn khng Dp h quang trong kh p sut cao