MC LC

LI NI U ........................................................................................................ 1

CHNG 1. VN IU KHIN V GIM ST L NHIT ..................... 2

1.1. TNG QUAN V L NHIT IN TR ..................................................... 2

1.1.1. Gii thiu chung v l in tr ..................................................................... 2

1.1.2. Cu to ca l in tr .................................................................................. 2

1.1.3. u nhc im ca l in so vi cc l s dng nhin liu ....................... 3

1.1.5. H thng iu khin l nhit ......................................................................... 5

1.2.CC PHNG PHP O NHIT ........................................................... 6

1.2.1. o nhit bng phng php tip xc ....................................................... 6

1.2.2. o nhit cao bng phng php tip xc................................................. 7

1.2.3. o nhit bng phng php khng tip xc ............................................ 8

1.3. CC LOI CM BIN O NHIT ........................................................ 8

1.3.1. Nhit in tr ................................................................................................ 8

1.3.2. Cm bin cp nhit ngu ............................................................................. 14

1.3.3. Cm bin quang o nhit ....................................................................... 16

1.4. MT S PHNG PHP IU KHIN L NHIT ................................ 20

1.4.1. M t ton hc ca l nhit trong phng th nghim .................................. 20

1.4.2. Phng php iu khin on off ............................................................... 21

1.4.3. Phng php iu khin PID ...................................................................... 23

1.5. GII THIU MT S LOI CM BIN THNG DNG TRONG

CNG NGHIP O NHIT ................................................................... 27

1.5.1. My o nhit siu nh ............................................................................ 27

1.5.2. Thit b o nhit l ................................................................................. 27

1.5.3. Thit b o nhit chuyn nghip P400/P410 .......................................... 28

1.5.4. ng h o nhit .................................................................................... 28

CHNG 2. GII THIU CARD PCI 1710 ...................................................... 29

2.1. CARD PCI-1710 V CC THNG S K THUT ................................. 29

card PCI - 1710 ........................................................... 29

2.1.2. Bus PCI Plug and Play ................................................................................ 29

2.1.3. Nhng kiu u vo v vic thit lp nhng phm vi linh hot ................. 29

2.1.4. Vng nh FIFO trn bng mch (First In First Out) .................................. 29

2.1.5. B m lp trnh c trn bng mch ....................................................... 30

.................................................................................. 31

CHNG 3. XY DNG CHNG TRNH GIM ST NHIT L

NHIT S DNG CARD PCI 1710 ................................................................... 33

3.1. S KHI CA MCH O NHIT ................................................ 34

3.1.1. Khi ngun cp ........................................................................................... 34

3.1.2. Khi ngun dng ......................................................................................... 34

3.1.3. Khi khuch i .......................................................................................... 36

3.1.4. Khi PCI-1710 ............................................................................................ 36

3.2. S NGUYN L .................................................................................... 36

3.2.1. Mch ngun dng ........................................................................................ 36

3.2.2. Mch khuch i ......................................................................................... 37

3.2.3. Mch iu khin .......................................................................................... 38

3.2.4. Mch ng lc ............................................................................................. 41

3.2. GIAO TIP PHN MM MATLAB VI CARD PCI-1710 ....................... 43

3.3. THUT TON .............................................................................................. 51

3.4. GIAO DIN CHNG TRNH GIM ST ............................................... 52

3.4.1. M hnh l nhit trn simulink .................................................................... 52

3.4.2. Giao din chng trnh ............................................................................... 58

KT LUN ........................................................................................................... 60

TI KIU THAM KHO .................................................................................... 61

1

LI NI U

Trong nhiu lnh vc sn xut cng nghip hin nay, nht l ngnh

cng nghip luyn kim, ch bin thc phmVn o v khng ch nhit

c bit c ch trng n v n l mt yu t quyt nh n cht lng

ca sn phm. Nm c tm quan trng ca vn trn em chn ti

tt nghip:

Nghin cu vn iu khin l nhit. i su xy dng chng trnh

gim st nhit l nhit trong phng th nghim s dng card PCI 1710.

n ca em c trnh by trong 3 chng:

Chng 1. Vn iu khin v gim st l nhit

Chng 2. Gii thiu v card PCI 1710

Chng 3. Xy dng chng trnh gim st nhit l nhit s dng

card PCI 1710

Mc d em rt c gng hon thnh n ca mnh nhng khng

th trnh khi nhng thiu st em mong thy c cng cc bn ng gp

kin em c th hon thin ti ca mnh hn.

