gt cam bien dien cong nghiep
TRANSCRIPT
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
1/179
****************************************************************i hc nng
Trng i hc bch khoa-----------------------------------
Th.S. Hong Minh Cng
Gio trnh
Cm bin cng nghip
- Nng 2004 -****************************************************************
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
2/179
Li mu
Cm bin c nh ngha nh mt thit b dng cm nhn v bin i cc
i lng vt l v cc i lng khng mang tnh cht in thnh cc i lng in
c tho c. N l thnh phn quan trng trong mt thit bo hay trong mt hiu khin tng.
t lu cc b cm bin c s dng nh nhng b phn cm nhn v
pht hin, nhng ch t vi ba chc nm tr li y chng mi th hin vai tr quan
trng trong k thut v cng nghip c bit l trong lnh vc o lng, kim tra v
iu khin tng. Nhcc tin b ca khoa hc v cng ngh trong lnh vc vt liu,
thit bin t v tin hc, cc cm bin c gim thiu kch thc, ci thin tnh
nng v ngy cng mrng phm vi ng dng. Giy khng c mt lnh vc no m khng s dng cm bin. Chng c mt trong cc h thng tng phc tp,
ngi my, kim tra cht lng sn phm, tit kim nng lng, chng nhim mi
trng. Cm bin cng c ng dng rng ri trong lnh vc giao thng vn ti, sn
xut hng tiu dng, bo qun thc phm, sn xut t ... Bi vy trang b nhng kin
thc cbn v cm bin trthnh mt yu cu quan trng i vi cc cn b k thut.
i vi sinh vin ngnh cin t cng nh cc ngnh tng ho trong cc
trng i hc k thut, mn hc cm bin cng nghip l mt mn hc bt buc trong
chng trnh o to, nhm trang b nhng kin thc cbn v cm bin hc tt
cc mn hc chuyn ngnh. Gio trnh cm bin cng nghip c vit cho chuyn
ngnh cin t gm 10 chng, gii thiu nhng kin thc cbn v cm bin, cu
to, nguyn l hot ng, cc c trng cbn v s mch o ca nhng cm bin
c s dng ph bin trong cng nghip cng nh trong th nghim, nghin cu v
c sp xp theo cng dng ca cc b cm bin.
Do ni dung gio trnh bao qut rng, ti liu tham kho hn ch v trnh c
hn ca ngi bin son nn chc chn gio trnh khng trnh khi sai st. Tc gi
mong mun nhn c s gp ca bn c v ng nghip gio trnh c hon
thin hn. Cc nhn xt, gp xin gi v Khoa Ckh Trng i hc Bch Khoa,
i hc Nng.
Tc gi
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
3/179
Chng I
Cc Khi nim v c trng cbn
1.1. Khi nim v phn loi cm bin
1.1.1. Khi nim
Cm bin l thit b dng cm nhn bin i cc i lng vt l v cc i
lng khng c tnh cht in cn o thnh cc i lng in c tho v x l
c.
Cc i lng cn o (m) thng khng c tnh cht in (nh nhit , p sut
...) tc ng ln cm bin cho ta mt c trng (s) mang tnh cht in (nhin tch,
in p, dng in hoc trkhng) cha ng thng tin cho php xc nh gi tr ca
i lng o. c trng (s) l hm ca i lng cn o (m):
( )mFs =
(1.1)
Ngi ta gi (s) l i lng u ra hoc l phn ng ca cm bin, (m) l i
lng u vo hay kch thch (c ngun gc l i lng cn o). Thng qua o c (s)
cho php nhn bit gi tr ca (m).
1.1.2. Phn loi cm bin
Cc b cm bin c phn loi theo cc c trng cbn sau y:
- Theo nguyn l chuyn i gia p ng v kch thch (bng 1.1).Bng 1.1
Hin tng Chuyn i p ng v kch thch
Hin tng vt l
- Nhit in
- Quang in
- Quang t
- in t
- Quang n hi
- Tin- Nhit t...
Ho hc
- Bin i ho hc
- Bin i in ho
- Phn tch ph ...
- Bin i sinh ho
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
4/179
Sinh hc - Bin i vt l
- Hiu ng trn cth sng ...
- Phn loi theo dng kch thch (bng 1.2)
Bng 1.2
m thanh
- Bin pha, phn cc
- Ph
- Tc truyn sng ...
in
- in tch, dng in
- in th, in p
- in trng (bin, pha, phn cc, ph)
- in dn, hng sin mi ...
T
- T trng (bin, pha, phn cc, ph)
- T thng, cng t trng
- t thm ...
Quang
- Bin, pha, phn cc, ph
- Tc truyn
- H s pht x, khc x
- H s hp th, h s bc x ...
C
- V tr
- Lc, p sut
- Gia tc, vn tc- ng sut, cng
- M men
- Khi lng, t trng
- Vn tc cht lu, nht ...
Nhit
- Nhit
- Thng lng
- Nhit dung, t nhit ...
Bc x- Kiu- Nng lng
- Cng ...
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
5/179
- Theo tnh nng ca b cm bin (bng 1.3)
Bng 1.3
- nhy
- chnh xc
- phn gii
- chn lc
- tuyn tnh
- Cng sut tiu th
- Di tn
- tr
- Kh nng qu ti
- Tc p ng
- n nh
- Tui th
- iu kin mi trng
- Kch thc, trng lng
- Phn loi theo phm vi s dng ( bng 1.4).
Bng 1.4
- Cng nghip
- Nghin cu khoa hc
- Mi trng, kh tng
- Thng tin, vin thng
- Nng nghip
- Dn dng
- Giao thng
- V tr
- Qun s
- Phn loi theo thng s ca m hnh mch thay th :
+ Cm bin tch cc c u ra l ngun p hoc ngun dng.
+ Cm bin thng c c trng bng cc thng s R, L, C, M .... tuyn tnh hoc
phi tuyn.
1.2. ng cong chun ca cm bin1.2.1. Khi nim
ng cong chun cm bin l ng cong biu din s ph thuc ca i lng in
(s) u ra ca cm bin vo gi tr ca i lng o (m) u vo. ng cong chun c
th biu din bng biu thc i s di dng ( )mFs = , hoc bng th nh hnh 1.1a.
s
si
s
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
6/179
Da vo ng cong chun ca cm bin, ta c th xc nh gi tr mi cha bit ca m
thng qua gi tro c si ca s.
d s dng, ngi ta thng ch to cm bin c s ph thuc tuyn tnh gia
i lng u ra v i lng u vo, phng trnh s= F(m) c dng s = am +b vi a,
b l cc h s, khi ng cong chun l ng thng (hnh 1.1b).
1.2.2. Phng php chun cm bin
Chun cm bin l php o nhm mc ch xc lp mi quan h gia gi tr s o
c ca i lng in u ra v gi tr m ca i lng o c tnh n cc yu t
nh hng, trn cs xy dng ng cong chun di dng tng minh ( th
hoc biu thc i s). Khi chun cm bin, vi mt lot gi tr bit chnh xc mi
ca m, o gi tr tng ng si ca s v dng ng cong chun.
a) Chun n gin
Trong trng hp i lng o ch c mt i lng vt l duy nht tc ng ln
mt i lng o xc nh v cm bin s dng khng nhy vi tc ng ca cc i
lng nh hng, ngi ta dng phng php chun n gin. Thc cht ca chun
n gin l o cc gi tr ca i lng u ra ng vi cc gi xc nh khng i ca
i lng o u vo. Vic chun c tin hnh theo hai cch:
m1 m2
s1
s2
s
m
Hnh 1.2 Ph ng php chu n c m bi n
Hnh 1.1 ng cong chu n c m bi na) D ng ng cong chu n b) ng cong chu n c a c m bi n tuy n tnh
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
7/179
- Chun trc tip: cc gi tr khc nhau ca i lng o ly t cc mu chunhoc cc phn t so snh c gi tr bit trc vi chnh xc cao.
- Chun gin tip: kt hp cm bin cn chun vi mt cm bin so snh csn ng cong chun, c hai c t trong cng iu kin lm vic. Khi tc ng ln
hai cm bin vi cng mt gi tr ca i lng o ta nhn c gi tr tng ng ca
cm bin so snh v cm bin cn chun. Lp li tng t vi cc gi tr khc ca i
lng o cho php ta xy dng c ng cong chun ca cm bin cn chun.
b) Chun nhiu ln
Khi cm bin c phn t b tr (tr choc tr t), gi tro c u ra ph
thuc khng nhng vo gi tr tc thi ca i lng cn o u vo m cn ph
thuc vo gi tr trc ca ca i lng ny. Trong trng hp nh vy, ngi ta
p dng phng php chun nhiu ln v tin hnh nh sau:
- t li im 0 ca cm bin: i lng cn o v i lng u ra c gi trtng ng vi im gc, m=0 v s=0.
- o gi tru ra theo mt lot gi tr tng dn n gi tr cc i ca ilng o u vo.
- Lp li qu trnh o vi cc gi tr gim dn t gi tr cc i.Khi chun nhiu ln cho php xc nh ng cong chun theo c hai hng o
tng dn v o gim dn.
1.3. Cc c trng cbn
1.3.1. nhy ca cm bin
a) Khi nim
i vi cm bin tuyn tnh, gia bin thin u ra s v bin thin u vo m
c s lin h tuyn tnh:
m.Ss =
(1.2)
i lng S xc nh bi biu thcmsS
= c gi l nhy ca cm bin.
Trng hp tng qut, biu thc xc nh nhy S ca cm bin xung quanh gi tr mi
ca i lng o xc nh bi t s gia bin thin s ca i lng u ra v bin thin m
tng ng ca i lng o u vo quanh gi tr:
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
8/179
imm
m
sS
=
=
(1.3)
php o t chnh xc cao, khi thit k v s dng cm bin cn lm sao
cho nhy S ca n khng i, ngha l t ph thuc nht vo cc yu t sau:
- Gi tr ca i lng cn o m v tn s thay i ca n.- Thi gian s dng.- nh hng ca cc i lng vt l khc (khng phi l i lng o) ca mi
trng xung quanh.
Thng thng nh sn xut cung cp gi tr ca nhy S tng ng vi nhng iu
kin lm vic nht nh ca cm bin.
b) nhy trong ch tnh v t s chuyn i tnh
ng chun cm bin, xy dng trn cso cc gi tr siu ra tng ng vi ccgi tr khng i mi ca i lng o khi i lng ny t n ch lm vic danh nh
c gi l c trng tnh ca cm bin. Mt im Qi(mi,si) trn c trng tnh xc nh mt
im lm vic ca cm bin ch tnh.
Trong ch tnh, nhy S xc nh theo cng thc (1.3) chnh l c ca c
trng tnh im lm vic ang xt. Nh vy, nu c trng tnh khng phi l tuyn tnh th
nhy trong ch tnh ph thuc im lm vic.
i lng ri xc nh bi t s gia gi tr siu ra v gi tr miu vo c gi l
t s chuyn i tnh:
iQ
im
sr
=
(1.4)
T (1.4), ta nhn thy t s chuyn i tnh ri khng ph thuc vo im lm vic Qi v
ch bng S khi c trng tnh l ng thng i qua gc to.
c) nhy trong chng
nhy trong chng c xc nh khi i lng o bin thin tun hon theo
thi gian.
Gi s bin thin ca i lng o m theo thi gian c dng:
tcosmm)t(m 10 += (1.5)
Trong m0 l gi tr khng i, m1 l bin v tn s gc ca bin thin i lng
o.
u ra ca cm bin, hi p s c dng:
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
9/179
)tcos(ss)t(s 10 ++=
Trong :
- s0 l gi tr khng i tng ng vi m0 xc nh im lm vic Q0 trn ng congchun ch tnh.
- s1 l bin bin thin u ra do thnh phn bin thin ca i lng o gy nn.- l lch pha gia i lng u vo v i lng u ra.Trong chng, nhy S ca cm bin c xc nh bi t s gia bin ca
bin thin u ra s1 v bin ca bin thin u vo m1ng vi im lm vic c xt Q0,
theo cng thc:
0Q1
1
m
sS
=
nhy trong chng ph thuc vo tn si lng o, )f(SS = . S bin thin
ca nhy theo tn s c ngun gc l do qun tnh c, nhit hoc in ca u o, tc l
ca cm bin v cc thit b ph tr, chng khng th cung cp tc thi tn hiu in theo kp
bin thin ca i lng o. Bi vy khi xt s hi p c ph thuc vo tn s cn phi xem
xt s mch o ca cm bin mt cch tng th.
1.3.2. tuyn tnh
a) Khi nim
Mt cm bin c gi l tuyn tnh trong mt di o xc nh nu trong di ch
, nhy khng ph thuc vo i lng o.
Trong ch tnh, tuyn tnh chnh l s khng ph thuc ca nhy ca
cm bin vo gi tr ca i lng o, th hin bi cc on thng trn c trng tnh
ca cm bin v hot ng ca cm bin l tuyn tnh chng no i lng o cn nm
trong vng ny.
Trong chng, tuyn tnh bao gm s khng ph thuc ca nhy ch
tnh S(0) vo i lng o, ng thi cc thng s quyt nh s hi p (nh tn
s ring f0 ca dao ng khng tt, h s tt dn cng khng ph thuc vo i lng
o.