Sinh vin thc hin

Bi V Cng

2

CHNG 1. VN IU KHIN V GIM ST L

NHIT

1.1. TNG QUAN V L NHIT IN TR

1.1.1. Gii thiu chung v l in tr

L in l mt thit b in bin in nng thnh nhit nng dng trong

cc qu trnh cng ngh khc nhau nh nung hoc nu luyn cc vt liu, cc

kim loi v cc hp kim khc nhau v.v...

L in c s dng rng ri trong cc lnh vc k thut :

+ Sn xut thp cht lng cao

+ Sn xut cc hp kim phe-r

+ Nhit luyn v ho nhit luyn

+ Nung cc vt phm trc khi cn, rn dp, ko si

+ Sn xut c v kim loi bt

Trong cc lnh vc cng nghip khc :

+ Trong cng nghip nh v thc phm, l in c dng sy,

m vt phm v chun b thc phm

+ Trong cc lnh vc khc, l in c dng sn xut cc vt

phm thu tinh, gm s, cc loi vt liu chu la v.v...

L in khng nhng c mt trong cc ngnh cng nghip m ngy cng

c dng ph bin trong i sng sinh hot hng ngy ca con ngi mt

cch phong ph v a dng: Bp in, ni nu cm in, bnh un nc in,

thit b nung rn, sy in v.v...

1.1.2. Cu to ca l in tr

L in tr thng gm 3 phn chnh l: v l, lp lt v dy nung.

a. V l

3

V l in tr l mt khung cng vng, ch yu chu trng ti trong qu

trnh lm vic ca l. Mt khc v l cng dng gi lp cch nhit v m

bo s kn ca l.

i vi cc l lm vic vi kh bo v cn thit v l phi hon ton kn,

cn i vi cc l in tr bnh thng , s kn ca v l ch cn gim tn

tht nhit v trnh s la ca khng kh lnh vo l.

Khung v l cn lm cng vng chu trng ti ca lp lt, ph ti l

v cc c cu c kh gn trn v l.

b. Lp lt

Lp lt l in tr thng gm 2 phn vt liu chu la v cch nhit.

Phn vt liu chu la c th xy bng gch tiu chun, gch hnh hoc

gch hnh c bit ty theo hnh dng kch thc ca bung l. Cng c khi

ngi ta m bng cc loi bt chu la v cc cht kt dnh gi l cc khi

m. Khi m c th tin hnh ngay trong l v cng c th tin hnh ngoi

nh cc khun.

Phn cch nhit thng nm gia v l v phn chu la. Mc ch ch

yu ca phn ny l gim tn tht nhit. Ring i vi y phn cch nhit

i hi phi c bn c hc nht nh. Phn cch nhit c th xy bng gch

cch nhit hoc cc lp cch nhit.

c. Dy nung

Dy nung l b phn pht nhit ca l, lm vic trong nhng iu kin

khc nhit do phi m bo c cc yu cu cn thit.Theo c tnh ca

vt liu dng lm dy nung ngi ta chia dy nung lm 2 loi: dy nung kim

loi v dy nung phi kim loi. m bo yu cu ca dy nung trong hu

ht cc l in tr cng nghip, dy nung kim loi c ch to bng hp kim

Crm Nhm v Crm Niken l hp kim c in tr sut ln.

1.1.3. u nhc im ca l in so vi cc l s dng nhin liu

a. u im

4

+ C kh nng to c nhit cao

+ m bo tc nung ln v nng sut cao

+ m bo nung u v chnh xc do d iu chnh ch in v

nhit

+ Kn

+ C kh nng c kh ho v t ng ho qu trnh cht d nguyn

liu v vn chuyn vt phm.

b. Nhc im

+ Nng lng in t

+ Yu cu c trnh cao khi s dng.

1.1.4. Nguyn l lm vic ca l in tr

L in tr lm vic da trn c s khi c mt dng in chy qua mt

dy dn hoc vt dn th s to ra mt lng nhit theo nh lut Jun-

Lenx[8]:

2. . (1.1)Q I R t

Q - Lng nhit tnh bng Jun (J)

I - Dng in tnh bng Ampe (A)

R - in tr tnh bng ( )

t - Thi gian tnh bng giy (s)

T cng thc trn ta thy in tr R c th ng vai tr :

+ Vt nung: Trng hp ny gi l nung trc tip

+ Dy nung: Khi dy nung c nung nng n s truyn nhit cho

vt nung bng bc x, i lu, dn nhit hoc phc hp. Trng hp ny gi

l nung gin tip.Trng hp th nht t gp v n ch dng nung nhng

vt c hnh dng n gin ( tit din ch nht, vung v trn ).

5

Trng hp th hai thng gp nhiu trong thc t cng nghip. Cho nn

ni n l in tr khng th khng cp n vt liu lm dy nung, b

phn pht nhit ca l.

1.1.5. H thng iu khin l nhit

Nhit l mt i lng vt l,n hin din khp ni c trong sn

xut ln sinh hot hng ngy. Qu trnh o v kim sot nhit trong sn

xut cng nghip ng vai tr to ln trong h thng iu khin t ng, gp

phn quyt nh cht lng sn phm.Khi thu thp d liu cho qu trnh iu

khin v gim st trong nh my th nhit l mt thng s khng th b

qua.

Ty theo yu cu v tnh cht ca qu trnh iu khin m ta s dng

phng php iu khin thch hp.Tnh chnh xc v n nh nhit cng

t ra vn cn gii quyt.

H thng iu khin nhit thng c chia lm hai loi:

+ H thng iu khin hi tip (feedback control system): thng

xc nh v gim st kt qu iu khin,so snh vi tn hiu t v t ng

iu chnh li cho ng.

+ H thng iu khin tun t (sequence control system): thc hin

tng bc iu khin ty theo hot ng iu khin trc khi xc nh tun

t.

Mt h thng mun t c chnh xc cn thit cn thit phi thc

hin hi tip, tn hiu phn hi v so snh vi tn hiu vo v sai lch s c

a ti b iu chnh u ra. H thng iu khin ny c nhiu u im c

s dng nhiu trn thc t trong cc h thng iu khin t ng. Dng tng

qut ca h thng iu khin c m t trn nguyn tc nh hnh sau[4]:

6

Hnh 1.1. Nguyn tc iu khin hi tip

1.2. CC PHNG PHP O NHIT

Nhit l mt trong nhng thng s quan trng nht nh hng n c

tnh ca vt cht nn trong cc qu trnh k thut cng nh trong i sng

hng ngy rt hay gp yu cu o nhit . Ngy nay hu ht cc qu trnh

sn xut cng nghip, cc nh my u c yu cu o nhit .

Ty theo nhit o c th dng cc phng php khc nhau, thng

phn loi cc phng php da vo di nhit cn o. Thng thng nhit

o c chia thnh ba di: nhit thp, nhit trung bnh v cao.

nhit trung bnh v thp: phng php thng o l phng php

tip xc ngha l cc chuyn i c t trc tip ngay mi trng cn o.

i vi nhit cao: o bng phng php khng tip xc, dng c t

ngoi mi trng o.

1.2.1. o nhit bng phng php tip xc

Phng php o nhit trong cng nghip thng c s dng l cc

nhit k tip xc. C hai loi nhit k tip xc, gm: nhit k nhit in tr v

nhit k nhit ngu .

Ngoi ra i vi cc ng dng n gin, di nhit c -5500 C 20000

C hin nay ngi ta thng ng dng cc IC bn dn ng dng tnh cht nhy

nhit ca cc it, tranzito o nhit .