Nu cm bin khng tuyn tnh, ngi ta a vo mch o cc thit b hiu chnh
sao cho tn hiu in nhn c u ra t l vi s thay i ca i lng o u
vo. S hiu chnh c gi l s tuyn tnh ho.
b) ng thng tt nht
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
10/179
Khi chun cm bin, t kt qu thc nghim ta nhn c mt lot im tng
ng (si,mi) ca i lng u ra v i lng u vo. V mt l thuyt, i vi cc
cm bin tuyn tnh, ng cong chun l mt ng thng. Tuy nhin, do sai s khi
o, cc im chun (mi, si) nhn c bng thc nghim thng khng nm trn cng
mt ng thng.
ng thng c xy dng trn cscc s liu thc nghim sao cho sai s l
b nht, biu din s tuyn tnh ca cm bin c gi l ng thng tt nht.
Phng trnh biu din ng thng tt nht c lp bng phng php bnh phng
b nht. Gi s khi chun cm bin ta tin hnh vi N im o, phng trnh c dng:
bams +=
Trong :
( )2
i
2
i
iiii
mm.N
m.sm.s.N
a
=
( )
=
2
i2i
iii2ii
mm.N
m.s.mm.sb
c) lch tuyn tnh
i vi cc cm bin khng hon ton tuyn tnh, ngi ta a ra khi nim lch tuyn
tnh, xc nh bi lch cc i gia ng cong chun v ng thng tt nht, tnh bng
% trong di o.
1.3.3. Sai s v chnh xc
Cc b cm bin cng nh cc dng co lng khc, ngoi i lng cn o (cm
nhn) cn chu tc ng ca nhiu i lng vt l khc gy nn sai s gia gi tro c v
gi tr thc ca i lng cn o. Gi x l lch tuyt i gia gi tro v gi tr thc x
(sai s tuyt i), sai s tng i ca b cm bin c tnh bng:
100.x
x= [%]
Sai s ca b cm bin mang tnh cht c tnh bi v khng th bit chnh xc gi tr
thc ca i lng cn o. Khi nh gi sai s ca cm bin, ngi ta thng phn chng
thnh hai loi: sai s h thng v sai s ngu nhin.
- Sai s h thng: l sai s khng ph thuc vo s ln o, c gi tr khng i hocthay i chm theo thi gian o v thm vo mt lch khng i gia gi tr thc v gi tr
o c. Sai s h thng thng do s thiu hiu bit v ho, do iu kin s dng khng
tt gy ra. Cc nguyn nhn gy ra sai s h thng c th l:
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
11/179
Do nguyn l ca cm bin.
+ Do gi tr ca i lng chun khng ng.
+ Do c tnh ca b cm bin.
+ Do iu kin v ch s dng.
+Do x l kt quo.
- Sai s ngu nhin: l sai s xut hin c ln v chiu khng xc nh. Ta c th don c mt s nguyn nhn gy ra sai s ngu nhin nhng khng th don c
ln v du ca n. Nhng nguyn nhn gy ra sai s ngu nhin c th l:
+ Do s thay i c tnh ca thit b.
+ Do tn hiu nhiu ngu nhin.
+ Do cc i lng nh hng khng c tnh n khi chun cm bin.
Chng ta c th gim thiu sai s ngu nhin bng mt s bin php thc nghim thch
hp nh bo v cc mch o trnh nh hng ca nhiu, tng iu chnh in p ngun
nui, b cc nh hng nhit , tn s, vn hnh ng ch hoc thc hin php o lng
thng k.
1.3.4. nhanh v thi gian hi p
nhanh l c trng ca cm bin cho php nh gi kh nng theo kp v thi gian
ca i lng u ra khi i lng u vo bin thin. Thi gian hi p l i lng c s
dng xc nh gi tr s ca nhanh.
nhanh tr l khong thi gian t khi i lng o thay i t ngt n khi bin thin
ca i lng u ra ch cn khc gi tr cui cng mt lng gii hn tnh bng %. Thi
gian hi p tng ng vi % xc nh khong thi gian cn thit phi chi sau khi c s
bin thin ca i lng o ly gi tr ca u ra vi chnh xc nh trc. Thi gian hi
p c trng cho ch qu ca cm bin v l hm ca cc thng s thi gian xc nh
ch ny.
Trong trng hp s thay i ca i lng o c dng bc thang, cc thng s thi
gian gm thi gian tr khi tng (tdm) v thi gian tng (tm) ng vi s tng t ngt ca i
lng o hoc thi gian tr khi gim (tdc) v thi gian gim (tc) ng vi s gim t ngt ca
i lng o. Khong thi gian tr khi tng tdm l thi gian cn thit i lng u ra tngt gi tr ban u ca n n 10% ca bin thin tng cng ca i lng ny v khong thi
gian tng tm l thi gian cn thit i lng u ra tng t 10% n 90% bin thin bin
thin tng cng ca n. m
m0
t
0s
s
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
12/179
Tng t, khi i lng o gim, thi gian tr khi gim tdc l thi gian cn thit i
lng u ra gim t gi tr ban u ca n n 10% bin thin tng cng ca i lng
ny v khong thi gian gim tc l thi gian cn thit i lng u ra gim t 10% n
90% bin thin bin thin tng cng ca n.
Cc thng s v thi gian tr, tdm, tm, tdc, tc ca cm bin cho php ta nh gi v thi gian
hi p ca n.
1.3.5. Gii hn sdng ca cm bin
Trong qu trnh s dng, cc cm bin lun chu tc ng ca ng lc chc, tc ng
nhit... Khi cc tc ng ny vt qu ngng cho php, chng s lm thay i c trng lm
vic ca cm bin. Bi vy khi s dng cm bin, ngi s dng cn phi bit r cc gii hn
ny.
a) Vng lm vic danh nh
Vng lm vic danh nh tng ng vi nhng iu kin s dng bnh thng
ca cm bin. Gii hn ca vng l cc gi tr ngng m cc i lng o, cc i
lng vt l c lin quan n i lng o hoc cc i lng nh hng c th
thng xuyn t ti m khng lm thay i cc c trng lm vic danh nh ca cm
bin.
b) Vng khng gy nn hhng
Vng khng gy nn h hng l vng m khi m cc i lng o hoc cc i
lng vt l c lin quan v cc i lng nh hng vt qua ngng ca vng lm
vic danh nh nhng vn cn nm trong phm vi khng gy nn h hng, cc c
trng ca cm bin c th b thay i nhng nhng thay i ny mang tnh thun
nghch, tc l khi trv vng lm vic danh nh cc c trng ca cm bin ly li
gi tr ban u ca chng.
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
13/179
c) Vng khng ph hu
Vng khng ph hy l vng m khi m cc i lng o hoc cc i lng vt
l c lin quan v cc i lng nh hng vt qua ngng ca vng khng gy nn
h hng nhng vn cn nm trong phm vi khng b ph hy, cc c trng ca cm
bin b thay i v nhng thay i ny mang tnh khng thun nghch, tc l khi trv
vng lm vic danh nh cc c trng ca cm bin khng th ly li gi tr ban u
ca chng. Trong trng hp ny cm bin vn cn s dng c, nhng phi tin
hnh chun li cm bin.
1.4. Nguyn l chung ch to cm bin
Cc cm bin c ch to da trn c scc hin tng vt l v c phn
lm hai loi:
- Cm bin tch cc: l cc cm bin hot ng nh mt my pht, p ng (s)l in tch, in p hay dng.
- Cm bin thng: l cc cm bin hot ng nh mt trkhng trong p ng (s) l in tr, t cm hoc in dung.
1.4.1. Nguyn l ch to cc cm bin tch cc
Cc cm bin tch cc c ch to da trn csng dng cc hiu ng vt l
bin i mt dng nng lng no (nhit, choc bc x) thnh nng lng in.
Di y m t mt cch khi qut ng dng mt s hiu ng vt l khi ch to cm
bin.
a) Hiu ng nhit in
Hai dy dn (M1) v (M2) c bn cht ho hc khc nhau c hn li vi nhau
thnh mt mch in kn, nu nhit hai mi hn l T1 v T2 khc nhau, khi
trong mch xut hin mt sut in ng e(T1, T2) m ln ca n ph thuc chnh
lch nhit gia T1 v T2.
T1
T2
(M1)
(M2)
(M2)
e
Hnh 1.4. S hi u ng nhi t i n.
T1
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
14/179
Hiu ng nhit in c ng dng o nhit T1 khi bit trc nhit T2,
thng chn T2 = 0oC.
b) Hiu ng hoin
Mt s tinh th gi l tinh th hoin (v d tinh th sulfate triglycine) c tnh
phn cc in t pht vi phn cc ph thuc vo nhit , lm xut hin trn cc
mt i din ca chng nhng in tch tri du. ln ca in p gia hai mt ph
thuc vo phn cc ca tinh th hoin.
Hiu ng hoin c ng dng o thng lng ca bc x nh sng. Khi ta
chiu mt chm nh sng vo tinh th hoin, tinh th hp th nh sng v nhit
ca n tng ln, lm thay i s phn cc in ca tinh th. o in p V ta c th
xc nh c thng lng nh sng .
c) Hiu ng p inMt s vt liu gi chung l vt liu p in (nh thch anh chng hn) khi b bin dng
dc tc ng ca lc chc, trn cc mt i din ca tm vt liu xut
hin nhng lng in tch bng nhau nhng tri du, c gi l hiu ng p in. o V ta
c th xc nh c cng ca lc tc dng F.
d) Hiu ng cm ng in t
v
Hnh 1.5 ng d ng hi u ng ho i n
V F
Hnh 1.6 ng d ng hi u ng p i n
F
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
15/179
Khi mt dy dn chuyn ng trong t trng khng i, trong dy dn xut hin
mt sut in ng t l vi t thng ct ngang dy trong mt n v thi gian, ngha
l t l vi tc dch chuyn ca dy. Tng t nh vy, trong mt khung dy t
trong t trng c t thng bin thin cng xut hin mt sut in ng t l vi tc
bin thin ca t thng qua khung dy.
Hiu ng cm ng in tc ng dng xc nh tc dch chuyn ca vt
thng qua vic o sut in ng cm ng.
e) Hiu ng quang in
- Hiu ng quang dn: (hay cn gi l hiu ng quang in ni) l hin tng
gii phng ra cc ht dn t do trong vt liu (thng l bn dn) khi chiu vo chng
mt bc x nh sng (hoc bc xin t ni chung) c bc sng nh hn mt
ngng nht nh.
- Hiu ng quang pht xin t: (hay cn gi l hiu ng quang in ngoi)
l hin tng cc in tc gii phng v thot khi b mt vt liu to thnh dng
c th thu li nhtc dng ca in trng.
g) Hiu ng quang - in - t
Khi tc dng mt t trng B vung gc vi bc x nh sng, trong vt liu bn
dn c chiu sng s xut hin mt hiu in th theo hng vung gc vi t
trng B v hng bc x nh sng.
h) Hiu ng Hall
e
Hnh 1.7 ng d ng hi u ng c m ng i n t
B
B
V
Hnh 1.8 ng d ng hi u ng quang - i n - t
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
16/179
Khi t mt tm mng vt liu mng (thng l bn dn), trong c dng in chy
qua, vo trong mt t trng B c phng to vi dng in I trong tm mt gc , s xut
hin mt hiu in th VH theo hng vung gc vi B v I. Biu thc hiu in th c
dng:
= sin.B.I.KV HH
Trong KH l h s ph thuc vo vt liu v kch thc hnh hc ca tm vt liu.
Hiu ng Hall c ng dng xc nh v tr ca mt vt chuyn ng. Vt cn xc
nh v tr lin kt chc vi thanh nam chm, mi thi im, v tr thanh nam chm xc
nh gi tr ca t trng B v gc tng ng vi tm bn dn mng lm vt trung gian. V
vy, hiu in th VHo c gia hai cnh tm bn dn l hm ph thuc vo v tr ca vt
trong khng gian.
1.4.2. Nguyn ch to cm bin thngCm bin thng thng c ch to t mt trkhng c cc thng s ch yu nhy
vi i lng cn o. Gi tr ca trkhng ph thuc kch thc hnh hc, tnh cht in ca
vt liu ch to (nhin trsut , t thm , hng sin mi ). V vy tc ng ca
i lng o c thnh hng ring bit n kch thc hnh hc, tnh cht in hoc ng
thi c hai.
S thay i thng s hnh hc ca trkhng gy ra do chuyn ng ca phn t chuyn
ng hoc phn t bin dng ca cm bin. Trong cc cm bin c phn t chuyn ng, mi
v tr ca phn tng sng vi mt gi tr xc nh ca trkhng, cho nn o trkhng c
th xc nh c v tr ca i tng. Trong cm bin c phn t bin dng, s bin dng ca
phn t bin dng di tc ng ca i lng o (lc hoc cc i lng gy ra lc) gy ra
s thay i ca trkhng ca cm bin. S thay i trkhng do bin dng lin quan n lc
tc ng, do lin quan n i lng cn o. Xc nh trkhng ta c th xc nh c
i lng cn o.
B
SN
v
X
X
Hnh 1.9 ng d ng hi u ng Hall
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
17/179
S thay i tnh cht in ca cm bin ph thuc vo bn cht vt liu ch to tr
khng v yu t tc ng (nhit , chiu sng, p sut, m ...). ch to cm bin,
ngi ta chn sao cho tnh cht in ca n ch nhy vi mt trong cc i lng vt l trn,
nh hng ca cc i lng khc l khng ng k. Khi c th thit lp c s ph
thuc n tr gia gi tri lng cn o v gi tr trkhng ca cm bin.