7

Cu to ca nhit k nhit in tr v cp nhit ngu cng nh cch lp

ghp chng phi m bo tnh cht trao i nhit tt gia chuyn i vi mi

trng o:

+ i vi mi trng kh v nc: chuyn i c t theo hng

ngc li vi dng chy.

+ Vi vt rn kh: t nhit k st vo vt, nhit lng s truyn t vt

sang chuyn i v d gy tn hao vt, nht l vi vt dn nhit km. Do vy

in tip xc gia vt o v nhit k cng ln cng tt.

+ Khi o nhit ca cc cht dng ht (ct, t...): cn phi cm su

nhit k vo mi trng cn o v thng dng nhit in tr c cp ni ra

ngoi.

1.2.2. o nhit cao bng phng php tip xc

mi trng nhit cao t 1600 0C tr ln, cc cp nhit ngu khng

chu c lu di, v vy o nhit cc mi trng ngi ta da trn

hin tng qu trnh qu t nng ca cp nhit. Qu trnh qu khi t

nng cp nhit c phng trnh[8]:

( ) .(1 ) (1.2) t

f t T e

Trong : : Lng tng nhit ca u nng trong thi gian t.

T: Hiu nhit ca mi trng o v cp nhit.

: Hng s thi gian ca cp nhit ngu.

Da trn quan h ny c th xc nh c nhit ca i tng o m

khng cn nhit u cng tc ca cp nhit ngu phi t n nhit y.

Bng cch nhng nhit ngu vo mi trng cn o trong khong 0,4 0,6 s

ta s c phn u ca c tnh qu trnh qu ca nhit ngu v theo

tnh c nhit ca mi trng.

8

Nu nhit u cng tc ca cp nhit ngu trong thi gian nhng vo

mi trng cn o t nhit vo khong mt na nhit mi trng th

nhit tnh c c sai s khng qu hai ln sai s ca nhit k nhit ngu

o trc tip. Phng php ny thng dng o nhit ca thp nu chy.

1.2.3. o nhit bng phng php khng tip xc

y l phng php da trn nh lut bc x ca vt en tuyt i, tc

l vt hp th nng lng theo mi hng vi kh nng ln nht. Bc x nhit

ca mi vt th c trng bng mt ph E ngha l s nng lng bc x

trong mt dn v thi gian vi mt n v din tch ca vt xy ra trn mt

n v ca di sng. Quan h gia mt ph bc x ca vt en tuyt i

vi nhit v di sng c biu din bng cng thc [8]:

2/( )0 5 1

1 ( 1) (1.3)C TE C e

Trong : C1, C2 hng s, - di sng, T nhit tuyt i.

C1=37,03.10-17

Jm2/s; C2=1,432.10

-2 m..

1.3. CC LOI CM BIN O NHIT

1.3.1. Nhit in tr

Nguyn l hot ng ca cc loi nhit in tr ch yu l da trn s

thay i gi tr in tr ca cc loi vt liu dn in v bn dn khi c s

thay i nhit ca chng. Chnh v vy m ngi ta s dng nhit in tr

lm phn t cm bin nhit ; tuy nhin ty theo yu cu s dng m ngi

ta c th dng nhit in tr kim loi hoc nhit in tr bn dn[8].

a. Nhit in tr kim loi

i vi nhit in tr kim loi th vic ch to n thch hp hn c l s

dng cc kim loi nguyn cht nh: platin, ng, niken. tng nhy cm

nn s dng cc kim loi c h s nhit in tr cng ln cng tt. Tuy nhin

9

ty thuc vo khong nhit cn kim tra m ta c th s dng nhit in

tr loi ny hay khc. C th: nhit in tr ch to t dy dn bng ng

thng lm vic trong khong nhit t -500 1500C vi h s nhit in

tr =4,27.10-3; Nhit in tr t dy dn platin mnh lm vic trong khong

nhit -1900 6500C vi =3,968.10-3 C

0

1; Nhng khi lm vic ngn

hn, cng nh khi t in tr nhit trong chn khng hoc kh trung tnh th

nhit lm vic ln nht ca n c th cn cao hn.