Trn bng 1.1 gii thiu cc i lng cn o c kh nng lm thay i tnh cht
in ca vt liu s dng ch to cm bin.
Bng 1.1
i lng cn o c trng nhy cm Loi vt liu s dng
Nhit Kim loi (Pt, Ni, Cu)
Bn dn
Bc x nh sng Bn dn
Bin dng T thm ()Hp kim Ni, Si pha tpHp kim st t
V tr (nam chm) Vt liu tin tr:Bi, InSb
1.5. Mch o
1.5.1. S mch o
Mch o bao gm ton b thit bo (trong c cm bin) cho php xc nh chnh
xc gi tr ca i lng cn o trong nhng iu kin tt nht c th.
u vo ca mch, cm bin chu tc ng ca i lng cn o gy nn tn hiu inmang theo thng tin vi cn o.
u ra ca mch, tn hiu in qua x l c chuyn i sang dng c thc
c trc tip gi tr cn tm ca i lng o. Vic chun ho m bo cho mi gi tr ca
ch thu ra tng ng vi mt gi tr ca i lng o tc ng u vo ca mch.
Dng n gin ca mch o gm mt cm bin, b phn bin i tn hiu v thit b ch
th, v d mch o nhit gm mt cp nhit ghp ni trc tip vi mt milivn k.
V
Hnh 1.10 S m ch o nhi t b ng c p nhi t
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
18/179
Trn thc t, do cc yu cu khc nhau khi o, mch o thng gm nhiu thnh
phn trong c cc khi ti u ho vic thu thp v x l d liu, chng hn
mch tuyn tnh ho tn hiu nhn t cm bin, mch khin dung k sinh, cc b
chuyn i nhiu knh, b khuch i, b so pha lc nhiu, b chuyn i tng t -
s, b vi x l, cc thit b h tr... Trn hnh 1.11 biu din s khi mt mch in
o in th trn b mt mng nhy quang c lp rp t nhiu phn t
1.5.2. Mt s phn tcbn ca mch o
a) B khuch i thut ton (KTT)
B khuch i thut ton mch tch hp l b khuch i dng mt chiu c hai u vo
v mt u ra chung, thng gm hng trm tranzito v cc in tr, tin ghp ni vi
nhau. S b khuch i thut ton biu din trn hnh 1.12.
Cc c tnh cbn ca b khuch i thut ton:- B khuch i c hai u vo: mt u o (-), mt u khng o (+).- in trvo rt ln, chng trm Mn G.- in trra rt nh, cphn chc .- in p lch u vo rt nh, cvi nV.- H s khuch i hmch rt ln, c100.000.- Di tn lm vic rng.
FC(1)
D(2)
PA(3)
PC(4)
(5) ADC(6)
My in
CPU(7)
Mnhnh
Hnh 1.11 M ch o i n th b m t1) My pht ch c n ng 2) C m bi n i n tch 3) Ti n khu ch i
4) So pha l c nhi u 5) Khu ch i 6) Chuy n i t ng t s 7) My tnh
+
Hnh 1.12 S b khu ch i thu t ton
K
Ura = K.Uvo
Ura
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
19/179
- H s suy gim theo cch ni chung CMRR l t s h s khuch i ca b khuchi thut ton i vi cc tn hiu sai lch v h s khuch i theo cch ni chung ca cng
b khuch i thut ton. Thng thng CMRR vo khong 90 dB.
- Tc tng hn ch s bin thin cc i ca in p tnh bng V/s.b) B khuch i o lng IA
B khuch i o lng IA c hai u vo v mt u ra. Tn hiu u ra t l vi hiu
ca hai in p u vo:
UA)UU(AU ra == +
u vo vi sai ng vai tr rt quan trng trong vic kh nhiu ch chung v tng
in trvo ca KTT. in p trn Raphi bng in p vi sai u vo U v to nn dng
inaR
U
i
= . Cc in p ra t KTT U1 v U2 phi bng nhau v bin nhng ngc
pha. in p U3 ca tng th hai bin i u ra vi sai thnh u ra n cc. H s khuch i
tng ca IA bng:
1
3
a R
R
R
R21A
+=
c) Khin p lch
i vi mt b khuch KTT l tng khi hmch phi c in p ra bng
khng khi hai u vo ni mt. Thc t v cc in p bn trong nn to ra mt in pnh (in p phn cc) u vo KTT cvi mV, nhng khi s dng mch kn in
p ny c khuch i v to nn in p kh ln u ra. khin p lch c
th s dng s hnh 1.14, bng cch iu chnh bin trR3.
Hnh 1.13 S b khu ch i o l ng g m ba K TT ghp n i i n tr
+
+
+
R10k
R10k
Ra1k
R2 10k R3 10k
R2 10k
R3190k
U1
U2
U3
u ra
+
+ 9V
R310k
R2100k
- 9V
u ra
+
1
2
3
4 5
6714
7
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
20/179
d) Mch lp li in p
lp li in p chnh xc, ngi ta s dng b KTT lm vic ch khng
o vi h s khuch i bng 1 s nh hnh 1.15.
Trong b lp in p, cc dng ca KTT c ni trc tip vi tn hiu vo,
cn cc m c ni trc tip vi u ra, to nn in p phn hi 100% do h s
khuch i bng 1. Mch lp in p c chc nng tng in tr u vo, do vy
thng dng ni gia hai khu trong mch o.
e) Mch cu
Cu Wheatstone thng c s dng trong cc mch o nhit , lc, p sut,
t trng... Cu gm bn in trR1, R2, R3 cnh v R4 thay i (mc nh hnh
1.16) hot ng nh cu khng cn bng da trn vic pht hin in p qua ngcho ca cu.
Hnh 1.15 S m ch l p i n p
+ 9V
- 9V
u ra
+
2
3
4
6714
u vo
7
Hnh 1.15 S m ch c u
+
R1 R3
R2R4 = R(1+)
U Vra
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
21/179
Trong mch cu, in p ra l hm phi tuyn nhng i vi bin i nh
(> R2 hoc R2 >> R1 in p ra ca cu gim. t K = R1/R2 nhy
ca cu l:
( )2k1
K
R
U
+= .
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
22/179
Chng II
Cm bin quang
2.1.Tnh cht v n vo nh sng
2.1.1. Tnh cht ca nh sng
Nh chng ta bit, nh sng va c tnh cht sng va c tnh cht ht.
nh sng l mt dng ca sng in t, vng nh sng nhn thy c bc sng t 0,4 -
0,75 m. Trn hnh 2.1 biu din ph nh sng v s phn chia thnh cc di mu ca ph.
Vn tc truyn nh sng trong chn khng c = 299.792 km/s, trong mi trng vt cht
vn tc truyn sng gim, c xc nh theo cng thc:
ncv =
n - chit sut ca mi trng.
Mi quan h gia tn s v bc sng ca nh sng xc nh bi biu thc:
- Khi mi trng l chn khng :
=c
- Khi mi trng l vt cht :
=v
.
Trong l tn s nh sng.Tnh cht ht ca nh sng th hin qua s tng tc ca nh sng vi vt cht.
nh sng gm cc ht nh gi l photon, mi ht mang mt nng lng nht nh,
nng lng ny ch ph thuc tn s ca nh sng:
= hW
(2.1)
0,3
95
0,4
55
0,4
90
0,5
75
0,5
90
0,6
50
0,7
50
c c tm tm lam l cvng
da cam h ng ngo i
0,01 0,1 0,4 0,75 1,2 10 30 100
c c tm h ng ngo i h. ngo i xa
trngth
y
h.n.ng
n
( m)
Hnh 2.1 Ph nh sng
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
23/179
Trong h l hng s Planck (h = 6,6256.10-34J.s).
Bc sng ca bc x nh sng cng di th tnh cht sng th hin cng r,
ngc li khi bc sng cng ngn th tnh cht ht th hin cng r.
2.1.2. Cc n vo quang
a) n vo nng lng
- Nng lng bc x (Q): l nng lng lan truyn hoc hp th di dng bc xo
bng Jun (J).
- Thng lng nh sng (): l cng sut pht x, lan truyn hoc hp tho bng oat
(W):
dt
dQ=
(2.2)
- Cng nh sng (I): l lung nng lng pht ra theo mt hng cho trc ng
vi mt n v gc khi, tnh bng oat/steriadian.
=d
dI
(2.3)
- chi nng lng (L): l t s gia cng nh sng pht ra bi mt phn t b
mt c din tch dA theo mt hng xc nh v din tch hnh chiu dAn ca phn t
ny trn mt phng P vung gc vi hng .
ndA
dIL =
(2.4)
Trong dAn = dA.cos, vi l gc gia P v mt phng cha dA.
chi nng lng o bng oat/Steriadian.m2.
- ri nng lng (E): l t s gia lung nng lng thu c bi mt phn t bmt v din tch ca phn t.
dA
dE
=
(2.5)
ri nng lng o bng oat/m2.
b) n vo th gic
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
24/179
nhy ca mt ngi i vi nh sng c bc sng khc nhau l khc nhau.
Hnh 2.2 biu din nhy tng i ca mt V() vo bc sng. Cc i lng th
gic nhn c ti lng nng lng tng ng thng qua h s t l K.V().
Theo quy c, mt lung nh snh c nng lng 1W ng vi bc sng max
tng ng vi lung nh sng bng 680 lumen, do K=680.
Do vy lung nh sng n sc tnh theo n vo th gic:
( ) ( ) ( )= V680V lumen
i vi nh sng ph lin tc:
=
dd
)(d)(V680
2
1
V lumen
Tng t nh vy ta c th chuyn i tng ng cc n vo nng lng v
n vo th gic.
Bng 2.1 lit k cc n vo quang cbn.
Bng 2.1
i lng o n v th gic n v nng lng
Lung (thng lng) lumen(lm) oat(W)
Cng cadela(cd) oat/sr(W/sr)
chi cadela/m2 (cd/m2) oat/sr.m2 (W/sr.m2)
ri lumen/m2 hay lux (lx) oat/m2 (W/m2)
Nng lng lumen.s (lm.s) jun (j)
2.2.Cm bin quang dn
2.2.1. Hiu ng quang dn
Hnh 2.2 ng cong nh y t ng i c a m t
(m)
V()
0,3 0,4 0,5 0,6 0,7 0,8
0
0,5
1
max
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
25/179
Hiu ng quang dn (hay cn gi l hiu ng quang in ni) l hin tng gii
phng nhng ht ti in (ht dn) trong vt liu di tc dng ca nh sng lm tng
dn in ca vt liu.
Trong cht bn dn, cc in t lin kt vi ht nhn, gii phng in t khi
nguyn t cn cung cp cho n mt nng lng ti thiu bng nng lng lin kt Wlk.
Khi in tc gii phng khi nguyn t, s to thnh ht dn mi trong vt liu.
Ht dn c gii phng do chiu sng ph thuc vo bn cht ca vt liu b
chiu sng. i vi cc cht bn dn tinh khit cc ht dn l cp in t - l trng.
i vi trng hp bn dn pha tp, ht dn c gii phng l in t nu l pha tp
dono hoc l l trng nu l pha tp acxepto.
Gi s c mt tm bn dn phng th tch V pha tp loi N c nng cc donor
Nd, c mc nng lng nm di vng dn mt khong bng Wd ln nhit
phng v khi trong ti nng n0 ca cc donor b ion ho do nhit l nh.
+ l tr ng
- i n t
h
+ l tr ng
h-
- i n t
h+
Hnh 2.3. nh h ng c a b n ch t v t li u n h t d n c gi i phng
+ ++Wd
+ +++
h hVng d n
Vng ho
Hnh 2.4. T bo quang d n v s chuy n m c n ng l ng c a i n t
L
V
chi u sng
A
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
26/179
Khi trong ti, nng in t c gii phng trong mt n v thi gian t l
vi nng cc tp cht cha b ion ho v bng a(Nd -no), vi h s a xc nh theo
cng thc:
=kT
qWexpa d
(2.6)
Trong q l tr tuyt i ca in tch in t, T l nhit tuyt i ca khi
vt liu, k l hng s.
Sin t ti hp vi cc nguyn t b ion ho trong mt n v thi gian t l
vi cc nguyn t b ion ho n0 v nng in t cng chnh bng n0 v bng
r. 20n , trong r l h s ti hp.
Phng trnh ng hc biu din s thay i nng in t t do trong khi
vt liu c dng:
( ) 200d0 n.rnNa
dt
dn=
trng thi cn bng ta c : 0dt
dn0 =
Suy ra:
2/1
d
2
2
0r
N.a
r4
a
r.2
an
++=
(2.7)
dn trong ti c biu din bi h thc:
00 nq= (2.8)
Trong l linh ng ca in t.
Khi nhit tng, linh ng ca in t gim, nhng s tng mt in t
t do do s kch thch nhit ln hn nhiu nn nh hng ca n l nhn t quyt nh
i vi dn.
Khi chiu sng, cc photon s ion ho cc nguyn t donor, gii phng ra cc
in t. Tuy nhin khng phi tt c cc photon p ti b mt vt liu u gii phng
in t, mt s b phn x ngay b mt, mt s b hp th v chuyn nng lng cho
in t di dng nhit nng, ch phn cn li mi tham gia vo gii phng in t. Do
vy, sin t (g) c gii phng do b chiu sng trong mt giy ng vi mt n
v th tch vt liu, xc nh bi cng thc:
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
27/179
( )
==h
R1.
L.A
1
V
Gg
(2.9)
Trong :
G - sin tc gii phng trong th tch V trong thi gian mt giy.
V=A.L, vi A, L l din tch mt cnh v chiu rng tm bn dn (hnh 2.4).
- hiu sut lng t (sin t hoc l trng trung bnh c gii phng khi
mt photon b hp th).
R - l h s phn x ca b mt vt liu.
- bc sng nh sng.
- thng lng nh sng.
h - hng s Planck.
Phng trnh ng hc ca ti hp trong trng hp ny c dng:
( ) 2d n.rgnNadt
dn+=
Thng thng bc x chiu ti ln sin tc gii phng ln hn
rt nhiu so vi in tc gii phng do nhit:
( )nNag d >> v n>>n0
Trong iu kin trn, rt ra phng trnh ng hc cho mt in tiu kin cn
bng di tc dng chiu sng:2/1
r
gn
=
(2.10)
dn tng ng vi nng in tiu kin cn bng:
nq= .
(2.11)
T cng thc (2.9), (2.10) v (2.11) ta nhn thy dn l hm khng tuyn tnh
ca thng lng nh sng, n t l vi 1/2. Thc nghim cho thy s m ca hm
nm trong khong 0,5 - 1.
2.2.2. T bo quang dn
a) Vt liu ch to
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
28/179
T bo quang dn c ch to cc bn dn a tinh thng nht hoc n tinh
th, bn dn ring hoc bn dn pha tp.
- a tinh th: CdS, CdSe, CdTe.
PbS, PbSe, PbTe.
- n tinh th: Ge, Si tinh khit hoc pha tp Au, Cu, Sb, In.
SbIn, AsIn, PIn, cdHgTe.
Vng ph lm vic ca cc vt liu ny biu din trn hnh 2.5
b) Cc c trng
- in tr: Gi trin trti RC0 ca cc quang in trph thuc rt ln vo hnh
dng hnh hc, kch thc, nhit v bn cht ho l ca vt liu ch to. Cc cht
PbS, CdS, CdSe c in trti rt ln ( t 104 - 10925oC), trong khi SbIn,
SbAs, CdHgTe c in trti tng i nh ( t 10 - 10325oC). in tr Rc
ca cm bin gim rt nhanh khi ri tng ln. Trn hnh 2.6 l mt v d v s thayi ca in trcm bin theo ri sng.
Hnh 2.5. Vng ph lm vi c c a m t s v t li u quang d n
0,2 0,6 1 2 3 4 5 10 20 30
CdS
CdSeCdTe
PbSPbSe
PbTeGe
Si
GeCuSnIn
AsInCdHg
, m
i n tr ()
102
104
106
106
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
29/179
T bo quang dn c th coi nh mt mch tng ng gm hai in trRc0 v
Rcp mc song song:
cpco
cpco
cRR
RRR
+=
(2.12)
Trong :
Rco - in trtrong ti.
Rcp - in trkhi chiu sng:= aRcp .
a - h s ph thuc vo bn cht vt liu, nhit , ph bc x.
- h s c gi tr t 0,5 - 1.
Thng thng Rcp
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
30/179
Trong iu kin s dng thng thng I0
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
31/179
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
32/179
- Thu tn hiu quang: dng t bo quang dn thu v bin tn hiu quang thnhxung in. Cc xung nh sng ngt qung c th hin qua xung in, trn cs
c th lp cc mch m vt hoc o tc quay ca a.
2.2.3. Photoiot
a) Cu to v nguyn l hot ng
Xt hai tm bn dn, mt thuc loi N v mt thuc loi P, ghp tip xc nhau. Ti
mt tip xc hnh thnh mt vng ngho ht dn v ti vng ny tn ti mt in
trng v hnh thnh hng ro th Vb.
Khi khng c in th ngoi t ln chuyn tip (V=0), dmg in chy qua
chuyn tip i = 0, thc t dng I chnh l dng tng cng ca hai dng in bng nhau
v ngc chiu:
- Dng khuch tn cc ht cbn sinh ra khi ion ho cc tp cht (l trong trongbn dn loi P, in t trong bn dn loi N) do nng lng nhit ca cc ht dn c
bn ln vt qua hng ro th.
- Dng ht dn khng cbn sinh ra do kch thch nhit (in t trong bn dn P,l trng trong bn dn N) chuyn ng di tc dng ca in trng E trong vng
ngho.
Hnh 2.9 Dng t bo quang d n i u khi n r lea) i u khi n tr c ti p b) i u khi n thng qua tranzito khu ch i
+ +
Vng chuy n ti p
E
P N
Vng ngho
Vb
Hnh 2.10 S chuy n ti p P - N v hi u ng quang i n trong vng ngho
+
N
P
h
+
Ir
Vng ngho
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
33/179
Khi c in p t ln it, hng ro th thay i ko theo s thay i dng ht c
bn v b rng vng ngho. Dng in qua chuyn tip:
0d
0 IkT
qVexpII
=
Khi in p ngc ln (Vd
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
34/179
b) Ch hot ng
- Ch quang dn:
S nguyn l (hnh 2.12a) gm mt ngun Es phn cc ngc it v mt in
trRm o tn hiu.
Dng ngc qua it:
p0d
0r IIkT
qVexpII ++
=
(2.40)
Trong Ip l dng quang in:
( )( )Xexp
hc
R1qI 0p
=
(2.41)
Khi in p ngc Vd ln, thnh phn
kT
qVexp d 0, ta c:
P0R III +=
Thng thng I0
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
35/179
im lm vic ca it l im giao nhau gia ng thng ti v ng c tuyn
i-V vi thng lng tng ng. Ch lm vic ny l tuyn tnh, VR t l vi thng
lng.
- Ch quang th:
Trong ch ny khng c in p ngoi t vo it. it lm vic nh mt bchuyn i nng lng tng ng vi mt my pht v ngi ta o th hmch V0C
hoc o dng ngn mch ISC.
o th hmch: Khi chiu sng, dng IP tng lm cho hng ro th gim mt
lng Vb. S gim chiu cao hng ro th lm cho dng ht dn cbn tng ln, khi
t cn bng Ir= 0.
Ta c: 0IIkT
qVexpI p0
d0 =++
Rt ra:
+=
0
Pb
I
I1log
q
kTV
gim chiu cao Vb ca hng ro th c th xc nh c thng qua o in
p gia hai u it khi hmch.
+=
0
POC
I
I1log
q
kTV
Khi chiu sng yu IP I0 v ta c:
0
POC
I
Ilog
q
kTV =
Trong trng hp ny VOC c gi tr tng i ln (c0,1 - 0,6 V) nhng ph thuc
vo thng lng theo hm logarit.
0,2
0,4
VOC, V
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
36/179
o dng ngn mch:Khi ni ngn mch hai u it bng mt in trnh hn rd
no , dng on mch ISC chnh bng IP v t l vi thng lng (hnh 2.14):
PSC II =
c im quan trng ca ch ny l khng c dng ti, nhvy c th gimnhiu v cho php o c thng lng nh.
c) nhy
i vi bc x c ph xc nh, dng quang in IP t l tuyn tnh vi thng
lng trong mt khong tng i rng, c5 - 6 decad. nhy ph xc nh theo
cng thc:
( ) ( )
=
=hc
XexpR1qI)(S P
Vi s.
nhy ph ph thuc vo , hiu sut lng t, h s phn x R v h s
hp th.
Hnh 2.14 S ph thu c c a dng ng nm ch vo thng l ng nh sng
ISC,V
Thng l ng, mW
0
10
20
0,1 0,2
1,0
0,6
0,4
0,2
0,1
0,04
S()S(P)
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
37/179
Ngi s dng cn phi bit nhy ph da trn ng cong ph hi p
S()/S(P) v gi tr ca bc sng P ng vi nhy cc i. Thng thng S(P)
nm trong khong 0,1 - 1,0 A/W.
Khi nhit tng, cc i P ca ng cong ph dch chuyn v pha bc
sng di. H s nhit ca dng quang dndT
dI.
I
1 P
P
c gi tr khong0,1%/oC.
d) Sng dng photodiot
- S lm vic ch quang dn:
c trng ca ch quang dn:
+ tuyn tnh cao.
+ Thi gian hi p ngn.+ Di thng ln.
Hnh 2.16 trnh by so dng ngc trong ch quang dn.
S cs(hnh 2.17a):
r1
2m0 I
R
R1RV
+=
0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 (m)
0
0,1
0,2
0,3
0,4
S (A/W)
Hnh 2.16 S ph thu c c a nh y vo nhi t
T1
T2>T1
T2
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
38/179
Khi tng in trRm s lm gim nhiu. Tng trvo ca mch khuch i phi
ln trnh lm gim in trti hiu dng ca it.
S tc ng nhanh (hnh 2.17b):
( ) r210 IRRV +=
in trca iot nh v bngK
RR 21 + trong K l h s khuch i tn s lm vic.
T C2 c tc dng b trnh hng ca t k sinh Cpl vi iu kin 22pl1 CRCR = . B
khuch i y phi c dng vo rt nh v s suy gim do nhit cng phi khng
ng k.
- S lm vic ch quang th:
c trng ca ch quang th:
+ C th lm vic ch tuyn tnh hoc logarit tu thuc vo ti.+ t nhiu.
+ Thi gian hi p ln.
+ Di thng nh.
+ Nhy cm vi nhit ch logarit.
S tuyn tnh (hnh 2.18a): o dng ngn mch Isc.
Trong ch ny:
scm0 I.RV =
S logarit(hnh 2.18b): o in p hmch Voc.
oc1
20 V
R
R1V
+=
ES
Rm
Ir
R1
R2
V0
CP1
Rm
ESR1+R2
R1
V0
R2
Hnh 2.17 S m ch o dng ng c trong ch quang d n
a) b)
++
C2+
VcoR1
R2
V0
+_IOC
R1=Rm
Rm
V0
_
+
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
39/179
2.2.4. Phototranzito
a) Cu to v nguyn l hot ng
Phototranzito l cc tranzito m vng baz c th c chiu sng, khng c
in p t ln baz, ch c in p trn C, ng thi chuyn tip B-C phn cc ngc.
in p t vo tp trung hu nh ton b trn chuyn tip B-C (phn cc
ngc) trong khi chnh lch in p gia E v B thay i khng ng k (VBE
0,6-0,7 V). Khi chuyn tip B-C c chiu sng, n hot ng ging nh photoiot
ch quang th vi dng ngc:
P0r III +=
Trong I0 l dng ngc trong ti, IP l dng quang in di tc dng ca thng
lng 0 chiu qua b dy X ca baz(bc sng < S):
( )0P hc
)Xexp(R1qI
=
Dng Irng vai tr dng baz, n gy nn dng colectIc:
( ) ( ) ( ) p0rc I1I1I1I +++=+=
- h s khuch i dng ca tranzito khi u chung emit.
C th coi phototranzito nh t hp ca mt photodiot v mt tranzito (hnh 2.19b).
Phodiot cung cp dng quang in ti baz, cn tranzito cho hiu ng khch i .
Hnh 2.19 Phototranzitoa) S m ch i n b) S t ng ng
c) Tch c p i n t l tr ng khi chi u sng baz
a) b) c)
|+
i n th
CBE
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
40/179
Cc in t v l trng pht sinh trong vng baz(di tc dng ca nh sng) s b
phn chia di tc dng ca in trng trn chuyn tip B - C.
Trong trng hp tranzito NPN, cc in t b ko v pha colecttrong khi l
trng b gi li trong vng baz(hnh 2.19c) to thnh dng in t t E qua B n C.
Hin tng xy ra tng t nh vy nu nh l trng phun vo bazt mt ngun bn
ngoi: in th baz tng ln lm gim hng ro th gia E v B, iu ny gy nn
dng in t IE chy t E n B v khuch tn tip t B v pha C.
b) nhy
Khi nhn c thng lng 0, iot baz-colectsinh ra dng quang in Ip,
dng ny gy nn trong phototranzito mt dng ( ) pcp I1I += , trong gi tr ca Icp
c rt ra t cng thc ca Ip:
( ) ( ) ( ) 0cp hc XexpR1q1I +=
i vi mt thng lng 0 cho trc, ng cong ph hi p xc nh bi
bn cht ca iot B-C: vt liu ch to (thng l Si) v loi pha tp (hnh 2.20). i
vi mt bc sng cho trc, dng colectIc khng phi l hm tuyn tnh ca thng
lng hoc chiu sng bi v h s khuch i ph thuc vo dng Ic (tc l cng
ph thuc thng lng), ngha l0
cI
ph thuc vo 0.
nhy ph S(p) bc sng tng ng vi im cc i c gi tr nm trong
khong 1 - 100A/W.
c) S dng phototranzito
Phototranzito c th dng lm b chuyn mch, hoc lm phn t tuyn tnh.
ch chuyn mch n c u im so vi photodiot l cho php s dng mt cch
S()S(p)(%)
100
80
60
40
20
0,4 0,6 0,8 1,0
(m)
Hnh 2.20 ng cong ph h i p c a photodiot
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
41/179
trc tip dng chy qua tng i ln. Ngc li, ch tuyn tnh, mc d cho
khuch i nhng ngi ta thch dng photoiot v n c tuyn tnh tt hn.
- Phototranzito chuyn mch:
Trong trng hp ny s dng thng tin dng nh phn: c hay khng c bc
x, hoc nh sng nh hn hay ln hn ngng. Tranzito chn hoc bo ho cho php
iu khin trc tip (hoc sau khi khuch i) nh mt rle, iu khin mt cng logic
hoc mt thyristo (hnh 2.21).
- Phototranzito trong ch tuyn tnh:
C hai cch s dng trong ch tuyn tnh.
- Trng hp th nht: o nh sng khng i (ging nh mt luxmet).
- Trng hp th hai: thu nhn tn hiu thay i dng:
( ) ( )tt 10 +=
( ) ( )t.SItI 10cc +=
2.2.5. Phototranzito hiu ng trng
Phototranzito hiu ng trng (photoFET) c s tng ng nh hnh
2.23.
++
++ +
Hnh 2.21 Photodiotzito trong ch chuy n m cha) R le b) R le sau kh ch i c) C ng logic d) Thyristo
+
Hnh 2.22 S nguyn l luxmet
Trong 1(t) l thnh ph n
thay i v i bin nh sao cho
khng d n t i phototranzito b ch n
ho c b o ho v c th coi hh y
khng i. Trong i u ki n , dng
colect c d ng:
G
D
SS
G
D
+
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
42/179
Trong phototranzito hiu ng trng, nh sng c s dng lm thay i in tr
knh. Vic iu khin dng mng IDc thc hin thng qua s thay i in p VGS gia
cng v ngun. Trong ch phn cc ngc chuyn tip P-N gia cng v knh, in p
ny s xc nh rng ca knh v do dng mng c dng:
2
P
GSDSSD
V
V1II
+=
Vi IDS - dng mng khi VGS = 0.
VP - in p tht knh.
Khi b chiu sng, chuyn tip P-N hot ng nh mt photodiot cho dng ngc:
P0r III +=
IP = Sg - dng quang in.
I0 - dng in trong ti.
Sg - nhy ca iot cng - knh.
- thng lng nh sng.
Dng Irchy qua in trRg ca mch cng xc nh in th VGS v v dng mng:
( ) gP0gGS EIIRV +=
Eg - th phn cc ca cng.
Phototranzito hiu ng trng c ng dng nhiu trong vic iu khin in
p bng nh sng.
2.3.Cm bin quang in pht x
2.3.1. Hiu ng quang in pht x
Hiu ng quang in pht x hay cn c gi l hiu ng quang in ngoi l
hin tng cc in tc gii phng khi b mt vt liu to thnh dng khi chiu
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
43/179
vo chng mt bc x nh sng c bc sng nh hn mt ngng nht nh v c th
thu li nhtc dng ca in trng.
Cch pht xin t khi chiu sng vt liu xy ra theo ba giai on:
- Hp th photon v gii phng in t bn trong vt liu.- in t va c gii phng di chuyn n b mt.- in t thot khi b mt vt liu.
Khi mt in t hp th photon v c gii phng, di chuyn ca n trong khi
vt liu mang tnh ngu nhin theo mi hng, do ch mt lng rt nh hng ti
b mt. Mt khc, trong qu trnh di chuyn, cc in t ny c th va chm vi cc
in t khc v mt i mt phn nng lng do ch mt lng nhin tc gii
phng ti c b mt. Mt khc, s pht x ca cc in t sau khi n c b
mt ch c th xy ra khi ng nng ca n thng c hng ro th phn cch vt
liu vi mi trng.
Vi tt c nhng iu kin trn, sin t pht x trung bnh khi mt photon b
hp th (hiu sut lng t ) thng nh hn 10% v t khi vt qu 30%.
Vt liu ch to: Ph thuc vo bc sng nh sng, vt liu ch to photocatot
c th chn trong cc loi sau:
- AgOCs nhy vng hng ngoi.
- Cs3Sb, (Cs)Na2KSb v K2CsSb: nhy vi nh sng nhn thy v vng t ngoi.
- Cs2Te, Rb2Te v CsTe ch nhy trong vng t ngoi.
Hiu sut lng t ca cc vt liu trn ~ 1 - 30%.
Ngoi ra cn dng cc hp cht ca cc cht thuc nhm III - V, l cc hp cht
GaAsxSb1-x , Ga1-xInxAs, InAsxP1-x, ngng nhy sng ca chng nm vng hng
ngoi ( ~1m), hiu sut lng tt ti 30%.
2.3.2. T bo quang in chn khng
T bo quang in chn khng gm mt ng hnh tr c mt ca s trong sut,
c ht chn khng (p sut ~ 10-6
- 10-8
mmHg). Trong ng t mt catot c khnng pht x khi c chiu sng v mt anot.
A
K
A
K
AK
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
44/179
S tng ng v s thay i ca dng anot Ia ph thuc vo in th anot - catot
Vakbiu din trn hnh 2.25.
c trng I - V c hai vng r rt:
+ Vng in tch khng gian c trng bi s tng mnh ca dng khi in p
tng.
+ Vng bo ho c trng bi s ph thuc khng ng k ca dng vo in
p.T bo quang in c s dng ch yu trong vng bo ho, khi n ging
nh mt ngun dng, gi tr ca dng ch ph thuc vo thng lng nh sng m n
nhn c. in trtrong ca t bo quang in rt ln v c th xc nh t dc
ca c tuyn vng bo ho:
=
aka
dV
dI1
nhy ph ca t bo quang in c biu din thng qua gi tr ca dng anottrong vng bo ho, thng vo c10 - 100 mA/W.
2.3.3. T bo quang in dng kh
T bo quang in dng kh c cu to tng t t bo quang in chn khng,
ch khc ch th tch bn trong ca n c in y bng kh, thng l kh acgon,
di p sut c10-1 - 10-2 mmHg.
K
A Ia
E
Rm
Ia (A)
Vak (V)
4,75 mW
2,37 mW
0,95 mW
4
3
2
1
0 20 40 60 80 100 120
Hnh 2.25 S t ng ng v c tr ng I - v c a t bo quang i n chn khng
a) b)
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
45/179
Khi in p thp hn 20V, c tuyn I - V c dng ging nh t bo quang in
chn khng. Khi in p cao, in t chuyn ng vi tc ln lm ion ho cc
nguyn t kh, kt qu l dng anot tng ln t 5 - 10 ln.
2.3.4. Thit b nhn quang
Khi b mt vt rn b bn ph bi cc in t c nng lng cao, n c th pht
x cc in t (gi l pht x th cp). Nu sin t pht x th cp ln hn sin
t ti th c kh nng khuch i tn hiu. S khuch i c thc hin bng cc
thit b nhn quang (hnh 2.27).
Cc in t ti (in t scp) c pht x t mt photocatot t trong chn
khng v b chiu sng. Sau chng c tiu t trn c cc th nht ca dy cc
in cc (dynode) ni tip. B mt cc in cc ni tip ph bng vt liu c kh nng
pht xin t th cp. Theo chiu i tin cc th nht n cc in cc tip theo,
in th ca cc in cc tng dn sao cho cc in t sinh ra tin cc th k s b
ht bi in cc th (k+1). Kt quin cc sau sin t ln hn in cc trc
.
0,5.10-2 lm
Hnh 2.26 c tr ng v nh y c a t bo quang i n d ng kh
Ia (A)
Vak (V)
2
1
0 20 40 60 80 100 120
10-2 lm
1,5.10-2 lm
2.10-2 lm
Vak (V)
6
2
0 20 40 60 80
4
8
nh
yt
ng
i
Hnh 2.27 Thi t b nhn quang1)b Photocatot 2) Dynode ( i n c c th c p)
K A
1
2
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
46/179
H s khuch i ca thit b nhn quang xc nh theo cng thc:
( )ntcM =
c - h s thu nhn in t hu hiu ca cc cc.t- h s chuyn ti hu hiu tin cc ny sang in cc khc.
- h s pht x th cp (sin t th cp pht ra khi c mt in tp vo in
cc).
Vi sin cc n = 5 - 15, h s pht x th cp = 5 - 10 v t > 90%, th M
~106 - 108.
Chng III
Cm bin o nhit
3.1. Khi nim cbn
Nhit l mt trong s nhng i lng c nh hng rt ln n tnh cht vtcht. Bi vy trong nghin cu khoa hc, trong cng nghip cng nh trong i sng
hng ngy vic o nhit l rt cn thit. Tuy nhin vic xc nh chnh xc mt
nhit l mt vn khng n gin. a s cc i lng vt l u c th xc nh
trc tip nhso snh chng vi mt i lng cng bn cht. Nhit l i lng ch
c tho gin tip da vo s ph thuc ca tnh cht vt liu vo nhit .
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
47/179
3.1.1. Thang o nhit
o nhit trc ht phi thit lp thang nhit . Thang nhit tuyt i
c thit lp da vo tnh cht ca kh l tng.
Theo nh l Carnot: hiu sut ca mt ng cnhit thun nghch hot ng
gia hai ngun c nhit 1 v 2 trong mt thang o bt k ch ph thuc vo 1 v2:
( )( )
2
1
F
F
= (3.1)
Dng ca hm F ph thuc vo thang o nhit . Ngc li vic chn dng hm F s
quyt nh thang o nhit . t F() = T, khi hiu sut nhit ca ng cnhit
thun nghch c vit nh sau:
2
1
TT1= (3.2)
Trong T1 v T2 l nhit ng hc tuyt i ca hai ngun.
i vi cht kh l tng, ni nng U ch ph thuc vo nhit ca cht kh v
phng trnh c trng lin h gia p sut p, th tch v v nhit c dng:
p.v=G()
C th chng minh c rng:
G()=RT
Trong R l hng s kh l tng, T l nhit ng hc tuyt i.
c th gn mt gi tr s cho T, cn phi xc nh n v cho nhit . Mun
vy ch cn gn gi tr cho nhit tng ng vi mt hin tng no vi iu kin
hin tng ny hon ton xc nh v c tnh lp li.
Thang Kelvin (Thomson Kelvin - 1852): Thang nhit ng hc tuyt i,
n v nhit l K. Trong thang o ny ngi ta gn cho nhit ca im cn bng
ba trng thi nc - nc - hi mt gi tr s bng 273,15 K.
Thang Celsius (Andreas Celsius - 1742): Thang nhit bch phn, n v
nhit l oC v mt Celsius bng mt Kelvin.
Nhit Celsius xc nh qua nhit Kelvin theo biu thc:
T(oC)= T(K) - 273,15 (3.3)
Thang Fahrenheit (Fahrenheit - 1706): n v nhit l oF. Trong thang o
ny, nhit ca im nc tan l 32oF v im nc si l 212oF.
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
48/179
Quan h gia nhit Fahrenheit v nhit Celssius:
( ) ( ){ }32FT9
5CT oo = (3.4)
( ) ( ) 32CT5
9FT oo += (3.5)
Bng 3.1 Cho cc gi tr tng ng ca mt s nhit quan trng theo cc thang o
khc nhau.
Bng 3.1
Nhi Kelvin (K) Celsius (oC) Fahrenheit (oF)
im 0 tuyt i 0 -273,15 -459,67
Hn hp nc - nc 273,15 0 32
Cn bngnc - nc - hi 273,16 0,01 32,018
Nc si 373,15 100 212
3.1.2. Nhit o c v nhit cn o
Gi s mi trng o c nhit thc bng Tx, nhng khi o ta ch nhn c
nhit Tc l nhit ca phn t cm nhn ca cm bin. Nhit Tx gi l nhit
cn o, nhit Tc gi l nhit o c. iu kin o ng nhit l phi c
s cn bng nhit gia mi trng o v cm bin. Tuy nhin, do nhiu nguyn nhn,
nhit cm bin khng bao git ti nhit mi trng Tx, do tn ti mtchnh lch nhit Tx - Tc nht nh. chnh xc ca php o ph thuc vo hiu s
Tx - Tc , hiu s ny cng b, chnh xc ca php o cng cao. Mun vy khi o cn
phi:
- Tng cnng s trao i nhit gia b cm bin v mi trng o.- Gim s trao i nhit gia b cm bin v mi trng bn ngoi.Chng ta hy kho st trng hp o bng cm bin tip xc. Lng nhit truyn
t mi trng vo b cm bin xc nh theo cng thc:( )dtTTAdQ cx =
Vi: - h s dn nhit.
A - din tch b mt trao i nhit.
T - thi gian trao i nhit.
Lng nhit cm bin hp th:
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
49/179
cmCdTdQ =
Vi: m - khi lng cm bin.
C - nhit dung ca cm bin.
Nu b qua tn tht nhit ca cm bin ra mi trng ngoi v gi , ta c:
( ) ccx mCdTdtTTA =
tng cng trao i nhit gia mi trng c nhit cn o v cm bin ta
phi dng cm bin c phn t cm nhn c t nhit thp, h s dn nhit cao, hn
ch tn tht nhit t cm bin ra ngoi th cc tip im dn t phn t cm nhn ra
mch o bn ngoi phi c h s dn nhit thp.
3.1.3. Phn loi cm bin o nhit
Cc cm bin o nhit c chia lm hai nhm:
- Cm bin tip xc: cm bin tip xc vi mi trng o, gm:+ Cm bin gin n(nhit k gin n).
+ Cm bin in tr(nhit in tr).
+ Cp nhit ngu.
- Cm bin khng tip xc: ho k.Di y nghin cu mt s loi cm bin cbn.
3.2. Nhit k gin n
Nguyn l hot ng ca nhit k gin nda vo s gin nca vt liu khi
tng nhit . Nhit k loi ny c u im kt cu n gin, d ch to.
3.2.1. Nhit k gin ndng cht rn
Thng c hai loi: gm v kim loi, kim loi v kim loi.
t =AmC
, g i l h ng s th i
gian nhi t, ta c:
=
dt
TT
dT
cx
c
Nghi m c a ph ng trnh c d ng:
=t
xc keTT Hnh 3.1. Trao i nhi t c a c m
Tx
T1
0,63Tx
t
Hnh 3.2 Nhi t k gin na) Nhi t k m - kim lo i b) Nhi t k kim lo i - kim lo i
2
1a)
1
2
b)
A
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
50/179
- Nhit k gm - kim loi(Dilatomet): gm mt thanh gm (1) t trong ngkim loi (2), mt u thanh gm lin kt vi ng kim loi, cn u A ni vi h thng
truyn ng ti b phn ch th. H s gin nnhit ca kim loi v ca gm l k v
g. Do k > g, khi nhit tng mt lng dt, thanh kim loi gin thm mt lng
dlk, thanh gm gin thm dlg vi dlk>dlg, lm cho thanh gm dch sang phi. Dch
chuyn ca thanh gm ph thuc dlk- dlg do ph thuc nhit .
- Nhit k kim loi - kim loi: gm hai thanh kim loi (1) v (2) c h s ginnnhit khc nhau lin kt vi nhau theo chiu dc. Gi s1 > 2 , khi gin nnhit
hai thanh kim loi cong v pha thanh (2). Da vo cong ca thanh kim loi xc
nh nhit .
Nhit k gin ndng cht rn thng dng o nhit di 700oC.
3.2.2. Nhit k gin ndng cht lng
Nhit k gm bnh nhit (1), ng mao dn (2) v cht lng (3). Cht lng s dng
thng dng l thu ngn c h s gin nnhit =18.10-5/oC, v nhit k bng thu
tinh c =2.10-5/oC.
Khi o nhit , bnh nhit c t tip xc vi mi trng o. Khi nhit
tng, cht lng gin nv dng ln trong ng mao dn. Thang o c chia trn
v theo dc ng mao dn.
Di nhit lm vic t - 50 600oC tu theo vt liu ch to v bc.
3.3. Nhit kin tr
3.3.1. Nguyn l
Nguyn l chung o nhi t b ng cc i n tr
l d a vo s ph thu c i n tr su t c a v t li u theo
nhi t .
Trong tr ng h p t ng qut, s thay i i n tr
theo nhi t c d ng:
( ) ( )00 TTF.RTR =
R0 l i n tr nhi t T 0, F l hm c tr ng cho
v t li u v F = 1 khi T = T0.
1
2
3
Hnh 3.3 Nhi t k gi n
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
51/179
Hin nay thng s dng ba loi in tro nhit l: in trkim loi,
in trsilic v in trch to bng hn hp cc oxyt bn dn.
Trng hp in trkim loi, hm trn c dng:
( )32
0 CTBTAT1R)T(R +++= (3.6)Trong nhit T o bng oC, T0=0
oC v A, B, C l cc h s thc nghim.
Trng hp in trl hn hp cc oxyt bn dn:
=
0
0T
1
T
1Bexp.R)T(R (3.7)
T l nhit tuyt i, B l h s thc nghim.
Cc h sc xc nh chnh xc bng thc nghim khi o nhng nhit
bit trc. Khi bit gi tr cc h s, t gi tr ca R ngi ta xc nh c nhit cn o.
Khi bin thin ca nhit T (xung quanh gi tr T) nh, in trc th coi
nh thay i theo hm tuyn tnh:
( ) ( )( )T1TRTTR R +=+ (3.8)
Trong :
( ) dT
dR
TR
1R = (3.9)
c gi h s nhit ca in trhay cn gi l nhy nhit nhit T. nhy
nhit ph thuc vo vt liu v nhit , v d0oC platin (Pt) c R=3,9.10-3/oC.
Cht lng thit bo xc nh gi tr nh nht m n c tho cmin0
R
R, do
cng xc nh s thay i nh nht ca nhit c th pht hin c:
minoR
min
R
R1T
=
V d nu 6
min0
10R
R =
v vi nhng php o quanh im 0oC, vt liu l platin th
4min 10.6,2T
= oC.
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
52/179
Thc ra, in trkhng ch thay i khi nhit thay i do s thay i in tr
sut m cn chu tc ng ca s thay i kch thc hnh hc ca n. Bi vy i vi
mt in trdy c chiu di l v tit din s, h s nhit c dng:
dT
ds
s
1
dT
dl
l
1
dT
d1
dT
dR
R
1R +
==
t:dT
d1
= ;dT
dl
l
1l = ;
dT
ds
s
1s =
slR +=
Vi ls 2= ta c: lR =
Trn thc t thng l>> nn c th coi = R .
3.3.2. Nhit kin trkim loi
a) Vt liuYu cu chung i vi vt liu lm in tr:
-C in trsut ln in trban u R0 ln m kch thc nhit k vnnh.
-H s nhit in trca n tt nht l lun lun khng i du, khng trit tiu.-C bn c, ho nhit lm vic.-D gia cng v c kh nng thay ln.
Cc cm bin nhit thng c ch to bng Pt v Ni. Ngoi ra cn dng Cu, W.- Platin :
+ C th ch to vi tinh khit rt cao (99,999%) do tng chnh xc
ca cc tnh cht in.
+ C tnh trv mt ho hc v tnh n nh cu trc tinh th cao do m bo
tnh n nh cao v cc c tnh dn in trong qu trnh s dng.
+ H s nhit in tr0oC bng 3,9.10-3/oC.
+ in tr100oC ln gp 1,385 ln so vi 0oC.
+ Di nhit lm vic kh rng t -200oC 1000oC.
- Nikel:+ C nhy nhit cao, bng 4,7.10-3/oC.
+ in tr100oC ln gp 1,617 ln so vi 0oC.
+ D b oxy ho khi nhit cao lm gim tnh n nh.
+ Di nhit lm vic thp hn 250oC.
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
53/179
ng c s dng trong mt s trng hp nh tuyn tnh cao ca in tr
theo nhit . Tuy nhin, hot tnh ho hc ca ng cao nn nhit lm vic thng
khng vt qu 180oC. in trsut ca ng nh, do ch to in trc in
trln phi tng chiu di dy lm tng kch thc in tr.
Wonfram c nhy nhit v tuyn tnh cao hn platin, c th lm vic
nhit cao hn. Wonfram c th ch to dng si rt mnh nn c th ch to c
cc in trcao vi kch thc nh. Tuy nhin, ng sut d sau khi ko si kh b trit
tiu hon ton bng cch do gim tnh n nh ca in tr.
Bng 3.2
Thng s Cu Ni Pt W
Tf(oC) 1083 1453 1769 3380
c (JoC-1kg-1) 400 450 135 125
(WoC-1m-1) 400 90 73 120
l x106 (oC) 16,7 12,8 8,9 6
x108 (m) 1,72 10 10,6 5,52
x103 (oC-1) 3,9 4,7 3,9 4,5
b) Cu to nhit kin tr
trnh s lm nng u o dng in chy qua in trthng gii hn gi
tr mt vi mA v in tr c nhy nhit cao th in trphi c gi tr ln.
Mun vy phi gim tit din dy hoc tng chiu di dy. Tuy nhin khi gim tit
din dy bn li thp, dy in trd bt, vic tng chiu di dy li lm tng
kch thc in tr. hp l ngi ta thng chn in trR0oC c gi tr vo
khong 100, khi vi in trplatin s c ng knh dy cvi m v chiu di
khong 10cm, sau khi qun li s nhn c nhit k c chiu di c1cm. Cc sn
phm thng mi thng c in tr0oC l 50, 500 v 1000, cc in trln
thng c dng o di nhit thp.
-Nhit kcng nghip: s dng cho mc ch cng nghip, cc nhit k phi c v
bc tt chng c va chm mnh v rung ng, in trkim loi c cun v bao
bc trong thu tinh hoc gm v t trong v bo v bng thp. Trn hnh 3.4 l cc
nhit k dng trong cng nghip bng in trkim loi platin.
81 2 3
45
1
7
6
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
54/179
- Nhit kbmt:
Nhit k b mt dng o nhit trn b mt ca vt rn. Chng thng c
ch to bng phng php quang ho v s dng vt liu lm in tr l Ni, Fe-Ni
hoc Pt. Cu trc ca mt nhit k b mt c dng nh hnh v 3.5. Chiu dy lp kim
loi cvi m v kch thc nhit k c1cm2.
c trng chnh ca nhit k b mt:
- nhy nhit : ~5.10-3/oC i vi trng hp Ni v Fe-Ni
~4.10-3/oC i vi trng hp Pt.
- Di nhit s dng: -195oC 260 oC i vi Ni v Fe-Ni.
-260oC 1400 oC i vi Pt.
Khi s dng nhit k b mt cn c bit lu n nh hng bin dng ca bmt o.
3.3.3. Nhit kin trsilic
Silic tinh khit hoc n tinh th silic c h s nhit in trm, tuy nhin khi
c kch tp loi n th trong khong nhit thp chng li c h s nhit in tr
dng, h s nhit in tr~0,7%/oC 25oC. Phn t cm nhn nhit ca cm bin
2200
2400R()
Hnh 3.5 Nhi t k b m t
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
55/179
silic c ch to c kch thc 500x500x240 m c m kim loi mt pha cn
pha kia l b mt tip xc.
3.3.4. Nhit kin troxyt bn dn
a) Vt liu ch to
Nhit in tr c ch to t hn hp oxyt bn dn a tinh th nh: MgO,
MgAl2O4, Mn2O3, Fe3O4, Co2O3, NiO, ZnTiO4.
S ph thuc ca in trca nhit in trtheo nhit cho bi biu thc:
=
0
2
0
0T
1
T
1exp
T
TR)T(R (3.11)
Trong R0() l in trnhit T0(K).
nhy nhit c dng:
2R T
b+=
V nh hng ca hm mn in trchim u th nn biu thc (3.11) c th vit
li:
= 00 T
1
T
1
BexpR)T(R (3.12)
V nhy nhit:
2R T
B=
Vi B c gi tr trong khong 3.000 - 5.000K.
b) Cu to
Trong d i nhi t lm vi c ( -55
200oC) c th l y g n ng gi tr i n tr
c a c m bi n theo nhi t theo cng th c:
( ) ( )2000T TTBTTA1RR ++=
Trong R0 v T0 l i n tr v nhi t
tuy t i i m chu n.
S thay i nhi t c a i n tr t ng
i nh nn c th tuy n tnh ho b ng
cch m c thm m t i n tr ph .
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
56/179
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
57/179
Tng t ti mt tip xc u t do (nhit t0) cng xut hin mt hiu in
th eAB(t0).
Gia hai u ca mt dy dn cng c chnh lch nng in t t do, do
cng c s khuch tn in t v hnh thnh hiu in th tng ng trong A l
eA(t,t0) v trong B l eB(t,t0).
Sc in ng tng sinh ra do hiu ng nhit in xc nh bi cng thc sau:
)t,t(e)t,t(e)t(e)t(eE 0B0A0BAABAB +++= (3.13)
V eA(t0,t) v eB(t,t0) nh v ngc chiu nhau c th b qua, nn ta c:
)t(e)t(eE 0BAABAB +=
Nu nhit hai mi hn bng nhau, chng hn bng t0 khi sc in ng tng:
0)t(e)t(eE 0BA0ABAB =+=
Hay:)t(e)t(e 0AB0BA = (3.14)
Nh vy:
)t(e)t(eE 0ABABAB = (3.15)
Phng trnh (3.15) gi l phng trnh cbn ca cp nhit ngu. T phng trnh
(3.15) nhn thy nu gi nhit t0 = const th:
)t(fC)t(eE ABAB =+= (3.16)
Chn nhit mt mi hn t0 = const bit trc lm nhit so snh v o sc in
ng sinh ra trong mch ta c th xc nh c nhit t mi hn th hai.
Sc in ng ca cp nhit khng thay i nu chng ta ni thm vo mch mt
dy dn th ba (hnh 3.9) nu nhit hai u ni ca dy th ba ging nhau.
Tht vy:
- Trong trng hp a:)t(e)t(e)t(e)t,t(E 0CA0BCAB0ABC ++=
V:
0)t(e)t(e)t(e 0CA0BC0AB =++
Nn:
)t(e)t(e)t,t(E 0ABAB0ABC =
2 3t0t0
A B
C
2
3
t0
t1
C4
B
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
58/179
- Trng hp b:)t(e)t(e)t(e)t(e)t,t,t(E 1CB1BC0ABAB01ABC ++=
V:
)t(e)t(e1CB1BC
=
Nn:
)t(e)t(e)t,t(E 0ABAB0ABC =
Nu nhit hai u ni khc nhau s lm xut hin sc in ng k sinh.
3.4.2. Cu to cp nhit
a) Vt liu ch to
ch to cc nhit in c th dng nhiu kim loi v hp kim khc nhau.
Tuy nhin chng phi m bo cc yu cu sau:
- Sc in ng ln ( d dng ch to dng co th cp).- C bn chc v ho hc nhit lm vic.- D ko si.- C kh nng thay ln.- Gi thnh r.
Hnh 3.10 biu din quan h gia sc in ng v nhit ca cc vt liu dng
ch to in cc so vi in cc chun platin.
21
3
8
910
54
6
7
11
T
Ed
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
59/179
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
60/179
b) Cu to
Cu to in hnh ca mt cp nhit cng nghip trnh by trn hnh 3.12.
u lm vic ca cc in cc (3) c hn ni vi nhau bng hn vy, hn kh
hoc hn bng tia in t. u t do ni vi dy ni (7) ti dng co nhcc vt ni
(6) dy t trong u ni dy (8). cch ly cc in cc ngi ta dng cc ng s
cch in (4), s cch in phi trv ho hc v bn cv nhit nhit lm
vic. bo v cc in cc, cc cp nhit c v bo v (1) lm bng s chu nhit
hoc thp chu nhit. H thng v bo v phi c nhit dung nh gim bt quntnh nhit v vt liu ch to v phi c dn nhit khng qu nh nhng cng khng
c qu ln. Trng hp v bng thp mi hn u lm vic c th tip xc vi v
gim thi gian hi p.
3.4.3. Mch o v dng c thcp
Hnh 3.12 C u t o c p nhi t1) V b o v 2) M i hn 3) Dy i n c c 4) S cch i n
5) B ph n l p t 6) Vt n i dy 7) Dy n i 8) u n i dy
1
324 5 6
7
8
Hnh 3.11 S c i n ng c a m t s c p nhi t ng uE-Chromel/Constantan R- Platin-Rodi (13%)/PlatinJ- S t/Constantan S- Platin-Rodi (10%)/PlatinK- Chromel/Alumel B-Platin-rodi 30% / Platin-rodi 6%
E
J
K
R
S
B
toC
E
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
61/179
Nhit cn o c xc nh thng qua vic o sc in ng sinh ra hai
u dy ca cp nhit ngu. chnh xc ca php o sc in ng ca cp nhit
ngu ph thuc nhiu yu t. Mun nng cao chnh xc cn phi:
- Gim thiu nh hng ca tc ng ca mi trng o ln nhit u t do.- Gim thiu s st p do c dng in chy qua cc phn t ca cm bin v mcho.
a) S mch o dng milivn k
- S:
Trn hnh 3.13 biu din so thng dng s dng milivn k tin.
Khi nhit hai u t do (2) v (3) bng nhau th sc in ng trong mch
chnh l sc in ng ca cp nhit, nu chng khc nhau th trong mch xut hin
sut in ng k sinh cc mi ni v lm sai lch kt quo.
o trc tip hiu nhit gia hai im ngi ta dng so vi sai nh
hnh 3.14.
Trong s ny, c hai u 1 v 2 ca cp nhit l u lm vic tng ng vi
nhit t1 v t2. Kt quo cho php ta xc nh trc tip gi tr ca hiu s hai nhit
t1- t2.
1
2 3
t
t0 t0
A B
C
Hnh 3.13 S m ch o
m
1 2t1 t2
3 4t0 t0
Hnh3.14 S o vi sai
A AB
mV
)t,t(E '0AB
)t,t(E 0'0AB
Hnh 3.16 Hi u ch nhnhi t u t do
A A A AB B B B
Hnh 3.15 S m c n i ti p
mV
toC
E
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
62/179
Trng hp nhit mi trng o khng khc nhiu nhit u t do, tng
nhy php o c th mc theo s ni tip n cp nhit nh hnh 3.15. Sc in
ng tng ca b mc ni tip bng )t,t(nE 0AB .
- B nhit u tdo:
Thng thng cp nhit ngu c chun vi t0 = 0oC ng vi:
)t(e)t(e)t,t(E 0ABAB0AB =
Nu nhit u t do bng 0t '0 th gi tr sc in ng o c:
)t(e)t(e)t,t(E '0ABAB'0AB =
Rt ra:
[ ])t(e)t(e)t,t(E)t,t(E 0AB'0AB'0AB0AB +=
Hay:
)t,t(E)t,t(E)t,t(E 0'0Ab
'0AB0AB +=
Gi tr )t,t(E '0AB l lng hiu chnh xc nh t thang chia ca cp nhit ngu
dng theo gi tro nhit u t do t
0.Di y trnh by mt s phng php b nhit u t do.
- Dng dy b: loi trnh hng ca nhit i tng o ln u t do c th mc dng
co theo s hnh 3.17.
)t(e)t(e)t(e)t(eE 0CD'0BD
'0CAAB +=
Chn dy dn C v D sao cho )t(e)t(e '0DB'0CA = ( 3412 = ), khi :
)t(e)t(eE 0CDAB = V e(t0) = 0, nn:
)t(e)t(eE 0ABAB =
C
2 3t0 t0
t0
t0
D1
C
A
E
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
63/179
- Dng cu b:Trn hnh 3.18 gii thiu s dng cu b tng nhit u t do.
Cu b gm in trR1, R2, R3 lm bng manganin (hp kim cha 99,4%Cu,
0,6%Ni) c h s nhit in trbng khng, cn R lm bng ng c h s nhit in
tr4,25 4,28.10-3oC-1 . Khi nhit u t do t0 = 0, cu cn bng UAB=0. Gi s
nhit u t do tng ln t0, khi R tng ln lm xut hin mt in p Uc.
Ngi ta tnh ton sao cho in p ny b vo sc in ng nhit mt lng ng
bng lng cn hiu chnh, ngha l Uc= EAB(t0,t0). Nh vy trn ca vo ca dng
co c in p:
)t,t(EU)t,t(E 0ABcd'0AB =+
Sai s b ca cu tiu chun khi nhit t0 thay i trong khong 0 - 50oC l 3oC.
- nh hng ca in trmch o:
Xt mch o dng milivn kin t (hnh 3.19).
t0
B ngu n
Hnh 3.18 C u b nhi t u t do
Rd R1
R2 R3
F
D
C
mV
t1t1
t0
A Bt
Hnh 3.17 B nhi t u t do b ng dy b
1t
A B 2
3
4
D
B
t0
Rd2 3
t1 t1
A B
t0
t0
Rt
RV
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
64/179
Gi: Rt l in trca cp nhit.
Rd l in trdy ni.
Rv l in trtrong ca milivn k.
Khi in p gi hai u milivn k xc nh bi cng thc:
Vdt
V0ABm
RRR
R)t,t(EV
++=
Rt ra:
++=
V
dtm0AB
R
RR1V)t,t(E (3.17)
Theo biu thc (3.17) khi Rv >> Rt+Rd th:
m0AB V)t,t(E
- nh hng ca Rt: i vi cp cromen/alumen hoc cp cromen/coben c in trRt kh nh nn s thay i ca n t nh hng ti kt quo. i vi cp PtRd - Pt c
in trRt kh ln (~ 15) nn s thay i ca n nh hng ng k ti kt quo.
- nh hng ca Rd: thng thng Rd kh nh nn t nh hng ti kt quo.- nh hng ca RV: Rv = Rkd + Rf.
in tr ph Rf ca milivn k thng ch to bng vt liu c R = 0 nn
khng nh hng, s thay i Rv khi nhit tng ch yu do s thay i ca in tr
khung dy Rkd (ch to bng ng R = 4,2.10-3/oC). gim sai s nn chn RP/Rkd
ln.
b) S mch o xung i dng in th k
Trn hnh 3.20 trnh by so bng phng php xung i, da theo nguyn
tc so snh in p cn o vi mt in p ri trn mt on in tr.
Hnh 3.19 nh h ng c a i n tr m ch o
1t
G
K D
EX
E
EMP
R
GEX Rd
RGiP
i0iC A B
R c
E
Rx
RR
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
65/179
Theo s hnh (3.20a) ta c:
)RRR(IRIE GxdPABCX +++=
P0C III +=
)RRR(IR)II(E GxdPABP0X ++++=
GXdAB
AB0XP
RRRR
RIEI
+++
=
Nu EX = I0RAB th IP = 0, tc l in th k ch khng, khi in p ri trn AB
bng gi tr EX cn o.
Ta c:
RL
lR AB =
RL
lIE 0X =
Nu cnh c I0, L, R ta c Ex ph thuc n tr vo l tc l ph thuc vo v tr
con chy ca ng ho.
Trn s hnh (3.20b), EM l mt pin mu, RM l mt in tr mu bng
manganin. Khi ng P vo K th in p ri trn RMc so snh vi pin mu. Nu
kim in k ch khng th khng cn iu chnh dng I0, nu kim in k lch khi
khng th dch chuyn Rc kim in k v khng. Khi o ng P vo D v x dch
bin trR kim in k ch khng, khi Ex = UAB.
3.5. Ho k
Cc cm bin quang thuc loi cm bin o nhit khng tip xc, gm: ho k
bc x ton phn, ho k quang hc.
3.5.1. Ho k bc x ton phn
Nguyn l da trn nh lut: Nng lng bc x ton phn ca vt en tuyt i
t l vi lu tha bc 4 ca nhit tuyt i ca vt.
t
- +
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
66/179
4TE = (3.18)
Trong : l hng s, T l nhit tuyt i ca vt en tuyt i (K).
Thng thng c hai loi: ho k bc x c ng knh hi t, ho k bc x c knh
phn x.
Trong s hnh (3.21a): nh sng t ngun bc x (1) qua thu knh hi t (2)
p ti b phn thu nng lng tia bc x (4), b phn ny c ni vi dng co
th cp (5).
Trong s hnh (3.21b): nh sng t ngun bc x (1) p ti gng phn x
(3) v hi t ti b phn thu nng lng tia bc x (4), b phn ny c ni vi dng
co th cp (5).
B phn thu nng lngc th l mt vi nhit kin trhoc l mt t hp cp
nhit, chng phi tho mn cc yu cu:
+ C th lm vic bnh thng trong khong nhit 100 - 150oC.
+ Phi c qun tnh nhit nh v n nh sau 3 - 5 giy.
+ Kch thc nh tp trung nng lng bc x vo o.
Trn hnh 3.22 trnh by c u
t o c a m t b thu l t h p c p nhi t.
Cc c p nhi t (1) th ng dng c p
crmen/cben m c n i ti p v i nhau.
Cc v t en (2) ph b ng b t platin.
Ho k dng g ng ph n x t n
th t n ng l ng th p ( ~ 10%), ho k
dng th u knh h i t c th t n th t Hnh 3.22 B thu n ng l ng1) C p nhi t 2)L p ph platin
1
2
5 5
Hnh 3.21 Ho k b c x ton ph na) Lo i c ng knh h i t b) Lo i c knh ph n x
1) Ngu n b c x 2) Th u knh h i t 3) G ng ph n x4) B phn thu n ng l ng 5) D ng c o th c p
12
4
a) b)
1
34
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
67/179
30 - 40%. Tuy nhin loi th nht li
c nhc im l khi mi trng nhiu bi, gng b bn, phn x gim do tng
sai s.
Khi o nhit bng ho k bc x sai s thng khng vt qu 27oC, trong
iu kin:
+ Vt o phi c den xp x bng 1.
+ T l gia ng knh vt bc x v khong cch o (D/L) khng nh hn
1/16.
+ Nhit mi trng 20 2oC.
Khong cch o tt nht l 1 0,2 mt.
3.5.2. Ho k quang in
Ho k quang in ch to da trn nh lut Plng:
=
1e
CI
RT
C
5
1
2T
(3.19)
Trong l bc sng, C1, C2 l cc hng s.
Trong th c t en c a v t o
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
68/179
Khi o, hng ho k vo vt cn o, nh sng t vt bc x cn o nhit (1)
qua vt knh (2), knh lc (3), v cc vch ngn (4), (6), knh lc nh snh (7) ti th
knh (8) v mt. Bt cng tc K cp in nung nng dy tc bng n mu (5), iu
chnh bin trRb sng ca dy tc bng n trng vi sng ca vt cn o.
Sai s khi o:
Sai s do en ca vt o < 1. Khi To xc nh bi cng thc:
=1
lnCT
1
2do
Cng thc hiu chnh: To = Tc + T
Gi tr ca T cho theo th.
Ngoi ra sai s ca php o cn do nh hng ca khong cch o, tuy nhin sai
s ny thng nh. Khi mi trng c bi lm bn ng knh, kt quo cng bnh
hng.
mA
1 2 34
5 78
Rb
Hnh 3.25 S ho k quang h c1) Ngu n b c x 2)V t knh 3) Knh l c 4&6) Thnh ng n
5) Bng n m u 7) Knh l c nh sng 8) Th knh
6
K
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
69/179
Chng IV
Cm bin o v tr v dch chuyn
4.1. Nguyn l o v tr v dch chuyn
Vic xc nh v tr v dch chuyn ng vai tr rt quan trng trong k thut.
Hin nay c hai phng php cbn xc nh v tr v dch chuyn.Trong phng php th nht, b cm bin cung cp tn hiu l hm ph thuc
vo v tr ca mt trong cc phn t ca cm bin, ng thi phn t ny c lin quan
n vt cn xc nh dch chuyn.
Trong phng php th hai, ng vi mt dch chuyn cbn, cm bin pht ra
mt xung. Vic xc nh v tr v dch chuyn c tin hnh bng cch m s xung
pht ra.
Mt s cm bin khng i hi lin kt chc gia cm bin v vt cn o v tr
hoc dch chuyn. Mi lin h gia vt dch chuyn v cm bin c thc hin thng
qua vai tr trung gian ca in trng, t trng hoc in t trng, nh sng.
Trong chng ny trnh by cc loi cm bin thng dng dng xc nh v tr
v dch chuyn ca vt nhin th kin tr, cm bin in cm, cm bin in
dung, cm bin quang, cm bin dng sng n hi.
4.2. in th kin tr
Loi cm bin ny c cu to n gin, tn hiu o ln v khng i hi mch
in c bit x l tn hiu. Tuy nhin vi cc in th kin trc con chy c
hc c s c xt gy n v mn, s ln s dng thp v chu nh hng ln ca mi
trng khi c bi v m.
4.2.1. in th k dng con chy chc
a) Cu to v nguyn l lm vic
Cm bin gm mt in trcnh Rn, trn c mt tip xc in c th di
chuyn c gi l con chy. Con chy c lin kt chc vi vt chuyn ng cn
kho st. Gi tr ca in trRx gia con chy v mt u ca in trRn l hm phthuc vo v tr con chy, cng chnh l v tr ca vt chuyn ng.
- i vi in th k chuyn ng thng (hnh 4.1a):nx R
L
lR =
(4.1)
- Trng hp in th k dch chuyn trn hoc xon:
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
70/179
n
M
x RR
=
(4.2)
Trong M < 360o khi dch chuyn trn (hnh 4.1b) v M > 360
o khi dch chuyn
xon. (hnh 4.1c)
Cc in trc ch to c dng cun dy hoc bng dn.
Cc in trdng cun dy thng c ch to t cc hp kim Ni - Cr, Ni - Cu, Ni - Cr - Fe, Ag - Pd qun thnh vng xon dng l xo trn li cch in (bng thu
tinh, gm hoc nha), gia cc vng dy cch in bng emay hoc lp oxyt b mt.
Cc in trdng bng dn c ch to bng cht do trn bt dn in l
cacbon hoc kim loi cht ~10-2m.
Cc in trc ch to vi cc gi tr Rn nm trong khong 1kn 100k,
i khi t ti M.
Cc con chy phi m bo tip xc in tt, in tr tip xc phi nh v nnh.
b) Cc c trng
- Khong chy c ch ca con chy:
Rn, , L
Rx, l
RRn
Rn
R
Hnh 4.1 Cc d ng i n th k1) i n tr 2) Con ch y
a)
b) c)
12
1
1
21
2
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
71/179
Thng thng u hoc cui ng chy ca con chy t s Rx/Rn khng n
nh. Khong chy c ch l khong thay i ca x m trong khong Rx l hm
tuyn tnh ca dch chuyn.
- Nng sut phn gii:
i vi in trdy cun, phn gii xc nh bi lng dch chuyn cc i
cn thit a con chy t v tr tip xc hin ti sang v tr tip xc ln cn tip
theo. Gi s cun dy c n vng dy, c th phn bit 2n-2 v tr khc nhau vin ca
con chy:
+ n v tr tip xc vi mt vng dy.
+ n - 2 v tr tip xc vi hai vng dy.
phn gii ca in trdng dy ph thuc vo hnh dng v ng knh ca
dy in trv vo khong ~10m.
phn gii ca cc in tr kiu bng dn ph thuc vo kch thc ht,
thng vo c~ 0,1 m.
- Thi gian sng:
Thi gian sng ca in k l s ln s dng ca in th k. Nguyn nhn gy
ra h hng v hn ch thi gian sng ca in th k l s mi mn con chy v dyin trtrong qu trnh lm vic. Thng thi gian sng ca in th k dng dy dn
vo c106 ln, in k dng bng dn vo c5.107 - 108 ln.
4.2.2. in th k khng dng con chy chc
khc phc nhc im ca in th k dng con chy c hc, ngi ta s
dng in th k lin kt quang hoc t.
Kho ng ch y c
Cu i ng ch y
u ng ch y x
Hnh 4.2 S ph thu c c a i n
tr i n th k vo v tr con ch y
Rx
Hnh 4.3 phn gi i c a i n th
k d ng dy
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
72/179
a) in th k dng con tr quang
Hnh 4.4 trnh by s nguyn l ca mt in th k dng con tr quang.
in th k trn dng con tr quang gm iot pht quang (1), bng o (2), bng
tip xc (3) v bng quang dn (4). Bng in tro c phn cch vi bng tip xc
bi mt bng quang dn rt mnh lm bng CdSe trn c con tr quang dch
chuyn khi trc ca in th k quay. in trca vng quang dn gim ng k trong
vng c chiu sng to nn s lin kt gia bng o v bng tip xc.
Thi gian hi p ca vt liu quang dn cvi chc ms.
b) in th k dng con tr t
Hnh 4.5 trnh by s nguyn l mt in th k t gm hai tin trR1 v
R2 mc ni tip v mt nam chm vnh cu (gn vi trc quay ca in th k) bao
ph ln mt phn ca in trR1 v R2, v tr phn b bao ph ph thuc gc quay catrc.
in p ngun ESc t gia hai im (1) v (3), in p o Vm ly tim
chung (2) v mt trong hai u (1) hoc (3).
Khi in p o c xc nh bi cng thc:
Hnh 4.4 i n th k quay dng con tr quang1) iot pht quang 2) B ng o 3) B ng ti p xc 4) B ng quang d n
i n tr
Th i gian
1
2
3 4
~20 ms
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
73/179
S1
S
21
1m E
R
RE
RR
RV =
+=
(4.3)
Trong R1 l hm ph thuc v tr ca trc quay, v tr ny xc nh phn ca R1 chu
nh hng ca t trng cn R = R1
+ R2
= const.
T hnh 4.5b ta nhn thy in p o ch tuyn tnh trong mt khong ~90oi
vi in k quay. i vi in k dch chuyn thng khong tuyn tnh ch cvi
mm.
4.3. Cm bin in cm
Cm bin in cm l nhm cc cm bin lm vic da trn nguyn l cm ng
in t. Vt cn o v tr hoc dch chuyn c gn vo mt phn t ca mch t gy
nn s bin thin t thng qua cun o. Cm bin in cm c chia ra: cm bin t
cm v h cm.
4.3.1. Cm bin tcm
a) Cm bin tcm c khe tbin thin
- Cm bin t cm n: trn hnh 4.6 trnh by s nguyn l cu to ca mts loi cm bin t cm n.
Hnh 4.6 C m bi n t c m1) Li s t t 2) Cu n dy 3) Ph n ng
XV XV
a) b) c)
1
2
3 12
31
2
R
R2R1
1
2
3
Hnh 4.5 i n th k i n t
30%
50%
70%
0O 180O 360O
Vm/ES
a) b)
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
74/179
Cm bin t cm n gm mt cun dy qun trn li thp c nh
(phn tnh) v mt li thp c th di ng di tc ng ca i lng o (phn ng),
gia phn tnh v phn ng c khe hkhng kh to nn mt mch t h.
S hnh 4.6a: di tc ng ca i lng o XV, phn ng ca cm
bin di chuyn, khe hkhng kh trong mch t thay i, lm cho t trca mch t
bin thin, do h s t cm v tng trca cun dy thay i theo.
S hnh 4.6b: khi phn ng quay, tit din khe hkhng kh thay i,
lm cho t trca mch t bin thin, do h s t cm v tng trca cun dy
thay i theo.
H s t cm ca cun dy cng c th thay i do thay i tn hao sinh
ra bi dng in xoy khi tm st t dch chuyn di tc ng ca i lng o Xv
(hnh 4.6c).
Nu b qua in trca cun dy v t trca li thp ta c:
==
sW
R
WL 0
22
Trong :
W- s vng dy.
sR
0
= - t trca khe hkhng kh.
- chiu di khe hkhng kh.
s - tit din thc ca khe hkhng kh.
Trng hp W = const ta c:
+
= dL
dss
LdL
Vi lng thay i hu hn v s ta c:
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
75/179
( )
+
=
20
002
0
02 sW
sW
L
(4.4)
nhy ca cm bin t cm khi khe hkhng kh thay i (s=const):
2
0
0
0
1
LLS
+
==
(4.5)
nhy ca cm bin t cm khi thay i tit din khng kh ( = const):
0
0s
s
L
s
LS =
=
(4.6)
Tng trca cm bin:
==sW
LZ 02
(4.7)
T cng thc (4.7) ta thy tng trZ ca cm bin l hm tuyn tnh vi tit din khe
hkhng kh s v phi tuyn vi chiu di khe hkhng kh .
c tnh ca cm bin t cm n Z = f() l hm phi tuyn v ph thuc tn s
ngun kch thch, tn s ngun kch thch cng cao th nhy ca cm bin cng cao
(hnh 4.7).
L = f()
Z = f()
Z500Hz = f()
Hnh 4.7 S ph thu c gi a L, Z v i chi u dy khe h khng kh
Z, L
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
76/179
- Cm bin t cm kp lp theo kiu vi sai: tng nhy ca cm bin v tng
on c tnh tuyn tnh ngi ta thng dng cm bin t cm kp mc theo kiu vi
sai (hnh 4.8).
c tnh ca cm bin t cm kp vi sai c dng nh hnh 4.9.
b) Cm bin tcm c li tdi ng
Cm bin gm mt cun dy bn trong c li t di ng c (hnh 4.10).
XV
XV
XV
a) b) c)
Hnh 4.8 C m bi n t c m kp m c theo ki u vi sai
L = f
Hnh 4.9 c tnh c a c m bi n t c m kp l p vi sai
L1 - L2 = f()
L2 = f()
L
Hnh 4.10 S nguyn l c m bi n t c m c li t1) Cu n dy 2) Li t
l0 lf
l
XV
12
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
77/179
Di tc ng ca i lng o XV, li t dch chuyn lm cho di lf
ca li t nm trong cun dy thay i, ko theo s thay i h s t cm L ca cun
dy. S ph thuc ca L vo lf l hm khng tuyn tnh, tuy nhin c th ci thin
bng cch ghp hai cun dy ng dng vo hai nhnh k st nhau ca mt cu in
trc chung mt li st.
4.3.2. Cm bin h cm
Cu to ca cm bin h cm tng t cm bin t cm ch khc ch c thm
mt cun dy o (hnh 4.11).
Trong cc cm bin n khi chiu di khe hkhng kh (hnh 4.11a) hoc tit
din khe khng kh thay i (hnh 4.11b) hoc tn hao do dng in xoy thay i
(hnh 4.11c) s lm cho t thng ca mch t bin thin ko theo sut in ng e
trong cun o thay i.
- Cm bin n c khe hkhng kh:
T thng tc thi:
==
siW
R
iW 011t
i - gi tr dng in tc thi trong cun dy kch thch W1.
Hnh 4.11 C m bi n h c m1) Cu n s c p 2) Gng t 3) li t di ng 4) Cu n th c p (cu n o)
a)
3
XV
1
2
~
b)
1 2
3
c)
XV
3
4
~
XV
4
~
1 2
d)
XV
~~
e)
~
XV
~
)
44
1
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
78/179
Sc in ng cm ng trong cun dy o W2:
dt
di.
sWW
dt
dWe 012t2
=
=
W2 - s vng dy ca cun dy o.
Khi lm vic vi dng xoay chiu tsinIi m = , ta c:
tcosIsWW
e m012
=
v gi tr hiu dng ca sut in ng:
=
=s
kIsWW
E 012
I - gi tr hiu dng ca dng in, IWWk 012 = .
Vi cc gi tr W2, W1, 0, v I l hng s, ta c:
+
= dE
dss
EdE
Hay( )200
kss
kE+
=
(4.8)
nhy ca cm bin vi s thay i ca chiu di khe hkhng kh (s = const):
2
0
0
0
2
0
20 1
E
1
ksES
+
=
+
=
=
(4.9)
Cn nhy khi tit din khe hkhng kh s thay i ( = const):
0
0
0
Ss
Ek
s
ES =
=
=
(4.10)
0
00
ksE
= - sc in ng h cm ban u trong cun o W2 khi XV = 0.
Ta nhn thy cng thc xc nh nhy ca cm bin h cm c dng tng t
nh cm bin t cm ch khc nhau gi tr ca E0 v L0. nhy ca cm bin h
cm S v SS cng tng khi tn s ngun cung cp tng.
-
7/30/2019 GT Cam Bien Dien Cong Nghiep
79/179
- Cm bin vi sai: tng nhy v tuyn tnh ca c tnh cm bin ngi ta
mc cm bin theo s vi sai (hnh 4.11d,,e). Khi mc vi sai nhy ca cm bin
tng gp i v phm vi lm vic tuyn tnh mrng ng k.
- Bin th vi sai c li t: gm bn cun dy ghp ng trc to thnh hai cm bin
n i xng, bn trong c li t di ng c (hnh 4.12). Cc cun th cp c ni
ngc vi nhau sao cho sut in ng trong chng trit tiu ln nhau.
V nguyn tc, khi li tv tr trung gian, in p o Vmu ra hai cun th
cp bng khng. Khi li t dch chuyn, lm thay i mi quan h gia cun scp
vi cc cun th cp, tc l lm thay i h s h cm gia cun scp vi cc cun
th cp. Khi in trca thit bo ln, in p o Vm gn nh tuyn tnh vi hiu
s cc h s h cm ca hai cun th cp.4.4. Cm bin in dung
4.4.1. Cm bin tin n
Cc cm bin tin n l mt tin phng hoc hnh tr c mt bn cc gn
cnh (bn cc tnh) v mt bn cc di chuyn (bn cc ng) lin kt vi vt cn
o. Khi bn cc ng di chuyn s ko theo s thay i in dung ca tin.
- i vi cm bin h