Cu trc ca nhit in tr kim loi bao gm: dy dn mnh kp i

qun trn khung cch in to thnh phn t nhy cm, n c t trong

chic v c bit c cc cc a ra. Gi tr in tr nhit c ch to t

10 100 .

i vi nhit in tr kim loi th quan h gia in tr vi nhit c

dng sau[8]:

R( ) = R0(1+ . + . 2+ .

3+...) (1.4)

Trong : R0 -in tr dy dn ng vi nhit ban u 00C.

R -in tr dy dn ng vi nhit .

-nhit [0C]

, , -cc h s nhit in tr = const. C

0

1

thy r hn na v bn cht ca nhit in tr kim loi, chng ta c

th xem qua in tr sut ca n c tnh theo cng thc[8] :

1

n.e. (1.5)

10

Trong : n- -s in t t do trong mt n v th tch.

e -in tch ca in t t do.

- -tnh linh hot ca in t, c c trng bi tc ca

trong trng c cng 1vn/cm.

Cc kim loi dng lm in tr nhit thng c in tr sut nh

10-5

10-6

/cm, v c mt in t ln (khng ph thuc vo nhit ).

Khi nhit tng ph thuc vo s dao ng ca mng tinh th kim loi,

tc l n c xc nh bi tnh linh hot ca cc in t. Nh vy khi c s

thay i nhit th cng lm cho tnh linh hot ca cc in t thay i theo.

Tuy nhin tnh linh hot ca cc in t cn ph thuc vo mt tp cht

trong kim loi. C th in tr sut ca kim loi nguyn cht c th xc nh

theo dng: = 0 + ( ), trong 0 khng ph thuc vo nhit ; cn ( )

l mt hm ph thuc khng c nh: ng vi nhit trong khong no

th n l tuyn tnh ( ) = K. , nhng ng vi nhit rt thp ( 00C) th

quan h l hm bc nm ca nhit . Trn hnh 1.2.a biu din mi quan

Hnh1.2. c tnh nhit (a) v c tnh vn_ampe

ca nhit in tr kim loi (b).

ng

platin

R

10

5

0 20 40 60 K

U

I

0

a) b)

11

h gia in tr v nhit , hnh 1.2.b l dng c tnh vn-ampe ca nhit

in tr kim loi.

nhy cm ca nhit in tr c xc nh theo biu thc[8]:

R

d

dRS (1.6)

Trong : R -s thay i in tr khi c s thay i nhit . Vic

s dng nhit in tr kim loi o nhit cao rt tin cy, m bo

chnh xc cao n 0,0010C v sai s o khng qu 0,5 n 1%; Tuy nhin khi

dng ti qua n c gi tr khng ln lm. Nu nh c dng in ln lun

chy qua nhit in tr, th s qu nhit ca n s ln hn rt nhiu so vi

mi trng xung quanh. Khi qu nhit xc lp s c xc nh bi

iu kin truyn nhit trn b mt ca nhit in tr (tc chuyn ng ca

mi trng cn kim tra so vi nhit in tr, v t trng ca mi trng ).

Hin tng ny c s dng o tc thng lng (dng chy) ca cht

lng v kh, cng nh o t trng ca kh.... Bn cnh u im trn th bn

thn nhit in tr kim loi c nhng nhc im sau:

Th nht n l khu phi chu k c m t bng phng trnh vi phn

bc nht n gin:

(TP+1)R(t) = K (t) (1.7)

Trong hng s thi gian T ca n c gi tr t vi giy n vi trm

giy. K chnh l nhy S.

Th hai rt c bn l kch thc ca nhit in tr kim loi ln nn

hn ch vic s dng n o nhit ni hp.

12

b. Nhit in tr bn dn

Nhit in tr c ch to t vt liu bn dn c gi l termistor;

Chng c s dng rng ri trong cc h thng t ng kim tra v iu

khin. Termistor c ch to t hp kim ca ng - mng gan hoc c ban -

mng gan di dng thi, a trn hoc hnh cu. Loi ny hon ton tri

ngc vi nhit in tr kim loi: khi nhit tng th in tr ca n li

gim theo quy lut[8]:

R( ) = R0.e-

= R0(1- + 2

2

2

- ...) (1.8)

Trong h s nhit in tr ca termistor thng c gi tr

= (0,03 0,06). C

0

1

in tr sut ca termistor c tnh theo cng thc[8]:

= A.e B/

(1.9)

Trong : A -hng s ph thuc kch thc ca termistor

B -hng s ph thuc tp cht trong cht bn dn

13

Cng nh in tr nhit kim loi, termistor cng c hai c tnh: c tnh

nhit l quan h gia in tr ca termistor vi nhit (hnh 1.3.a) v c

tnh vn - ampe l quan h gia in p t trn termistor vi dng in chy

qua n ng vi nhit no 0 (hnh 1.3.b). Chng ta thy rng c tnh

vn - ampe ca termistor c gi tr cc i ca U ng vi I1 no , l do khi

tng dng ln hn I1 th n s nung nng termistor v lm cho gi tr in tr

ca n gim xung.

Cc loi termistor thng c ch

to t vi chc n vi chc K .

Termistor c in tr ln cho php t n

v tr cn kim tra kh xa so vi ni b tr h

thng o lng. Chng c th lm vic trong

khong nhit t 600C n +1800C, v

cho php o nhit vi chnh xc

0,00050C. s dng termistor nhit

ln hn, hoc nh hn khong nhit lm

vic bnh thng th ngi ta phi s dng

n cc t hp cht bn dn khc. So vi in tr nhit kim loi th termistor

c kch thc v trng lng nh hn, do cho php chng ta t n

nhng ni cht hp kim tra nhit ca i tng no [8].

Hnh 1.5. S mch cu hai dy nhit k nhit in tr

+

E

_

R

1 R

2

R3

UR

RT

U I

R

V

Hnh 1.4. S cu in tr o nhit

14

gim sai s do nhit mi trng thay i ngi ta s dng cu ba

dy nh hnh sau[8]:

Hnh 1.6. S mch cu ba dy nhit k nhit in tr

Trong s ny hai dy mc vo cc nhnh k ca mch cu, dy th 3

mc vo ngun cung cp. Khi cu lm vic ch cn bng v nu R2=R4

; Rd1=Rd2 sai s do s thay i in tr ca ng dy s c loi tr. Khi

cu lm vic ch khng cn bng sai s gim ng k so vi cu hai

dy. Thc cht khi cu lm vic ch khng cn bng sai s ch yu do s

thay

i in p ca ngun cung cp gy nn.

1.3.2. Cm bin cp nhit ngu

Phng php o nhit bng cp nhit ngu l mt trong nhng

phng

php ph bin v thun li nht.

Cu to ca nhit k cp nhit ngu nh hnh 1.4[8]:

Hnh 1.7. Cu to ca nhit k cp nhit ngu

15

1: v bo v; 2: mi hn; 3: dy in cc; 4: s cch

in;

5: b phn lp t; 6: vt ni dy; 7: dy ni; 8: u ni

dy;

u lm vic ca cc in cc (3) c hn vi nhau bng hn kh

hoc bng tia in t. u t do ni vi dy (7) ti dng c o nh cc vt (6)

t trong u ni dy (8). cch ly cc in cc ngi ta s dng ng s

cch in (4), s cch in phi tr v mt ha hc v bn c v nhit

khi lm vic nhit lm vic. m bo cho cc in cc ta dng v bo

v (1) lm bng s chu nhit hoc bng thp chu nhit.

B cm bin cp nhit ngu l mt mch c t hai hay nhiu thanh dn

in gm hai dy dn A v B. Ch ni gia hai thanh kim loi ny c hn

vi nhau. Nu nhit cc mi hn t v t0 khc nhau th trong mch khp kn

c mt dng in chy qua. Chiu ca dng nhit in ny ph thuc vo

nhit tung ng ca mi hn, ngha l t > t0 th dng in chy theo hng

A B

2

1

t

t0

A B

C

t0 t0

1

2 3

Hnh 1.8. a) S cp nhit ngu, b) S ni cp nhit ngu

16

ngc li. Nu h mt u th gia hai cc xut hin mt sc in ng

(s) nhit. Nh vy bng cch o sc in ng ta c th tm c nhit t

ca i tng o vi t0 = const.

Cch u dng c o vo mch b bin i nhit in trn hnh 1.8b.

1.3.3. Cm bin quang o nhit

Tt c cc vt th c nhit ln hn nhit tuyt i u pht ra cc

bc x nhit. Dng c o nhit vt th bng bc x nhit c gi l ho

k bc x hay mt cch n gin l ho k.

Bc x nhit l cc bc x in t to ra cc cht do ni nng ca

chng (vi bc x hunh quang do kch thch ca ngun ngoi). Ta nhn thy

rng cng bc x nhit gim mnh khi nhit ca vt gim.

Ho k c dng ch yu o nhit t 300 - 60000 C v cao hn.

o nhit n 30000 C phng php duy nht l dng ho k v n

khng phi tip xc vi mi trng o. Ta nhn thy vi phng php o

khng tip xc c tnh u vit l khng lm sai lch nhit ca i tng o.

a. Ho quang k pht x

Nguyn l hot ng: i vi vt en tuyt i, nng lng bc x ton

phn

trn mt n v b mt c tnh[8]:

0 4. (1.10) T pE T

Vi: = 4,96 .10-2 J/m2.s.grad4

Tp: Nhit ca vt theo l thuyt.

i vi vt thc th nng lng bc x ton phn trn mt n v b

mt c

tnh:

17

4. . (1.11) T T tE T

Vi: T: H s bc x tng hp, xc nh tnh cht ca vt v nhit

ca n (T < 1)

Tt: Nhit thc ca vt.

Ho quang k pht x c khc theo bc x ca vt en tuyt i

nhng khi o i tng thc, TP c tnh theo cng thc:

4 4

4

. . . (1.12)

1.

(1.13)

p T t

t p

T

T T

T T

Hnh 1.9. Cu to ca ha quang k pht x

Cu to: Bao gm ng kim loi mng (1), nhit in tr (2) t trong hp

chn (4), gng lm (3), cc ng rnh (5), tm thy tinh hu c (6).

Chm tia pht x c gng lm phn x hi t trn nhit in tr (2) v

t nng n. trnh cc tia phn x t thnh ng bn trong v nhit in tr

ngi

ta gia cng thm nhng ng rnh (5). Nhit in tr c t trong hp

chn (4). bo v mt trong ca ho quang k phi sch, pha u ng c

gn tm knh thu tinh hu c trong sut (6).

18

Nhit in tr c mc vo mt nhnh cu t cn bng cung cp t

ngun

in xoay chiu tn s 50Hz.

c im: Ha quang k dng o nhit t (20 1000C). Khi cn

o nhit

cao hn (100 25000C) m tn s bc sng ln ngi ta dng mt

thu

knh bng thch anh hay thy tinh c bit tp trung cc tia pht x v

phn t nhy cm vi nhit c thay bng cp nhit ngu (v d crmel

- copel).

Nhc im ca tt c cc loi ho quang k pht x l i tng o

khng

phi l vt en tuyt i do trong vt nng c s pht x ni ti v dng

pht

x nhit i qua b mt. Nhit ca i tng o khi dng ho quang k pht

x

Tt bao gi cng nh hn nhit l thuyt tnh ton Tp, v d i vi thp s

khc nhau gia Tp v Tt t n 1,7 C.

b. Ho quang k mu sc

Nguyn l hot ng: ho quang k mu sc l dng c o nhit da

trn

phng php o t s cng bc x ca hai nh sng c bc sng khc

nhau

1 v 2.

Nng lng thu c[8]:

2 2

1 25 5

1 1 1 1 2 2 1 2 (1.14) ;

c c

T TE C e E C e

Ta rt ra c: