thiết bị và hệ thống tự động

8/13/2019 Thit b v h thng t ng

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TTHHII

IIUU

IIHKK

BI

TTIILLIIUUMMNN

BB&&HHTTHH

KKHHIINNTT

LLUUHHNNHHNNIIBB22001122

CCCCNNGGNNGGHHIIPPTTPP..HHOOAACCNNGGNNGGHHIINNTT

--------------------------------------------------------

SON: TRN VN H

NNGG

NNGG

MM

G


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MC LC

Chng 1 CC KHI NIM CHUNG

1.1 Khi nim v phn loi h thng iu khin t ng............................... 11.2 Cc thnh phn ca h thng iu khin t ng...................................... 21.3 Cc v d v h thng iu khin t ng................................................ 12

Chng 2 CM BIN V CHUYN I

2.1 Gii thiu ....................................................................................................... 212.2 ng cong chun ca cm bin .................................................................. 222.3 Cc c trng c bn ca cm bin.................................................................... 242.4 Nguyn l ch to cm bin................................................................................ 282.5 Phn loi cm bin................................................................................................ 332.6 Mch o cm bin ......................................................................................... 372.7 Cm bin tim cn (Proximity Sensor) ......................................................... 412.8 Cm bin v tr v khong cch (Sensors for distance and displacement) .. 1202.9 Cm bin lc v p sut (Sensors for force and pressure) .......................... 1672.10Cm bin nhit (Temperature Sensors) .................................................. 198

Chng 3 THIT B CNG SUT V CHP HNH

3.1 Gii thiu ..................................................................................................... 2393.2 Thit b in t ............................................................................................ 2393.3 Thit b in t ............................................................................................ 2473.4 ng c in ............................................................................................... 2643.5 Thit b kh nn ............................................................................................ 302

Chng 4 B IU KHIN

4.1 Gii thiu .................................................................................................... 3134.2 B iu khin bng tip im ..................................................................... 3184.3 B iu khin dng Vi x l ....................................................................... 3204.4 B iu khin dng PLC - My tnh .......................................................... 3224.5 B iu khin dng bin tn ....................................................................... 326

TI LIU THAM KHO


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Chng 1: Cc khi nim chung

Trang 1

Chng 1

CC KHI NIM CHUNG

1.1 Khi nim v phn loi h thng iu khin t ng1.1.1 Khi nim v iu khin

a. iu khin t ngnh ngha: iu khin l qu trnh thu thp thng tin, x l thng tin v

tc ng ln h thng p ng ca h thng gn vi mc ch nh trc.

iu khin t ng l qu trnh iu khin khng c s tc ng ca con ngi.

o Cc v d: iu khin tc ng c iu khin nhit iu khin v tr bn my iu khin cc h thng ng dng trong sinh hot: ca t ng, bi u xe,

thang my.

iu khin cc qu trnh cng nghip ni chung.b. Ti sao cn phi iu khin t ng

p ng ca h thng khng tha mn yu cu. Tng chnh xc. Tng nng sut. Tng hiu qu kinh t.

1.1.2 Phn loi h thng iu khina. Phn loi da trn m t ton hc ca h thng:

H thng lin tc: H thng lin tc c m t bng phng trnh vi phn. H thng ri rc: H thng ri rc c m t bng phng trnh sai phn.


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Trang 2

H thng tuyn tnh: h thng c m t bng h phng trnh vi phn/ saiphn tuyn tnh.

H thng phi tuyn: H thng c m t bng h phng trnh vi phn/ saiphn phi tuyn.

H thng bt bin theo thi gian: H s ca phng trnh vi phn/ sai phnm t h thng khng i.

H thng bin i theo thi gian: H s ca phng trnh vi phn/ sai phnm t h thng thay i theo thi gian.

b. Phn loi da vo s ng vo ra ca h thng: H thng mt ng vo mt ng ra (h SISO): (Single Input Single

Output)

H thng nhiu ng vo nhiu ng ra (h MIMO): (Multi Input MultiOutput)

a s cc h thng trong thc t u l h phi tuyn bin i theo thi gian,

nhiu ng vo, nhiu ng ra.Cho d h thng iu khin thuc loi no i na th trn mt h thng

cng phi c cc thit b thc hin cho vic iu khin h thng . Trong

mn hc ny phn ra cc thit b theo cc thnh phn c bn ca mt h thng

kho st.

1.2 Cc thnh phn c bn ca mt h thng iu khin t ngH thng iu khin c ba thnh phn c bn: i tng, b iu khin v

cm bin

Hnh 1.1 H thng iu khin c bn.


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a. i tng iu khii tng i

t c cc y

qut chung, cn p

thng mang tnh b

o i tng i ng c DC:

c c tnh ng

ng c AC:dng vi loi

thng c

H

ng c bccho tng cc,

rt nhiu trong

Chng 1: C

Trang 3

n (plant, process):

khin chnh l mc tiu thit yu m c

cu mong mun. Trn y t i t

n bit r i tng v h thng.

o hm, c ngha c th bao gm nhiu

u khin thng l cc ng c:

loi ng c s dng ngun in DC,

u lc ln, d iu khin

Hnh 1.2 ng c DC.

loi ng c s dng ngun in AC lo

ng c khng ng b mt pha v

iu khin dng bin tn

h 1.3 ng c khng ng b mt v ba

: l loi ng c s dng ngun DC vi d

oi ng c ny lm vic c chnh x

iu khin t ng nht l trong cc m

c khi n m chung

ng ta cn tc ng

ng mang tnh khi

Thng thng h

i tng.

i loi ng c ny

i ny hin rt thng

a pha, hai loi ny

pha.

ng xung iu khin

cao c ng dng

cng c.


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H

o M hnh i i tng i Hi tip: l e

khin.

B iu khinkhin tc ,

phn hi tip

Chng 1: C

Trang 5

h 1.6 M hnh iu khin ng c AC ba

khin ng c bao gm:

khin l ng c DC.

coder ly tn hiu tc t trc ng

: l mt mch iu khin c tch hp

iu khin giao tip hin th trn my tn

hiu chnh sa sai.

Hnh 1.7 M hnh iu khin ng c D

c khi n m chung

pha.

c quay v b iu

t nhiu mch iu

h v giao tip thnh

.


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o M hnh i i tng i Cm bin: l c B iu khin

mc nc tron

o M hnh i

o M hnh i

Chng 1: C

Trang 6

khin bn nc:

khin: l mc nc trong bn.

m bin in dung kim tra mc nc tro

: l mch dng chip vi iu khin lp t

g bn theo yu cu.

nh 1.8 M hnh iu khin bn nc

khin my ng gi:

Hnh 1.9 M hnh iu khin my ng g

khin qu trnh phn loi v ng hp s

u(t)

Motor

c khi n m chung

ng bn

rnh iu khin cho

n.

i.

n phm:

qin

qout

h(t)


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Trang 7

Hnh 1.10 M hnh iu khin qu trnh phn loi v ng hp sn phm.

o M hnh iu khin qu trnh nung v vn chuyn sn phm:

Hnh 1.11 M hnh iu khin qu trnh nung v vn chuyn sn phm.

b. B iu khin ( Controller ):B iu khin (Controller): L thnh phn quan trng quyt nh kh nng

hot ng v chnh xc ca h thng. B phn ny thng thng c tch

hp di dng cc board mch iu khin, c th c cc loi sau:

IC iu khin trung tm (CPU) kt hp vi cc card iu khin phn theomodul (i vi h thng qui m ln).

Cc b iu khin kh trnh PLC (Programable Logic Controller), vi x l(h thng nhng)

My tnh thng qua cc card giao tip iu khin (PCI) S dng cc b iu khin PMAC (Programable Multi-Axies Controller)

trong cc my gia cng c kh CNC.


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Trang 8

S dng cc b iu khin thng qua bin tn. S dng iu khin qua h thng van kh nno Card iu khin DSP v PCI: H tr thng qua kt ni giao tip vi my

tnh v cc thit b hin th khc

Hnh 1.12 Card iu khin DSP v PCI

o Cc b logic kh trnh: S dng cc b lp trnh di dng hm c ccloi theo ng dng ln nh khc nhau nh:

B iu khin lp trnh PLC dng cho cc ng dng ln

Hnh 1.13 B lp trnh PLC.

B iu khin Logo! dng trong cc ng dng c va v nh

Hnh 1.14 B lp trnh Logo!.


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Trang 9

B iu khin ZEN dng trong cc ng dng c va v nh

Hnh 1.15 B lp trnh ZEN.

o H thng iu khin in kh nn c chc nng: L c cu bin i nng lng. L phn t a tn hiu v x l cc tn hiu ra. Cc c cu iu khin v iu chnh lm nhin v khc nhau. Ty thuc

vo nhin v ca h thng m cc c cu ny chia ra lm ba loi: c cu

chnh p, c cu chnh lu lng v c cu chnh hng.

Hnh 1.16 Ngun cp kh nn.

o Bin tn: Dng iu khin tc ng c khng ng b 1 pha v 3pha. S dng trong cc h thng truyn ng in.


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Trang 10

Hnh 1.17 Bin tn.

c. Cm bin:o Cm bin (Sensor):

L thit b chuyn cc i lng vt l thnh cc tn hiu in cung cp cho

h thng nhm nng cao kh nng linh hot v chnh xc trong iu khin.

Nh vy h thng iu khin t ng chnh l mt h thng iu khin kn vi

vng hi tip (Feedback ) c thc hin t tn hiu thu v t cm bin. Cc loi

cm bin thng gp nh:

Cm bin quang. Cm bin v tr v dch chuyn. Cm bin o gc. Cm bin vn tc.

Cm bin gia tc v rung. Cm bin lc v bin dng

Cc cm bin trn c th cho tn hiu tng t (Analog) hoc tn hiu s

(Digital), ngoi ra cn s dng cc b m ho v tr, m ho gc dch chuyn

(Encoder, Tachometter)


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Trang 11

Hnh 1.18 Cc loi cm bin thng dng.

Hnh 1.19 Cm bin quang.

Hnh 1.20 Cm bin tim cn.


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Trang 12

Hnh 1.21 Encoder.

o ng dng cm bin quang trong cng nghip:

Hnh 1.22 Cc ng dng cm bin quang trong cng nghip.

1.3 Cc v d v h thng iu khin t ng1.3.1 H thng iu khin ng c

o ng c (AC, DC) l thit b truyn ng c s dng rt ph bin trongcc nh my v dy chuyn sn xut.

oC ba bi ton iu khin ng c thng gp: iu khin tc , iukhin v tr v iu khin moment.

a. Ba kiu iu khin ng c:Ba ng dng iu khin ng c:

iu khin tc my git quay thun nghch v thay i tc . iu khin thang my di chuyn tnh tin ln xung.


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Trang 13

iu khin bng ti chy vng trn.

Hnh 1.23 ng dng iu khin ng c.

b. H thng iu khin ng c DC: i tng iu khin: ng c AC hoc DC B iu khin: iu khin in DC (DC Driver) hay iu khin in AC

(AC Driver) cn gi l bin tn (Inverter)

Hnh 1.24 H thng iu khin tc ng c DC.

1.3.2 H thng iu khin nhit o Nhit l i lng tham gia vo nhiu qu trnh cng ngh nh: sn

xut xi mng, gch men, nha, cao su, ha du, ch bin thc phm,


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Trang 14

o Mc tiu iu khin l gi cho nhit n nh (iu khin n nh ha)hay iu khin nhit thay i theo c tnh thi gian nh trc (iu

khin theo chng trnh).

Hnh 1.25 S h thng n nh nhit .

a. Cc nh my sn xut:

Hnh 1.26 Cc nh my sn xut xi mng v giy.

b. H thng iu khin l nhit:H thng iu khin l nhit bao gm:

i tng iu khin: nhit trong l nhit vi yu cu phi c gi chon n nh theo gi tr yu cu.


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Trang 15

B iu khin l mt thit b t ng c ch to lm vic theo chc nngv yu cu thc t nh chuyn nhit t l nhit v hin th ln mn hnh

hin th v gi tn hiu iu khin iu khin l nhit n nh nhit .

Cm bin: c dng l loi cm bin nhit.

Hnh 1.27 H thng iu khin l nhit.

1.3.3 H thng iu khin mc cht lng:a.

S mch iu khin:

B iu khin mc cht lng: (hnh v tham kho t gio trnh c s t

ng hc, Lng Vn Lng, NXB i hc quc gia)

Hnh 1.28 B iu khin mc cht lng.


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Trang 16

i tng iu khin: H thng iu khin mc cht lng thng gp trongcc qu trnh cng nghip nh ch bin thc phm, nc gii khc, cc h

thng x l nc thi

B iu khin: iu khin mc cht lng, iu khin lu lng cht lng. Cm bin c dng cc loi cm bin o mc cht lng:

Cm bin o dch chuyn: bin tr, encoder. Cm bin p sut. Cm bin in dung.

b. M hnh iu khin mc cht lng trong phng th nghim:

Hnh 1.29 M hnh b iu khin mc cht lng.

1.3.4 iu khin ng c ba pha dng bin tna. Vai tr ca ng c khng ng b 3 pha trong h thng sn xut:

Chuyn in nng thnh ng nng.

S dng trong cc h thng truyn ng in.


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Hnh

Nguyn l hoKhi cp ngun

chy vi tc gn

b. Chc nng ca b

o Dng i iu khin th n nh tc Khi ng m Hn dng kh Bo v qu ti Nng cao cht Gim h thn Tit kim nn

Chng 1: C

Trang 17

1.30 Nguyn l hot ng ca ng c b

t ng ca ng c khng ng b 3 pha

3 pha vo 3 cun dy Stator: Ni Y hay

bng 60*f/p.

in tn:

Hnh 1.31 Bin tn.

khin tc ng c KB 3 pha

y i tc ng c KB 3 pha

ng c KB 3 pha

m v dng mm ng c

ng

, kt ti

lng sn phm

c (hp s, rulo,)

g lng,

c khi n m chung

pha.

i th ng c s


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o Dng kh

o iu khin

1.3.5 ng dng trongo S cu th

S cu t

phn chnh:

bin. Ngoi

Hnh 1.34

Chng 1: C

Trang 18

i ng mm v dng mm ng c:

Hnh 1.32 Khi ng mm ng c.

n nh tc ng c khng ng b 3

Hnh 1.33 n nh tc ng c.

iu khin robot cng nghip

nh mt robot cng nghip chuyn dng:

nh mt robot cng nghip chuyn dn

b iu khin, i tng iu khin (c

a n cn c thm cc thnh phn h tr n

S cu thnh mt robot cng nghip c

c khi n m chung

pha:

g cng bao gm ba

nh tay robot), cm

h hnh 1.34

huyn dng.


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Trang 19

o Robot hn im (Ngun KUKA, Inc) v robot phu thut (Ngun Accury,Inc):

Hnh 1.35 Robot hn im. Hnh 1.36 Robot phu thut.

o Robot song song 6 bc t do:Theo s tin b ca khoa hc k thut, cc Robot ngy cng c ch to

nh gn hn, thc hin c nhiu chc nng hn, thng minh hn.

Robot song song 6 bc t do Merlet.(Ngun : Dr. J. - P. Merlet v Prof. V.

Hayward.)

Hnh 1.37 Robot song song 6 bc t do.

o Robot c s dng trong cng on cp liu v lp rp:


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Trang 20

Hnh 1.38 Robot c s dng trong cng on cp liu v lp rp

o Cc ng dng Robot trong cc lnh vc thm him, qun s, v tinh:

Hnh 1.39 Robot trong cc lnh vc thm him, qun s, v tinh.

o Robot chuyn ng bn chn (Ngun: AIBO, SONY, Nht Bn) vMobile Robot tc v (Ngun: SDR-4X, SONY, Nht Bn)

Hnh 1.40 Robot chuyn ng bn chn.


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Chng 2: Cm Bin & Chuyn i

Trang 21

Chng 2

CM BIN V CHUYN I

2.1 Gii thiuCm 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 th o v x l

c.

Trong qu trnh sn xut c nhiu i lng vt l nh nhit , p sut, tc ,

tc quay, nng pH, nhn... cn c x l cho o lng, cho mc ch iu

khin truyn ng. Cc b cm bin thc hin chc nng ny, chng thu nhn, p

ng cc kch thch.

Cm bin cng c xem nh mt k thut chuyn i cc i lng vt l

gm nhit , p sut, khong cch... sang mt i lng khc c th nh gi tt

hn. Cc i lng ny phn ln l tn hiu in.

Th d: in p, dng in, in tr hoc tn s dao ng. Cc tn khc ca b

cm bin: Sensor, b cm bin o lng, u d, van o lng, b nhn bit hoc bbin i.

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 nh (in

p, dng in, tr khng) cha thng tin cho php ta c th xc nh gi tr ca i

lng in , c trng (s) chnh l hm ca i lng cn o (m)

s = F(m) (2.1)

Ngi ta gi (s) l i lng u ra hay l phn ng ca cm bin, (m) l i

lng u vo hay gi l kch thch. Thng qua o c (s) cho php nhn bit gi tr

ca (m).

V d hnh nh cc cm bin thng dng c m t nh hnh 2.1


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Trang 22

Hnh 2.1 Cc loi cm bin thng dng hin nay

Cc b cm bin c s dng nhiu trong cc lnh vc kinh t v k thut. Cc

b cm bin c bit v rt nhy cm c s dng trong cc th nghim cc lnh vc

nghin cu khoa hc. Trong lnh vc t ng ho ngi ta s dng cc sensor thng

thng hay cc cm bin c chc nng c bit.

2.2 ng cong chun ca cm bin2.2.1Khi 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 s=F(m) hoc bng th.

Hnh 2.2 (a) ng cong chun b) ng cong chun ca cm bin tuyn tnh ha.

Da vo ng cong chun ca cm bin, ta c th xc nh gi tr micha bit

ca mthng qua gi tr o csicas. d s dng, ngi ta thng ch to cm


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Trang 23

bin c s ph thuc tuyn tnh gia i lng u ra v i lng u vo, phng

trnhs= F(m)c bin i di dng:

s = am +b (2.2)

vi a, bl cc h s, khi ng cong chun l ng thng.

2.2.2 Phng php chun cm binChun 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 c s xy dng ng cong chun di dng d nhn bit hn (

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 sica s v dng ng cong chun.

a. Chun n ginTrong 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 tr xc nh khng i

ca i lng o u vo. Vic chun tin hnh theo 2 cch:

o 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.

o Chun gin tip: kt hp cm bin cn chun vi mt cm bin so snh c snng cong chun, c hai c t trong cng iu kin lm vic.

b. Chun nhiu lnKhi cm bin c phn t b tr (tr c hoc tr t), gi tr o 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:

o 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.


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Trang 24

o o gi tr u ra theo mt lot gi tr tng dn n gi tr cc i ca i lngo u vo.

o 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.

2.3 Cc c trng c bn ca cm bin2.3.1 nhy ca cm bin

a. Khi nimi vi cm bin tuyn tnh, gia bin thin u ra s v bin thin u vo m

c s lin h tuyn tnh:

mSS = . (2.3)

m

SS

= : gi l nhy ca cm bin. (2.4)

Trng hp tng qut, biu thc xc nh nhy S ca cm bin xung quanh

gi tr mica i lng o xc nh bi t s gia bin thin s ca i lng u rav bin thin m tng ng ca i lng o u vo quanh gi tr :

immm

SS

=

= (2.5)

b. Lu php o t chnh xc cao, khi thit k v s dng cm bin cn lm cho

nhy S ca n khng i, ngha l t ph thuc nht vo cc yu t:

o Gi tr ca i lng cn o m v tn s thay i ca n.o Thi gian s dng.o 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.


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Trang 25

2.3.2 tuyn tnh ca cm bina. Khi nim

Mt cm bin c gi l tuyn tnh trong mt di o xc nh nu trong di ch

c nhy 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 nhtKhi 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 (si, mi) nhn c bng thc nghim thng khng nm trn cng

mt ng thng.

ng thng c xy dng trn c s cc 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:

bmaS += . (2.6)

vi( )

=

22

...

ii

iiii

mmN

msmsNa ;

( )

=

22

2 ...

ii

iiiii

mmN

msmmsb (2.7)

c. lch tuyn tnhi 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.

2.3.3 Sai s v chnh xc ca cm bina.

Sai s


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Trang 26

Cc b cm bin cng nh cc dng c o 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

tr o c v gi tr thc ca i lng cn o. Gi x l lch tuyt i gia gi tr

o v gi tr thc x (sai s tuyt i), sai s tng i ca b cm bin c tnh bng:

100x

x= [%] (2.8)

b. Sai s ca b cm bin mang tnh cht c tnhBi 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

hoc thay 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 h o, do iu

kin s dng khng tt gy ra

Sai s ngu nhin:L sai s xut hin c ln v chiu khng xc nh. Ta c

th d on c mt s nguyn nhn gy ra sai s ngu nhin nhng khng th d

on c ln v du ca n. Nhng nguyn nhn gy ra sai s ngu nhin c thl:

o Do s thay i c tnh ca thit b.o Do tn hiu nhiu ngu nhin.o Do cc i lng nh hng khng c tnh n khi chun cm bin.

2.3.4 nhanh v thi gian p ng ca cm bina. nhanh ca cm bin

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 p ng l

i lng c s dng xc nh gi tr s ca nhanh.


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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 %.

b. Thi gian p ng tng ng ca cm binThi gian p ng tng ng vi % xc nh khong thi gian cn thit phi

ch i sau khi c s bin thin ca i lng o ly gi tr ca u ra vi chnh

xc nh trc. Thi gian p ng c trng cho ch qu ca cm bin v l

hm ca cc thng s thi gian xc nh ch ny.

o Trong trng hp s thay i ca i lng o: Trong trng hp s thay ica i lng o c dng bc thang, cc thng s thi gian gm thi gian tr khitng (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 hnh 2.3.

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 tng cng ca n.

o Thi gian tr khi gim tdc: Thi gian tr khi gim tdcl thi gian cn thit ilng u ra gim t 90% n 10% bin thin tng cng ca n.

Hnh 2.3 Cc khong thi gian c trng cho ch qu .


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2.3.5 Gii hn s dng ca cm binTrong qu trnh s dng, cc cm bin lun chu tc ng ca ng lc c hc, 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.

o Vng lm vic nh danh: Vng lm vic nh danh tng ng vi nhng iukin 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 nh danh ca cm bin.o Vng khng gy nn h hng: Vng khng gy nn h hng l vng m khi 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 nh danh 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 tr v vng lm vic nh danh cc c trngca cm bin ly li gi tr ban u ca chng.

o Vng khng ph hy: Vng khng ph hy l vng m khi cc i lng o hoccc 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 tr v vng lm vic nh danh 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.

2.4 Nguyn l ch to ca cm binCc cm bin c ch to da trn c s cc hin tng vt l v c phn

lm hai loi:


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o Cm bin tch cc:L cc cm bin hot ng nh mt my pht, p ng (s) lin tch, in p hay dng.

o Cm bin th ng:L cc cm bin hot ng nh mt tr khng trong png (s) l in tr, t cm hoc in dung.

Cc cm bin tch cc c ch to da trn c s ng dng cc hiu ng

vt l bin i mt dng nng lng no (nhit, c hoc bc x) thnh nng

lng in. Sau y m t mt cch khi qut ng dng mt s hiu ng vt l

khi ch to cm bin

2.4.1 Hiu ng nhit inHiu ng nhit ng dng trong ch to cc cm bin nhit . Hai dy dn (M 1)

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 T1v T2khc nhau, khi trong mch xut hin

mt sut in ng e(T1, T2) m ln ca n ph thuc vo s chnh lch nhit

gia T1v T2.

Hnh 2.4 Hiu ng nhit in.

Hiu ng nhit in c ng dng o nhit T1khi bit trc nhit T2,

thng chn T2= 0oC.

2.4.2 Hiu ng ha nhitMt s tinh th gi l tinh th ha nhit (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 ha nhit.


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Hnh 2.5 Hiu ng ha nhit.

Hiu ng ha nhit c ng dng o thng lng ca bc x nh sng. o

in p V ta c th xc nh c thng lng nh sng .

2.4.3 Hiu ng p inMt s vt liu gi chung l vt liu p in (nh thch anh) khi b bin dng

di tc ng ca lc c hc, 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.

Hnh 2.6 Hiu ng p in.

2.4.4 Hiu ng cm ng in tKhi 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 ttrong 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.

Hnh 2.7 Hiu ng cm ng in t.


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Hiu ng cm ng in t c ng dng xc nh tc dch chuyn ca vt

thng qua vic o sut in ng cm ng.

2.4.5 Hiu ng quang inHiu 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 x in t ni chung) c bc sng nh hn mt ngng

nht nh.

Hiu ng quang pht x in t: (hay cn gi l hiu ng quang in ngoi) l

hin tng cc in t c gii phng v thot khi b mt vt liu to thnh dng c

th thu li nh tc dng ca in trng.

2.4.6 Hiu ng quang-in tKhi 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.

Hnh 2.8 Hiu ng quang- in t.

2.4.7 Hiu ng HallHiu ng Hall c ng dng xc nh v tr ca mt vt chuyn ng. Vt

cn xc nh v tr lin kt c hc 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.


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Hnh 2.9 Hiu ng Hall.

o Nguyn l ch to cm bin th ng: Cm bin th ng thng c ch to tmt tr khng c cc thng s ch yu nhy vi i lng cn o. Gi tr ca tr

khng ph thuc kch thc hnh hc, tnh cht in ca vt liu ch to (nh

in tr sut , t thm , hng s in mi ). V vy tc ng ca i lng

o c th nh hng ring bit n kch thc hnh hc, tnh cht in hoc ng

thi c hai.o S thay i thng s hnh hc: S thay i thng s hnh hc ca tr khng 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 t ng s

ng vi mt gi tr xc nh ca tr khng, cho nn o tr khng c th xc nh

c v tr ca i tng.

oPhn t bin dng ca cm bin:Trong cm bin c phn t bin dng, s bindng 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 tr khng ca cm bin. S thay i tr

khng do bin dng lin quan n lc tc ng, do lin quan n i lng

cn o. Xc nh tr khng ta c th xc nh c i lng cn o. Cc i

lng cn o c kh nng lm thay i tnh cht in ca vt liu s dng ch to

cm bin:


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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 tp

Hp kim st t

V tr (nam chm) Vt liu t in tr: Bi,InSb

Hnh 2.10 S chuyn i gia cc i lng ca cm bin

2.5 Phn loi cm binCm bin c phn loi theo nhiu tiu ch khc nhau. Ty theo cch chn

m ngi ta c th phn loi cm bin theo cc cch sau:

a. Theo nguyn l chuyn i gia p ng v kch thch.


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Hin tng Chuyn i gia p ng v kch thch

Vt l

Nhit in.

Quang in

Quang t.in t

T in

Ha hc

Bin i ha hc

Bin i in ha

Phn tch ph

Sinh hcBin i sinh haBin i vt l

Hiu ng trn c th sng

b. Theo dng kch thch.Kch thch Cc c tnh ca kch thch

m thanh

Bin pha, phn cc

PhTc truyn sng

in

in tch, dng in

in th, in p

in trng

in dn, hng s in mi

T

T trng

T thng, cng t trng.

t thm

C

V tr

Lc, p sut

Gia tc, vn tc, ng sut, cng

M men

Khi lng, t trng


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Trang 35

nht

Quang

Ph

Tc truyn

H s pht x, khc x

Nhit

Nhit

Thng lng

T nhit

Bc xKiu: Nng lng

Kiu: Cng

c. Theo tnh nng. nhy chnh xc phn gii tuyn tnh

Cng sut tiu thd. Theo phm vi s dng

Cm bin cng nghip Cm bin nghin cu khoa hc Cm bin mi trng, kh tng Cm bin thng tin, vin thng Cm bin nng nghip Cm bin dn dng Cm bin giao thng vn ti

e. Theo thng s ca m hnh mch in thay tho Cm bin tch cc (c ngun): u ra l ngun p hoc ngun dng.


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o Cm bin thcn c thm ng

tch cc th kh

R, L, Ctuyn

f. Cc loi cm bin tho Cm bin timo Cm bin quano Cm bin muo Cm bin thngo Cm bin si qo Cm bin lc co Cm bin nhit.o Cm bin v tro Cm bin lu lo Cm bin siu

g. K hiu cc loi c

Hnh 2

Chng 2: Cm

Trang 36

ng (khng c ngun): Cm bin gi l

un nng lng ph hon tt nhim

g cn. Cm bin th ng c c trn

tnh hoc phi tuyn.

ng s dng trong cng nghip v dn

n.

.

c.

minh.

ang.

ng p sut.

dch chuyn.

ng.

m.

bin

.11 K hiu cc loi cm bin thng d

Bin & Chuyn i

th ng khi chng

o kim, cn loi

g bng cc thng s:

dng

g


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Cm bin c k hiu nh hnh 2.11, ty theo loi cm bin m trong k hiu s

km thm cc k hiu ca cun dy cho cm bin in cm, t cho cm bin in

dung V d: Hnh 2.12 l k hiu ca cm bin in dung, ng ra dng ON/OFF loi

thng h, chuyn mch dng.

Hnh 2.12 K hiu cm bin in dung

2.6 Mch o cm bin2.6.1S mch o

Mch o bao gm ton b thit b o (trong c cm bin) cho php xc nh

chnh xc gi tr ca i lng cn o trong nhng iu kin tt nht.

o u vo ca mch, cm bin chu tc ng ca i lng cn o gy nntn hiu in mang theo thng tin v i lng cn o.

o u ra ca mch, tn hiu in qua x l c chuyn i sang dng cth c c trc tip gi tr cn tm ca i lng o. Vic chun h o m

bo cho mi gi tr ca ch th u ra tng ng vi mt gi tr ca i lng

o tc ng u vo ca mch.

Hnh 2.13 S mch o nhit bng cp nhit


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o Trn thc t, do cc yu cu khc nhau khi o, mch o thng gm nhiuthnh 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 kh in

dung k sinh, cc b chuyn i nhiu knh, b khuch i, b so pha lcnhiu, b chuyn i tng t - s, b vi x l, cc thit b h tr...

o Hnh 2.14 biu din s khi mt mch in o in th trn b mt mngnhy quang c lp rp t nhiu phn t.

Hnh 2.14 Mch o in th b mt

2.6.2Mt s phn t c bn ca mch oa.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 nhiu trasistor v cc in tr, t

in ghp ni vi nhau. u vo ca mch, cm bin chu tc ng ca i

lng cn o gy nn tn hiu in mang theo thng tin v i lng cn o.

Hnh 2.15 S mch khuch i thut ton

1) My pht chc nng

2) Cm bin in tch

3) Tin khuch i

4) So pha lc nhiu

5) Khuch i

6) Chuyn i tng t s

7) My tnh


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b.B khuch i o lng IAB khuch i o lng IAc hai u vo v mt u ra. Tn hiu u ra t

l vi hiu ca hai in p u vo:

UAUUAUra == + )( (2.9)

Hnh 2.16 S mch khuch i o lng gm 3 b KTT ghp in tr

c.Kh in p lcho i vi mt b khuch i thut ton l tng khi h mch phi c in p

ra bng khng khi hai u vo ni mass.

o Thc t v cc in p bn trong nn to ra mt in p nh (in p phncc) u vo khuch i thut ton c vi mV, nhng khi s dng mch

kn in p ny c khuch i v to nn in p kh ln u ra. kh

in p lch c th s dng s hnh nh sau, bng cch iu chnh bin

tr R3.


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Hnh 2.17 S mch kh in p lch

d.Mch cuo Cu Wheatstone thng c s dng trong cc mch o nhit , lc, p

sut, t trng... Cu gm bn in tr R1, R2, R3 c nh v R4 thay i

(mc nh hnh 2.18) hot ng nh cu khng cn bng da trn vic pht

hin in p qua ng cho ca cu.

o u ra ca mch, tn hiu in qua x l c chuyn i sang dng cth c c trc tip gi tr cn tm ca i lng o. Vic chun h o m

bo cho mi gi tr ca ch th u ra tng ng vi mt gi tr ca i lng

o tc ng u vo ca mch.

Hnh 2.18 S mch cuWheatstone


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Hnh 2.

Cm bin tim cn

mt vt th vi cm bi

cn c mt v tr rt qu

robot bt gi ly; pht h

cm bin thng dng l

Cm bin tim cn

o Loi cm ng t: c

v ch pht hin

o Loi cm ng in

in mi ln hn 1,

o Loi cm bin qua

tm o tng i x

o Loi cm bin siu

2.7.1 Cm bin tim c

2.7.1.1 Gii thiu cm

a. Hnh dng cm biCm bin cm ng

dng hnh ch nht nh h

Chng 2: Cm

Trang 42

19 Cm bin tim cn loi pht hin vt

l mt k thut nhn bit s c mt h

n in t khng cng tc (khng ng c

n trng trong thc t. Th d pht hin v

in chai, lon nhm trn bng chuyn.

gic (c hoc khng).

cc loi:

hai loi in cm v t cm, loi ny c

c nhng vt c t tnh

dung: tm pht hin ngn, pht hin

thng c b phn chnh nhy.

g c ba loi: xuyn sut, phn x v kh

c th ln n 30m, pht hin c hu

m: c th pht hin tt c cc vt tm ph

n cm ng t (Magnectic sensor)

bin tim cn cm ng t

n cm ng t

c rt nhiu hnh dng khc nhau, nh

nh 2.20

Hnh 2.20 Hnh dng cm bin t

Bin & Chuyn i

i v vt cn.

y khng c mt ca

m). Cm bin tim

t trn dy chuyn

n hiu ng ra ca

tm pht hin ngn

c cc vt c hng s

ch tn loi ny c

t cc vt.

t hin trung bnh

g thng s dng l


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b. Nguyn tc ch to cm ng tNguyn tc ch to cm bin t da theo hin tng cm ng t Hall

Hnh 2.21 Hin tng cm ng t Hall.Khi t mt tm vt liu mng (thng l bn dn) cho dng in I chy qua s

sinh ra mt t trng B c phng to vi dng in mt gc th s xut hin mt

in th Vhtheo hng vung gc gia B v I nh hnh 2.22

sin... BIKV hh = (2.10)

Trong Khl h s vt liu

Hnh 2.22 Hot ng cm ng t Hall.

Hiu ng Hall c dng ch to cm bin xc nh s di chuyn ca vt, vt

c gn vo thanh nam chm to t trng B. T trng do cun dy ca cm bin

to ra s thay i khi tng tc vi vt th kim loi do ch pht hin c vi vt

th l kim loi.


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2.7.1.2 Cm bin t lo

a. Hnh dngCm bin in c

dng l dng hnh tr tr

Cm ng t loi i

quanh n nhn bit vbin tim cn in cm c

ng dng khc nhau. C

tng l kim loi (nhn

phi l kim loi).

b. Cu to

Chng 2: Cm

Trang 44

Hnh 2.23 Nguyn tc chung ca cm bi

i in cm(Inductive sensor)

cng c rt nhiu hnh dng khc nha

v bc bng kim loi nh hnh 2.24

nh 2.24 Cc loi cm bin t loi in

n cm da vo in cm ca cun dy si

t. Cm bin loi in cm rt a dng n nhiu kch thc v hnh dng khc nh

m bin tim cn in cm c dng

chng khng th pht hin cc i t

Bin & Chuyn i

n t.

u, nhng thng s

cm.

h ra t trng xung

hnh 2.24. Cmu tng ng vi cc

pht hin cc i

g c cu to khng


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Phn cm ng

vo cun dy to c

thng a ra 2 d

s c led ch th bo

Hnh 2

Cu trc ca cm bi

o 1 - Cun dy v li

t trn cun dy l

bin, nn vng ny

o 2 - Mch dao ng

tn s cao khi c s

hiu ny s gim.

Chng 2: Cm

Trang 45

Hnh 2.25 Cu to cm bin t loi in

t bao gm cc thnh phn: Vng t tr

m ng t vi tn s lm vic t 300

cp kt ni ngun v mt dy tn hiu

hiu cm bin nhn thy vt trong vng

.26 Cu trc ca cm bin t loi in c

n gm 4 phn chnh nh hnh 2.26

erit: Phn ny to ra vng t trng nh

li ferit, vng t trng tp trung ph

tc ng ln vt cn o

: Chc nng mch ny to ra dao ng

tng tc ln b mt cm bin th bin

Bin & Chuyn i

m.

ng c to ra nh

n 800kHz, loi ny

a. Khi c tn hiu ra

c ng.

m.

hin tng cm ng

trc u ca cm

i dng tn hiu sin

dao ng ca tn


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o 3 - Mch pht hin: Chc nng mch ny da vo in th tham chiu pht

hin gi tr bin ca mch dao ng khi c vt tc ng ln b mt cm bin,

lc bin ny gim n mt gi tr cho php no s xut ra tn hiu ng ra

o 4 -Mch u ra: Ng ra l kt qu ca mch so snh ngng nhn bit c vt

nm trong tm hot ng ca cm bin hay khng, do tn hin ra dng

ON/OFF

c. Nguyn l hot ngCm bin cm ng t hot ng da trn nguyn tc thay i tng tc t trn b

mt ca cm bin nh hnh 2.27

Hnh 2.27 Cc thnh phn ca cm bin t loi in cm.

Tn s mch dao ng LC thng t 300Khz n 800 Khz c tnh theo cng

thc:

LCF

2

10 = (2.11)

nh hng ca dng in xoy lm thay i bin b dao ng LC. Mch pht

hin ngng (trigger) gim st s thay i bin v kch mch ng ra (output switch)

mi khi c s thay i vt ngng. Ng ra cm bin l tn hiu ON/OFF.


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Trang 47

Hnh 2.28 Trng thi tc ng ca cm bin t loi in cm.

Khi c vt th bng kim loi i vo vng t trng. T trng ny cm ng ln

vt th mt dng in xoay trn gi l dng in xoy. Dng in xoy to ra mt t

trng ngc chiu vi t trng ban u. T trng ny lm gim bin mch dao

ng LC bn trong cm bin. Hnh 2.28

Hnh 2.29 Hin tng t trng xoy ca cm bin t loi in cm.

T trng to ra xung quanh cun dy khi c dng in xoay chiu chy qua.

Khi c vt th bng kim loi a vo t trng. Dng in xoy s c cm ng vo

kim loi. Dng in xoy trong kim loi to ra t trng th hai ngc vi t trng


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ban u nh hnh 2.29. Dng in s b ngt qung khi c vt nt trn vt liu dn

in.

Cm bin tim cn in cm c thit k to ra mt vng in t trng, khi

mt vt bng kim loi tin vo khu vc ny, xut hin dng in xoy (dng in cm

ng) trong vt th kim loi ny. Hnh 2.30

Hnh 2.30 Nguyn l lm vic ca cm bin in cm.

Dng in xoy gy nn s tiu hao nng lng (do in tr ca kim loi), lm

nh hng n bin sng dao ng. n mt tr s no tn hiu ny c ghi

nhn. Mch pht hin s pht hin s thay i tn hiu v tc ng mch ra ln mc

ON hnh 2.31. Khi i tng ri khi khu vc in trng, s dao ng c lp li,cm bin tr li trng thi bnh thng.

Hnh 2.31 Hot ng ca cm bin tim cn in cm.


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Trang 49

Khi vt cn tc ng ln b mt ca cm bin, bin tn hiu ca mch dao

ng s thay i, bin ny s gim dn khi vt cng tin gn b mt tc ng. Khi

khong cch ln ng ra ca cm bin s cho ra mt xung v n ch bo s sng

ln.

d. Phn loiCm bin tim cn in cm c th phn lm 2 loi: Shielded (c bo v) v

unshielded (khng c bo v) nh hnh 2.32. Loi khng c bo v thng c tm pht

hin ln hn loi c bo v.

Hnh 2.32 Phn loi cm bin in cm.

o Cm bin tim cn in cm loi c bo v:c 1 vng kim loi bao quanh (hnh

2.33) gip hn ch vng in t trng vng bn, tuy nhin khi c lp bo v

ny th vng t trng cng b gii hn bt i lm cho cm bin c tm pht hinngn li. V tr lp t cm bin c th t ngang bng vi b mt lm vic .

o Cm bin tim cn in cm loi khng c bo v: khng c vng kim loi bao

quanh, khng th lp t cm bin ngang bng b mt lm vic (bng b mt kim

loi). Loi cm bin khng c bo v xung quanh phi c 1 vng khng c cha

kim loi phn u cm bin (hnh 2.34) v th tm pht hin c xa hn

nhng d b nh hng bi cc vt xung quanh lm bng kim loi.

Hnh 2.33 Cm bin tim cn in cm loi c bo v.


52/335


Trang 50

Hnh 2.34 Cm bin tim cn in cm loi khng c bo v.

c 2 loi cm bin c bo v v khng c bo v, nu c 1 b mt kim loi v

tr i din cm bin, khng nh hng n hot ng ca cm bin th b mt kim

loi ny phi cch b mt cm bin 1 khong cch c ln t nht gp 3 ln tm pht

hin ca cm bin.

e. u nhc imo u im

Khng chu nh hng ca m. Khng c b phn chuyn ng.

Khng chu nh hng ca bi bm.

Khng ph thuc vo mu sc.

t ph thuc vo b mt i tng hn so vi cc k thut khc.

Khng c vng cht (blind zone): cm bin khng pht hin ra i tng

mc d i tng gn cm bin.o Nhc im

Ch pht hin c i tng l kim loi.

C th chu nh hng bi cc vng in t mnh.

Phm vi hot ng ngn hn so vi cc k thut khc.

2.7.1.3 Cm bin t loi t cm:(Inductive Magnectic sensor)

a. Loi tc ng bng tip im:(Reed Switch: li g)


53/335

Cu to

Cm bin t loi t

o B phn cha tip

kh tr.

o Tip im (li g):

o Led ch bo v dy

Nguyn l hot n

Cm bin lo

khong cch cho p

li g lm ng ti

cn bng kim loi,

Khi t trng

ng li nh hnh 2.

Chng 2: Cm

Trang 51

ng bng tip im (li g) cu to g

im: L mt ng thy tinh bn trong c

lm bng cht c kh nng t tnh nh s

i ngun, tn hiu ra.

Hnh 2.35 Cu to cm bin t loi li

ny pht hin c tt c cc loi vt

p. T trng c to ra t cun dy c

p im. Cm bin b nh hng bi 3

hong cch vt cn.

to ra gn v tr ca li g, vi lc t

36

Hnh 2.36 Hai trng thi ca li g.

Bin & Chuyn i

m cc b phn sau:

a chn khng hay

t hay niken.

g.

liu dn in trong

m ng tc ng ln

u t: Nhit , vt

ln s ht li g


54/335

Khi c t tr

v ht nhau, hai ti

ng bng tip i

S ph thuc cc t

o V tr ca im tc

o Dng cc i cn

b. Loi tc ng bng Cu to

Cm bin t loi t

o Mch t: l mt m

cm ng vo.

o Cun dy mch t:

o Led ch bo v dy

HnhCm bin t l

u thu khi c v

tc ng bng li

bng mch t.

Nguyn l hot n

Chng 2: Cm

Trang 52

g i qua vng cng tc th s lm cho h

im s c ni li. y l c s

.

trng khc nhau cn c trnh:

ng ph thuc vo khong cch dch chu

c gii hn trnh chy tip im.

t cm(Inductive Magnectic sensor)

ng bng mch t cu to gm cc b

ch t tn s cao c tc ng khi c

mt b dy qun trn mch t.

i ngun, tn hiu ra.

2.37 Cu to cm bin t tc ng bngi tc ng bng mch t da vo s t

t ti gn. Cm bin c cu to gm cc

ch khc tip im trong cm bin t l

Bin & Chuyn i

i tip im nhim t

h to cm bin tc

yn.

hn sau:

t trng bn ngoi

trng.ng ca t trng

phn ging nh loi

i li g c thay


55/335

Cu to gm

ng thu cm bin,

trng u thu v l

snh pht hin cho

Hnh 2.38 C

Cn ch khi thc

o Thit b lm vic tr

o Trnh dng loi c

2.7.1.4 c tnh v c

a.c tnh

Cm bin ti

thng c hai loi n

o Cm bin tim cn

t b nhiu bi kim l

o Cm bin tim cn

mt cm bin nn k

xung quanh.

Chng 2: Cm

Trang 53

t b to dao ng tn s cao, dao

khi vt c t trng tin n gn th s l

m cho mch dao ng ca cm bin b

g ra cm bin dng on/off.

thnh phn chnh ca cm bin t tc

in trn cc dng t khc nhau.

ng thi ngm tn s lm vic cao - 1kHz

bin ny nhng ni c nhiu nh h

thng s s dng

cn ty theo cu to s c cc c tnh

h sau

oi c bo v:t trng c tp trung t

oi xung quanh, tuy nhin khong cch

Hnh 2.39 Cm bin t loi c bo v

oi khng c bo v:khng c bo v t

hong cch o s di hn, tuy nhin d

Bin & Chuyn i

g ny to t trng

m nh hng n t

nh hng, mch so

ng bng t trng.

g ca t trng.

s dng khc nhau,

rc mt sensor nn

s ngn i.

.

trng xung quanh

nhiu bi kim loi


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b. Cc thut ng th Vt chun (Standar

Mt vt c

hp pht huy

Khong cch tc

Khong cch

tnh ton nh l sai

cp. Trong mt vi

khong cch tc

n khi n n gnxem xt khi c l

2.42

Khong cch ho

Khong cch

vi nhit dao

sai s trong qu tr

Chng 2: Cm

Trang 54

Hnh 2.40 Cm bin t loi khng c b

ng s dng

Object)

xem l chun nu: hnh dng, vt liu, k

c cc c tnh k thut ca cm bin.

Hnh 2.41 M t vt chun.

g (Rated Distance): Sn

c ng l mt gi tr l thuyt m n k

s ca qu trnh sn xut, nhit hot

trng hp cm bin c th pht hin r

g ny. Hoc c trng hp vt th khn

hn khong cch tc ng. C mt ving khong cch tc ng trong mi tr

t ng hiu qu (Effective Operating Dis

ot ng hiu qu iu kin ngun i

ng trong khong t 23oC 0.5oC. N d

h sn xut. Khong cch hot ng hi

Vt chhnh dthc, t

Bin & Chuyn i

o v.

ch c ca vt ph

hng ph thuc vo

ng v in p cung

a vt th nm ngoi

c pht hin cho

gii hn phi cng hp c th. Hnh

ance): Sr

n cung cp n nh

a vo vic tnh ton

qu khong 10%

n: vt liu,g, kch

c


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Trang 55

ca khong cch tc ng. iu ny c ngha l vt th s c pht hin trong

khong t 0 n 90% ca khong cch tc ng. Ty thuc vo mi thit b tuy

nhin khong cch tc ng hiu qu c th xa hn 110% ca khong cch tc

ng. Hnh 2.42

Khong cch chuyn mch hu ch (Useful Switching Distance): Su

Khong cch chuyn mch hu ch l khong cch chuyn mch c tnh

ton theo iu kin in p v nhit l thuyt. Khong cch chuyn mch hu

ch th bng khong 10% ca khong cch hot ng hiu qu. Hnh 2.42

Khong cch hot ng chc chn (Guaranteed Operating Distance): Sa

Khong cch hot ng chc chn l khong cch chuyn mch cho s hot

ng ca cm bin tim cn trong phm vi iu kin hot ng c th c th chp

nhn c m bo. Khong cch hot ng chc chn nm trong khong

081% ca khong cch hot ng. Hnh 2.42

Hnh 2.42 Khong cch hot ng ca cm bin.

Cc chuyn mch ca cm bin tim cn ch p ng li vi vt th khi vt

th nm trong khu vc xc nh ng trc b mt ca cm bin. im m

cm bin tim cn nhn ra c mt vt th mang n gi l im tc ng. V

im m khi vt th i ra lm thit b chuyn li trng thi ban u gi l im

thot. Khong cch gia 2 im ny gi l vng tr (hysteretis zone). Hnh 2.43


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Trang 56

Hnh 2.43 Cc im chuyn mch ca cm bin.

Khong cch pht hin (Detecting Distance)

Khong cch pht hin l khong cch t b mt cm bin u cm bin

ti v tr vt chun xa nht m cm bin c th pht hin. Hnh 2.44

Hnh 2.44 M t khong cch pht hin.

Khong cch ci t (Sitting Distance)

Khong cch ci t l khong cch t b mt cm bin u cm bin ti

v tr vt cm bin cm bin c th pht hin vt n nh (thng khong cch

ny bng 70% n 80% khong cch pht hin). Hnh 2.45

Khong cch pht hin

Vtcm

bin

Khong cch Reset

Cm bintim cnB mt

cm bin

ONOFF


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Trang 57

Hnh 2.45 M t khong cch ci t.

Thi gian p ng (Response Time)

o T1 l khong thi gian t lc i tng chun chuyn ng i vo vng

pht hin ca cm bin ti khi u ra cm bin bt v ON.

o T2 l khong thi gian t lc i tng chun chuyn ng i ra khi vng

pht hin ca cm bin ti khi u ra cm bin tt v OFF. Hnh 2.46

Hnh 2.46 M t thi gian p ng.

Tn s p ng (Response Frequency)S ln tc ng lp li khi vt cm bin i vo vng hot ng ca cm

bin. Hnh 2.47

Vtcm

bin

Dy hot ng Cm bintim cn

B mtcm bin

Trong dy hot ng

goi dy hot ng

ON

OFF

T1 T2

Khong cch ci t

Vtcm

bin

Khong cch pht hin c lng

Cm bintim cn

B mtcm bin


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Trang 58

Hnh 2.47 M t tn s p ng.

c. Khong cch o v cc yu t nh hng Vt liu i tng (Material):

Vt liu i tng l khong cch pht hin ca cm bin ph thuc rt

nhiu vo vt liu ca vt cm bin. Hnh 2.48

Hnh 2.48 M t c tnh t ca vt liu.Cc vt liu c t tnh hoc kim loi c cha st s c khong cch pht

hin xa hn cc vt liu khng c cha t tnh hoc cha st. Hnh 2.48

Kim loi cu to nn vt th cng nh hng n khong cch vng tc

ng. Nhng khi mt kim loi no khc thp th mt h s chnh sa c s

dng hiu chnh.

Khong cchpht hinu sensor u sensor

Vt Vt

Kim loi khng c t tnh Kim loi c t tnh

Cm bintim cn

khong cch cm bin

M

M2M

T1 T2 T3

Vt cm bin

f=1/(T2+T2)


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Trang 59

Hnh 2.49 Biu m t dn theo c tnh t.

Kch c ca i tng (Size):

Nu vt cm bin nh hn vt th chun (test object) khong cch pht hin

ca cm bin s gim. Hnh 2.50

Hnh 2.50 M t kch thc tng i ca ca i tng.

B dy ca i tng (Size):

dy ca vt th l mt h s cn c xem xt. Khong cch vng tc

ng th khng i i vi vt chun. Tuy nhin i vi vt th khng c sttrong thnh phn nh ng thau (brass), nhm (aluminum) v ng (copper)

th s xy ra hin tng hiu ng b mt (skin effect). Khong cch vng cm

ng s gim khi dy ca vt th tng ln. Nu dy ca vt th khc so vi

vt chun th mt h s chnh sa s c dng iu chnh li.

Vi vt cm bin thuc nhm kim loi c t tnh (st, Niken, SUS), b

dy vt phi ln hn 1mm.

Khong cchpht hinu sensor

u sensor

Vt Vt

Kch thc vt ln Kch thc vt nh

dn ca vt

Khong cch cm bin

Iron

SUS

BrassAluminum

Copper


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Vi vt cm

cng mng th kho

Lp m bn ngo

Nu vt b m

Khng m

Zn (5 15m

Cd (5 15m

Ag (5 15m

Cu (10 20

Cu (5 15m

Cu (5 10m

Cu (5 10m

S giao thoa v

Cn phi ch

bin t k nhau ha

gia chng, dn

Chng 2: Cm

Trang 60

in thuc nhm kim loi khng c t

g cch pht hin cng xa. Hnh 2.51

Hnh 2.51 M t b dy ca i tng.

i ca vt (Plating):

th khong cch cm bin ca vt s b

dy v vt liu m Thp

100

) 90 1

) 100 1

) 60 9

) 70 9

) ---

) + Ni(Cu 1020m) 75 9

) + Ni(10m) Cr(0,3m) 75 9

nh hng bi kim loi xung quanh:

khi s dng nhiu cm bin, khi c ha

y i din nhau c th xy ra nhiu hoc

sai tn hiu u ra.

Bin & Chuyn i

nh, b dy ca vt

h hng

ng

100

0 95 105

10 95 105

85 100

95 105

95 105

---

95 105

hay nhiu hn cm

nh hng ln nhau


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Trang 61

Khi c nhiu cm bin tim cn c t st nhau, s lm vic sai ca cc

cm bin c th l nguyn nhn giao thoa. V th phi quy nh mt khong cch

nh nht gia 2 cm bin nh hnh 2.52

Hnh 2.52 Khong cch m t cho s giao thoa.

Khi cc cm bin c t trn bng kim loi, n i hi phi che chn cm

bin trnh nh hng bi cc vt bng kim loi ngoi tr vt cn pht hin.

V th phi quy nh mt khong cch nh nht gia cc cm bin nh hnh 2.53

Hnh 2.53 Khong cch m t nh hng bi kim loi

2.7.1.5 Cc loi u ra v cch mc ti

a. Loi u ra DC-2 dyKhi cm bin c 2 dy ra ngun cung cp DC loi ny thng ti c mc

vo l relay thc hin nh hnh 2.54 v hnh 2.55

o S tc ng ng ra

Hnh 2.54 S ng ra iu khin loi DC-2 dy.


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Trang 62

o S u dy

Hnh 2.55 S u dy ra ti loi DC-2 dy.

Ti c th mc dy ngun hoc dy mass cng ng

b. Loi DC-3 dyKhi cm bin c 3 dy ra ngun cung cp DC loi ny thng ti c mc

vo l relay thc hin nh hnh 2.56, hnh 2.57, hnh 2.58, hnh 2.59

o S tc ng ng ra

Hnh 2.56 S ng ra iu khin loi NPN.

Hnh 2.57 S ng ra iu khin loi PNP.


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Trang 63

o S u ni:

Hnh 2.58 S u dy ra ti loi 3 u dy ra.

Hnh 2.59 S u dy ra ti loi 3 u dy ra.

c. Loi AC-2 dyKhi cm bin c 2 dy ra ngun cung cp AC loi ny thng ti c mc

vo l relay thc hin nh hnh 2.60 v hnh 2.61

o S ng ra iu khin:

Hnh 2.60 S ng ra iu khin loi AC-2 dy.


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o S u dy:

d. Kt ni cm bin vCm bin c t

dng dy ra ca c

hnh 2.65

o Loi 2 u dy

Hnh 2.

Hnh 2.

Chng 2: Cm

Trang 64

Hnh 2.61 S u dy cho ti loi D

i PLC

h kt ni trc tip hay gin tip vo ng

bin hai hay ba dy nh cc hnh 2.62,

a:

62 S kt ni cm bin vi PLC loi A

63 S kt ni cm bin vi PLC loi

Bin & Chuyn i

-2 dy.

vo PLC, ty theo

nh 2.63, hnh 2.64,

C 220V.

C 24V.


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o Loi 3 u dy

Hnh 2.64

Hnh 2.65

e. Mt vi ch khi so Khi s dng c

nu khng cc

trong 2 dy nh

H

Trng hp d

o Loi AC-2 dy:

mong mun bi

d l nh hn

song vi ti nh

Chng 2: Cm

Trang 65

a:

kt ni cm bin vi PLC loi NP

kt ni cm bin vi PLC loi PNP

dng

m bin tim cn loi DC hay AC-2 dy,

inh lin bn trong s h hng. Ti c th

hnh 2.66

h 2.66 Kt ni ti vi cm bin loi 2 d

ng ti nh:

C th l nguyn nhn lm ti hot n

in p d. Nu dng ti di 5mA, ta p

in p p li ca ti bng cch kt ni

hnh 2.67

Bin & Chuyn i

DC -3 dy.

DC -3 dy.

phi kt ni vi ti

c kt ni vi 1

ra.

g p li khng nh

hi m bo in p

t in tr s song


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Trang 66

( )=I

VR S ; ( )W

R

VP S

2

= (2.12)

I: dng lm vic ca ti

R: in tr s

P: cng sut gii hn

Hnh 2.67 Kt ni ti vi cm bin loi AC- 2 dy ra ti nh.

o Loi DC-2 dy: Phi to dng trn cm bin tim cn nh hn dng p li

ca ti bng cch kt ni thm mt in tr s song song vi ti nh hnh

2.68

( )= offoS

II

V

R ; ( )WR

V

P

S2

= (2.13)

VS: ngun cung cp

Io: dng lm vic Min ca cm bin tim cn

Ioff: dng p li ca ti

R: in tr s

P: Tng s W ca in tr s

Hnh 2.68 Kt ni ti vi cm bin loi DC-2 dy ra ti nh.


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Trang 68

Hnh 2.74 Cm bin pht hin m hay kim loi ri.

2.7.2 Cm bin in dung (Capacitive Sensor)

2.7.2.1 Gii thiu cm bin in dunga. Hnh dng

Cm bin in dung thng c cu to dng tr trn bn ngoi c bao

bc bi lp nha do nh hnh 2.75

Hnh 2.75 Cm bin tim cn loi in dung.

Cm bin in dung dng pht hin cc loi vt th c hng s in mi ln

hn hng s in mi khng kh nh: Nha, thy tinh, g, kim loi,... Cm bin

tim cn in dung ging v kch thc, hnh dng, c s hot ng so vi cm

bin tim cn in cm. im khc bit cn bn gia chng l cm bin tim cn


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in dung to ra v

in t trng. C

liu kim loi cng n

b. Cu to

Hn

Cm bin i

ngun, in cc ni

Cng ging n

dung c 4 phn nh

in cc, tip theo

mch ng ra cng c

Chng 2: Cm

Trang 69

ng in trng cn cm bin tim cn

bin tim cn in dung c th pht hi

h khng phi kim loi. Hnh 2.76

Hnh 2.76 Cm bin in dung pht hi

h 2.77 Cu to cm bin tim cn loi i

dung c cu to bao gm cc thnh

mass, led ch bo v nt hiu chnh n

cm bin tim cn in cm, cm bi

hnh 2.78 bao gm phn to in tr

l mch dao ng, mch pht hin v

hai dng NPN hay PNP

Bin & Chuyn i

in cm to ra vng

n i tng c cht

vt.

n dung.

phn: in cc ni

y nh hnh 2.77.

n tim cn loi in

ng cu to gm hai

ch ng ra thng


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o B phn cm bi

o Mch dao ng

o Mch ghi nhn

o Mch in ng

c. Nguyn l hot Cm bin ti

i in dung gia

Hnh 2.80

Cm bin m

gia cht lu v kh

Chng 2: Cm

Trang 70

nh 2.78 Cc thnh phn ca cm bin d

Hnh 2.79 Cc in cc cm bin dung.

n (cc bn cc cch in)

n hiu

ra

g

cn in dung pht hin theo nguyn t

t cm bin v u cm bin), c th ph

Nguyn tc hot ng cm bin tim cn

in dung hot ng da trn s khc b

ng kh. iu kin cn thit p dng

Bin & Chuyn i

ng.

c tnh in (s thay

t hin tt c cc vt.

loi in dung.

it hng s in mi

phng php ny l


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Trang 71

hng s in mi ca cht lu phi ln hn hng s in mi ca khng kh,

thng l gp i. Hng s in mi ca khng kh l 1.0; du c hng s in

mi t 1,8 n 5; nc c hng s in mi gia khong 50 n 80.

Khi mc cht lu thay i th hng s in mi cng thay i tng ng.

Mt loi t in c gi l cu in dung o ton b in dung v cho tn hiu

o lin tc.

T in gm hai bn cc bng kim loi t cch nhau qua vt liu in mi.

Cm bin dung l t in m: Gm hai bn cc t hng ra pha trc nh

hnh 2.81

Hnh 2.81 Hai loi cm bin tim cn loi in dung.

B mt cm bin l mt bn cc. Khi c in p xoay chiu t vo b mt

to ra mt in trng bin thin. in p ny ly im t nh mc chun

T in gm hai bn cc v cht in mi gia. Khong cch gia hai

in cc nh hng n kh nng tch tr in tch ca mt t in (in dung l

i lng c trng cho kh nng tch tr in tch ca mt t in). Nguyn tchot ng ca cm bin tim cn loi in dung da trn s thay i in dung

khi vt th xut hin trong vng in trng. T s thay i ny trng thi On

hay Off ca tn hiu m ng ra s c xc nh. Mt bn cc l thnh phn

ca cm bin, i tng cn pht hin l bn cc cn li. Mi quan h gia bin

sng dao ng v v tr i tng cm bin tim cn in dung tri ngc so

vi cm bin tim cn in cm. Hnh 2.82


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Trang 72

Hnh 2.82 Hot ng ca cm bin tim cn in dung

Hnh 2.83 Sng dao ng mch dao ng cm bin in cm v in dung

Cm bin tim cn loi in dung c th pht hin bt c loi i tng no

c hng s in mi ln hn khng kh. Vt liu cng c hng s in mi cng

cao th cng d c cm bin pht hin. V d nc v khng kh, cm bin

tim cn in dung rt d dng pht hin ra nc (hng s in mi = 80) nhng

khng th nhn ra khng kh (hng s in mi = 1). i vi cc cht kim loikhc nhau, kh nng pht hin ca cm bin l khng i. Nhng i vi cc

cht khc, th phm vi pht hin ca cm bin i vi tng cht l khc nhau. V

vy, cm bin tim cn in dung c th dng pht hin cc vt liu c hng

s in mi cao nh cht lng d n c cha trong hp kn (lm bng cht liu

c hng s in mi thp hn nh thy tinh, plastic). Cn chc chn rng i

tng cm bin pht hin l cht lng ch khng phi hp cha.


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Trang 73

Hnh 2.84 Cm bin in dung pht hin cht lng trong bnh cha.

Khi cha c vt gia hai bn cc: Hnh 2.85

Hnh 2.85 Khi khng c vt th gia hai in cc

o in dung gia hai bn cc:

d

AC r

0= (2.14)

r :Hng s in mi gia hai bn cc.

0: Hng s in mi chn khng. ( mF/10.854187.812

0= )

o Nu khng c vt th gia hai bn cc:

d

ACr

0;1

== (2.15)

Nu gia hai bn cc tn ti vt th khng dn in:Hnh 2.86


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Trang 74

Hnh 2.86 Khi c vt th (phi kim loi) gia hai in cc


d

AC r

0= (2.16)

o Khi c vt th gia hai bn cc th: >1r C s tng

Do s tng gi tr ca C c s dng pht hin vt th.

Nu tn ti vt th kim loi gia hai bn cc dn in:Hnh 2.87

Hnh 2.87 Khi c vt th (kim loi) gia hai in cc


ed

AC r

=

0 (2.17)


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Trang 75

o V mi trng gia hai bn cc l khng kh nn:

ed

ACr

== 01

(2.18)

S c mt ca vt dn in gia hai bn cc cng lm in dung tng

Trong trng hp in cc th hai cch ly vi mt t:

o Nguyn tc nh cc trng hp trn.

o Cn tm ng lin kt bn cc vi im ni t.

Hnh 2.88 Khng c in cc tip t

o Nu khng c ng ni t cho bn cc th 2.

o in cc t ni trc tip trn b mt cm bin. iu ny to ra mt in

trng c lp vi im cc t.

d.Phn loi cm bin in dungCm bin tim cn in dung cng phn thnh 2 loi: shielded (c bo

v) v unshielded (khng c bo v).

o Loi c bo v c vng kim loi bao quanh gip hng vng in trng v

pha trc v c th t ngang bng vi b mt lm vic.

o Loi khng c bo v khng c vng kim loi bao quanh v khng th t

ngang bng vi b mt lm vic. Xung quanh cm bin phi c 1 vng trng

(ging cm bin tim cn in cm loi khng c bo v), kch thc vng

trng ty thuc vo tng loi cm bin.


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e. c im cm bin in dungo C th pht hin st, kim loi, nha, nc, si, g,

o Tui th di v tinh cy cao.

o C mch bo v chng ni ngc cc ngun.

o D dng iu chnh khong cch bng volume. iu chnh c nhy bn

trong.

o C th kim tra tnh trng hot ng bi ch th LED .

o D dng kim tra mc v v tr.

f. Nhng yu t nh hng n tm pht hin ca cm bin tim cn in dungo Kch thc ca in cc ca cm bin.

o Vt liu v kch thc i tng.

o Nhit mi trng.

i tng tiu chun v hng s in mi

i tng tiu chun c ch nh ring vi tng loi cm bin tim cnin dung. Thng thng cht liu ca i tng tiu chun c nh ngha l

kim loi hoc nc.

Hnh 2.89 i tng tiu chun v hng s in mi ca cm bin in dung.


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Trang 77

Hnh 2.89 Biu din mi quan h gia kh nng pht hin i tng v

hng s in mi.

g. u im v nhc im ca cm bin tim cn in dung u im:

o C th cm nhn vt dn in v khng dn in.

o Tnh cht tuyn tnh v nhy khng ty thuc vo vt liu kim loi.

o N c th cm nhn c vt th nh, nh.

o Tc hot ng nhanh.

o Tui th cao v n nh cng cao i vi nhit .

Nhc im:

o B nh hng bi m

o Dy ni vi sensor phi ngn in dung dy khng nh hng n b

cng hng ca b dao ng.

2.7.2.2 Cc i lng cn ch khi s dng

a. iu chnh nhyKhi khng c mc tiu pht hin, hay khi c s dao ng gia khong cch

gia cm bin v vt. Ty theo tng loi vt v loi cm bin m ta c th chnh

cho ph hp (xem ch dn ca nh sn xut)

b. S giao thoa v nh hng bi kim loi xung quanhKhi c nhiu cm bin tim cn c t st nhau, s lm vic sai ca cc

cm bin c th do nguyn nhn ca s giao thao ln nhau. V th ta phi quy

nh mt khong cch nh gia 2 cm bin nh cc hnh 2.90

Hnh 2.90 Cc cch iu chnh nhy.


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Trang 78

Khi cc cm bin c t trn cc bng kim loi, n i hi che chn cm

bin trnh nh hng bi cc vt bng kim loi ngoi tr vt cn pht hin.

V th ta phi quy nh mt khong cch nh gia 2 cm bin nh hnh 2.91

Hnh 2.91 Cc cch che chn cm bin.

c. nh hng ca cc loi vt liuo Vt liu ca vt cm bin:Khong cch cc cm bin c th khc nhau bi

cc c trng in ca vt cm bin (tnh cht dn in, hng s in mi) v

tnh trng ht nc, kch thc.

o in trng c tn s cao:N c th gy ra s c cho my mc m cc my

ny pht ra tn s cao ca in trng v d nh my git

o Mi trng xung quanh: C nc hoc du trn b mt cm bin hay cc

chai pht hin mc b ph du n c th gy ra trc trc. c bit loi c

ng knh nh (15mm) c nhy cao vi cc vt c in cm ta phi ch

ng b thm nc.

o Du: khng cho du chy vo cm bin nht l i vi loi v lm bng

nha.

d. S tip tKhong cch cm bin s c thay i bi tnh trng tip t ca cm bin

tim cn loi in dung v vt [50x50x1mm(st)]. Phi kim tra vt liu trc

khi lp n vo bng.


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2.7.3 Cm bin siu m: (Ultrasonic sensor)

2.7.3.1 Khi nim sng siu m

Siu m l sng c hc c tn s ln hn tn s m nghe thy (trn 20kHz).

Thnh gic ca con ngi rt nhy cm vi di tn s t m trm (vi chc Hz)

n cc m thanh rt cao (gn 20kHz). Mt s loi vt nh di, ong c th cm

nhn c siu m.

Gii thiu v cm bin siu m: Cm bin siu m l thit b dng xc

nh v tr ca cc vt thng qua pht sng siu m. Cm bin siu m c th pht

hin ra hu ht cc i tng l kim loi, phi kim, lng hoc cht rn, vt trong

hoc m c (nhng vt c h s phn x sng m thanh ln).

2.7.3.2 Nguyn l ch to

Sng siu m c truyn i trong khng kh vi vn tc khong 343m/s.

Nu mt cm bin pht ra sng siu m v thu v cc sng phn x ng thi o

c khong thi gian t lc pht i ti lc thu v th my tnh c th xc nh

c qung ng m sng di chuyn trong khng gian. Qung ng di

chuyn ca sng s bng 2 ln khong cch t cm bin ti chng ngi vt, theohng pht ca sng siu m. Hay khong cch t cm bin ti chng ngi vt

s c tnh theo nguyn l TOF (Time Of Flight) hnh 2.92

Hnh 2.92 Nguyn l TOF.


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Cm bin m

gian t lc truyn s

m s dng sng

trong khng kh

bnh cha.

Hnh 2.94 Mt v

2.7.3.3 Gii thiu cm

a. Cu toCm bin tim cn

o B phn pht v

o

B phn so sno Mch pht hin

b phn so sn

nhn v vn tc

o Mch in ng

hiu t cm bi

Chng 2: Cm

Trang 80

Hnh 2.93 Cc loi cm bin siu m.

sng siu m c xc nh mc bng

ng ti lc nhn c sng phn hi. C

di tn s hn 10 KHz. Tc truyn

150C) ph thuc vo loi kh v nhit

i loi cm bin tim cn siu m do Siem

bin siu m

iu m c 4 phn chnh:

nhn sng siu m (Transducer / Receiv

(Comparator)(Detector Circuit): Khi cm bin nhn

h tnh ton khong cch bng cch so

m thanh.

ra (Output): Tn hiu ng ra c th l dig

digital bo c hay khng s xut hin

Bin & Chuyn i

cch o khong thi

bin mc sng siu

a sng (343m/giy

ca kh bn trong

ns sn xut.

er)

c sng phn hi,

nh thi gian pht,

ital hoc analog. Tn

i tng trong vng


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Trang 81

cm nhn ca cm bin. Tn hiu t cm bin analog cha ng thng tin

khong cch ca i tng n cm bin.

Hnh 2.95 Cc thnh phn ca cm bin tim cn siu m.

b. Nguyn l hot ngK thut cm bin siu m da trn c im vn tc m thanh l hng s.

Thi gian sng m thanh i t cm bin n i tng v quay tr li lin h trc

tip n di qung ng. V vy cm bin siu m thng c dng trong

cc ng dng o khong cch. Hnh 2.96

Hnh 2.96 Sng m thanh phn hi khi i tng l cht rn, cht lng.

Tn s hot ng: Nhn chung, cc cm bin cng nghip hot ng vi tn

s 25kHz n 500kHz. Cc cm bin trong lnh vc y khoa th hot ng vi

khong tn s t 5MHz tr ln. Tn s hot ng ca cm bin t l nghch vikhong cch pht hin cm bin. Vi tn s 50 kHz, phm vi hot ng ca cm

bin c th ln ti 10 m hoc hn, vi tn s 200 kHz th phm vi hot ng cm

bin b gii hn mc 1 m.

Vng hot ng: l khu vc gia 2 gii hn khong cch pht hin ln nht

v nh nht. Cm bin tim cn siu m c mt vng nh khng th s dng gn

b mt cm bin gi l khu vc m hay vng cht (blind zone). Hnh 2.97


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Hnh 2.97 Vng hot ng ca cm bin tim cn siu m.

Cm bin siu m bao gm: mt b pht sng m lm bng a gm s s

pht sng lan truyn trong khng gian n khi gp vt cn s c sng di li.

Hnh 2.98

Hnh 2.98 S lan truyn sng m ca cm bin siu m.

Trong mt chu k lm vic cm bin s c lin tc sng di v cho n khi

xung di v c bin bng xung pht i ban u s kt thc mt chu k thu

nhn. Hnh 2.99

Hnh 2.99 Chu k c xung ca cm bin siu m.


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Vng hot ng ca cm bin siu m bao gm: Vng cht, vng nhn thy

v vng ci t trc c (vng hot ng). Hnh 2.100

Hnh 2. 100 Cc vng hot ng ca cm bin siu m.

Khi bt u pht xung l lc sng m s pht i n khi gp vt cn sng s

di li nhng vng hot ng ph hp ch cch u cm nhn ca cm bin

khong 6 n 8 cm vng ny gi l vng cht. Hnh 2.101

Hnh 2. 101 Hot ng ca cm bin siu m

Gc qut ca cm bin siu m l vng mu xanh, cn li l vng m cm

bin khng o c gi l vng m. Hnh 2.102

Hnh 2. 102 Hot ng ca cm bin siu m

Cm bin siu m c m hnh ha thnh mt hnh qut, trong cc

im gia dng nh khng c chng ngi vt, cn cc im trn bin th

dng nh c chng ngi vt hnh 2.103


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Trang 84

Hnh 2.103 Hot ng ca cm bin siu m

2.7.3.4 Sai s nhiu ph bin vi cm bin siu m

a. Hin tng forecastingHin tng Forecasting l hin tng phn x gc sai lch ca cm bin.

Do nguyn l TOF, c khong cch ng, cm bin siu m phi hng

vung gc vi b mt chng ngi vt cn o. Tuy nhin, cc chng ngi vt

khng bao gi l phng, mn, nn tia phn x c th khng tng ng vi gc ti.

Cc chm tia phn x ny c nng lng phn x thp hn nh hnh 2.104.

Hnh 2.104 S phn x ca sng siu m trn b mt vt liu

Tuy vy, mt khong cch no , cm bin siu m vn c th ghi nhn

c nhng tn hiu phn x ny. Kt qu, thng s c v ca cm bin siu m

b lch do gc m ca cm bin siu m ln. Hnh nh v hin tng Forecasting

nh hnh 2.105.


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Trang 85

Hnh 2.105 Hin tng Forecasting

Ngoi ra, v gc m rng nn khng ch sai v nhn dng v tr chng ngi

vt, m khong cch ghi nhn cng b sai lch. Tuy vy, sai s ny khng ngk nh sai s do hin tng c cho gy ra. V sai s ny l sai s c th qun l

c, trong khi , sai s do hin tng c cho khng th qun l c. Sau

y chng ta s tm hiu v hin tng c cho v phng php x l hin

tng c cho.

b. Hin tng crosstalkHin tng c cho (crosstalk) l hin tng m cm bin siu m ny ghi

nhn tn hiu phn x hoc tn hiu trc tip t cm bin siu m khc hoc sau

qu trnh sng siu m truyn i v phn x qua cc b mt quay li cm bin

mt cch khng mong mun. Hnh 2.106 m t hin tng c cho ca cm

bin siu m

Hnh 2.106 Hin tng c cho ca cm bin siu m


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Hin tng c cho c th phn loi thnh hai loi chnh:

o Loi 1l hin tng nhiu robot hot ng trong cng mt mi trng v cm

bin siu m ny ghi nhn tn hiu ca cm bin siu m kia mt cch trc tip

hoc gin tip hoc do sng siu m di chuyn trong khng gian sau mt thi

gian ngu nhin no quay tr li cm bin.

o Loi 2l hin tng cm bin siu m ny ghi nhn tn hiu ca cm bin siu

m kia trn cng robot sau qu trnh phn x.

Cn phi phn bit hai qu trnh c cho ny, bi v ta thy i vi hin

tng c cho loi mt, r rng sng siu m sai lch l ngu nhin, khng d

on c. Tuy nhin, v tnh ngu nhin ny, vic x l nhiu (tn hiu sai t

cm bin khc) tr nn d dng hn thut ton EERUF cho php x l c hai loi

ca hin tng c cho.

tng c bn ca thut ton ny nm ch, xem cc tn hiu ghi nhn

c l nhiu v s dng nhng quy nh pht v thu loi b c cc nhiu

khng hp l.

Phn tch x l hin tng crosstalk

Mc tiu ca vic x l hin tng c cho l nhm nng cao tc c

ca cm bin v on trc c ng c cho khi no xy ra. Ngoi vic xc

nh thi im xy ra hin tng c cho th ta c th pht thm mt cm bin

v ch c cm bin, i mt thi gian t cho nng lng sng m yu dn v

khng lm nh hng ln cc cm bin khc trong cng mt mi trng. hnh

2.107

Hnh 2.107 t lch thi gian pht sng


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Trang 87

Trong hin tng c cho loi 1, nu cc ng c cho hnh thnh ngu

nhin v khng th xc nh trc, ta nhn thy c th s dng phng php lp,

c nhiu ln nhn ra c tn hiu ln u ghi nhn c l tn hiu gy nhiu.

Nh vy vic c cm bin nhiu ln cho php ta loi b c cc ng ccho ngu nhin.

Trong hin tng c cho loi 2 khng phn bit c ng cho ln hai

v ln ba. Chng ta s dng phng php Borenstein pht hin ng c

cho khi n xut hin v thay i cc gi tr thi gian ch sau mi chu k c.

Hnh 2.108

Hnh 2.108 Phng php x l hin tng c cho

c. Sai s do mi trngSai s do nhit i tng cn o, nhit v m mi trng c m

t nh hnh 2.109

Hnh 2.109 nh hng ca nhit i tng cn o


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Khi nhit mi trng thay i cng nh hng n kt qu o, th m

t qu trnh thay i nh hnh 2.110

Hnh 2.110 nh hng ca nhit i tng cn o

Khi m t mi trng thay i cng nh hng n kt qu o, th

m t qu trnh thay i nh hnh 2.111

Hnh 2.111 nh hng ca m mi trng

Nhit b mt ca i tng nh hng n phm vi hot ng ca cm

bin. Hi nng ta ra t i tng c nhit cao lm mo dng sng, lm cho

khong cch pht hin ca i tng ngn li v gi tr khong cch khng chnh

xc.


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Trang 89

Hnh 2.112 nh hng ca nhit i vi sng phn hi.

2.7.3.5 Cc ch khi s dng cm bin siu ma. Cch b tr cm bin

Kch thc v vt liu ca i tng cn pht hin quyt nh khong cch

pht hin ln nht (xem hnh 2.113)

Hnh 2.113 Khong cch hot ng ca cm bin tim cn siu m.

Khi b tr cc cm bin siu m gn nhau khong cch gia cc cm bin cn ch

b tr sao cho tha mn cc iu kin theo cc bng ca tng trng hp nh cho.

o Khi b tr song song hai cm bin khong cch gia chng nh hnh 2.114

o Khi b tr i mt hai cm bin khong cch gia chng nh hnh 2.115

o Khi b tr cm bin gn nhng vt c b mt phn x khc nhau khong cch

gia chng nh hnh 2.116


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Trang 90

Hnh 2.114 B tr song song hai cm bin

Hnh 2.115 B tr mt i mt.

Hnh 2.116 nh hng ca vt so vi vng hot ng

B mt phng phn hi nng lng ca sng m thanh tt hn b mt g

gh. Tuy nhin b mt trn phng i hi khc khe hn v v tr gc to thnh

gia cm bin v mt phng i tng xem hnh 2.117

Hnh 2.117 t cm bin siu m i vi i tng c b mt g gh v

gc nghing so vi phng ngang 3

o

.


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Trang 91

b. u nhc im ca cm bin siu m u im:

o Khong cch m cm bin c th pht hin vt th ln ti 15m.

o Sng phn hi ca cm bin khng ph thuc mu sc ca b mc i tng

hay tnh cht phn x nh sng ca i tng v d b mt knh trong sut, b

mt gm mu nu, b mt plastic mu trng, hay b mt cht liu nhm sng,

trng... l nh nhau.

o Tn hiu p ng ca cm bin tim cn siu m analog l t l tuyn tnh vi

khong cch. iu ny c bit l tng cho cc ng dng nh theo di cc

mc ca vt cht, mc chuyn ng ca i tng.

Nhcim:

o Cm bin tim cn siu m yu cu i tng c mt din tch b mt ti

thiu (gi tr ny ty thuc vo tng loi cm bin).

o Sng phn hi cm bin nhn c c th chu nh hng ca cc sng m

thanh tp m.

o Cm bin tim cn siu m yu cu mt khong thi gian sau mi ln sng

pht i sn sng nhn sng phn hi. Kt qu thi gian p ng ca cm

bin tim cn siu m nhn chung chm hn cc cm bin khc khong 0,1 s.

o Vi cc i tng c mt vt cht thp nh bt hay vi (qun o) rt kh

pht hin vi khong cch ln.

o

Cm bin tim cn siu m b gii hn khong cch pht hin nh nht.o S thay i ca mi trng nh nhit (vn tc m thanh ph thuc vo

nhit ), p sut, s chuyn khng ng u ca khng kh, bi bn bay

trong khng kh gy nh hng n kt qu o.


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Trang 93

trong c vn tc trong chn khng c = 299792km/s, n chit sut ca mi trng

truyn sng

o S lin h gia tn s f v bc sng::

fV=

(2.2)

o Trong chn khng:f

c=

(2.21)

o Tnh cht ht ca nh sng th hin qua s tng tc ca n vi vt cht.nh sng bao gm cc ht photon vi nng lng Wph thuc vo tn

s.W= hf (2.22)

Trong h l hng s Planck h = 6,6256.10-34Js

Trong vt cht cc ht in t lun c xu hng tr thnh in t t do.

gii phng c cc ht in t khi nguyn t th cn 1 nng lng ti thiu

bng nng lng lin kt WL. Do nu photon hp th 1 ht in t th cn 1

iu kin l W WL

o Khi ta c:

h

Wf L

do ta c

f

c= nn

LW

hc

(2.23)

o Bc sng ngng (bc sng ln nht) ca nh sng l bc sng c thgy nn hin tng gii phng in t c tnh t biu thc:

ls Whc= (2.24)

Hin tng gii phng ht dn di tc dng ca nh sng bng hiu ng

quang in gy nn s thay i tnh cht in ca vt liu. y l nguyn l c

bn ca cm bin quang. Di tc dng ca nh sng, hiu ng quang in t l

thun vi s lng ht dn c giiphng trong 1 n v thi gian. Ngay c khi

> Sth khng th gii phng tt c cc ht dn bi v 1 s s phn x t b mt

v s khc s chuyn nng lng ca chng thnh nng lng ca dao ng


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Trang 94

nhit. i vi vt liu c h s phn x R ln v b chiu bi nh sng n sc c

cng sut th:

o S photon chiu n trong 1 giy:

hchvninc

==

(2.25)

o S photon hp th trong 1 giy:

hcRnRn inca

)1()1( ==

(2.26)

o S ht in t v l trng c gii phng trong 1 giy:

hcRnG a

)1(. == (2.27)

Trong l hiu sut lng t (s in t hoc l trng trung bnh c

gii phng khi 1 photon c hp th)

Cc cm bin quang c s dng chuyn thng tin t nh sng nhn

thy hoc tia hng ngoi (IR: Infared) v tia t ngoi (UV: Ultra Violed) thnh

tn hiu in. nh sng c hai tnh cht c bn l sng v ht. Dng sng ca nh

sng l sng in t pht ra khi c s chuyn in t gia cc mc nng lngnguyn t ca ngun sng. Cc dng sng ny di chuyn trong chn khng vi

tc c =299792 km/s (khong 300.000 km/s). Trong vt cht ng sng c vn

tc V = c/n (n l chit sut ca mi trng).

Trn hnh 2.119 biu din ph nh sng v s phn chia thnh cc di mu

ca ph. n v di sng thng dng l m (1m = 1x10-6m).

b. Di ph nh sngCc bc x trng in t tn s cao (tia gamma, tia X v nh sng cc tm)

c bc sng ngn mang nhiu nng lng.


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Hnh 2.119 Tn s v bc sng.

Cc bc x trng in t tn s thp (nh sng thy c, nh sng hng

ngoi, viba) c bc sng ln nhng mang t nng lng hn.

Tia v tia tm cng c phn loi l bc x sng nh sng, nhng l

nh sng khng nhn thy c bng mt thng ca ngi. Ta thy mu nhsng ph thuc di sng.

Tia (IR) c di t 780nm n 106nm, sng nh sng ny c th

thy c di dng nh sng mu ti, sng ny gip cn di ca sng di

v tuyn (LW)

Tia cc tm (UV) c di t 100nm n 380nm, sng nh sng ny c

th thy c di dng nh sng mu tm thm, sng ny gip cn trn ca sngc di ngn hn v c mu nh cu vng.

Ngun sng t nhin hay nhn to l tng hp nhiu dao ng in t, ni

khc i c nhiu di sng khc nhau, qua lng knh ta thy c ph nh sng

ny. Ngun sng nhn to cho php ta dch chuyn phn ln cc bc x ny theo

mun bng cc vt liu v cc tnh cht vt l, chng hn ngun sng ch yu

ch sinh ra tia , tm hay vng.c. n v o quang

Nng lng bc x (Q) l nng lng pht x, lan truyn hoc hp th di

dng bc x, c o bng Jun (J).

Thng lng nh sng () l cng sut pht x, lan truyn hoc hp th, o

bng n v oat (W).

Bc sng

UV-C

nh sng cc tm(Ultra Violet)

(nm)

100 200 300 400 780

UV-B UV-A

nh sng thy c(Visible Light)

nh sng hng ngoi(Infra-Red)

Tm Chm Lam Lc Vng Cam

Violet Indigo Blue Green YellowOrange Red


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Trang 96

(2.28)

Cng nh sng (I) l lung nng lng pht ra theo 1 hng cho trc

di 1 n v gc khi, c n v o l oat/steradian.

=

d

dI

(2.29) chi nng lng: l t s gia cng nh sng pht ra bi 1 phn t

b mt dA theo 1 hng xc nh v din tch hnh chiu ca phn t ny trn

mt phng P vung gc vi hng cosdAdAn= ( l gc gia P v mt

phng cha dA). chi o bng oat/steradian.m

2

.

ndA

dIL=

(2.30)

ri nng lng (E) l t s gia lung nng lng thu c bi 1 phn t

b mt v din tch phn t . ri nng lng c o bng oat/m2

dA

dE

= (2.31)

Tn nh ngha /v th gic /v nng lngLung (thng lng)Cng chi ri

Nng lng

Lumen (lm)Candela (cd)Candela/m2(cd/m2)Lumen/m2hay lux (lx)Lumen.s (lm.s)

Oat (W)Oat/sr (W/Sr)Oat/sr.m2(W/sr.m2)W/m2Jun (J)

d. Ngun sngS dng nh sng c iu ch, tn s thng t 5 n 30kHz. Thng

s dng ph nh sng t mu xanh n nh sng hng ngoi. Hnh 2.120


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Vic s dngsng (ph, thng l

x v vy vic tm h

cm bin.

o n si t wonfratinh hoc thch an

c im: Thng l

qun tnh nhit ln

thp, d v.

o Diode pht quang:thay i theo tn s

theo thi gian. Th

nhc im ca

o Lazer:Tia Lazer lc tnh lin kt mn

sng n sc han t

tia mnh vi n

Phn x nh s

sng phn x s b

Chng 2: Cm

Trang 97

Hnh 2.120 Cng sng v bc sng

1 cm bin ch c hiu qu khi n phng, tn s). Ngun sng s quyt nh

iu ngun sng rt quan trng trong vic

m:c cu to gm 1 dy wonfram c

c cha cht kh him hoc halogen (I

ng ln, di ph rng, c th gim bn

nn khng th thay i bc x 1 cch n

Thi gian hi p nh, khong vi ns

cao. Ph nh sng hon ton xc nh,

ng lng tng i nh (~ 10mW) v

.

ngun sng n sc, chi ln, rt n

h (rt kh xy ra tn sc nh sng). Lazer

on xc nh, thng lng ln, c kh n

hng cao v truyn i vi khong cc

ng trn b mt: Ty theo bng lon

i hng nhiu hay t so vi b mt nh

Bin & Chuyn i

.

hp vi bc x nhi c tnh ca bc

chn la v s dng

v bc bng thy

2). n wonfram c

cc tm lc. Do c

anh chng, tui th

o vy c kh nng

tin cy cao, bn

hy vi nhit l

h hng v c bit

l nh sng c bc

ng nhn c chm

rt ln.

ca b mt m nh

nh 2.121


100/335


Trang 98

Hnh 2.121 Hin tng phn x trn b mt.

Khc x nh sng: Ty theo mi trng c chit sut khc nhau m gc

phn x s khc nhau nh hnh 2.122

Hnh 2.122 Hin tng khc x nh sng.

nh hng ca b mt ln nh sng phn x: Ty theo bng ca b mt

m nh sng chiu vo s phn x nhiu hay t, rng hay hp khc nhau nh

hnh 2.123

mt

ng astvt

Vimt, vt y

Vt thc

AS b khc xtnc nkhngkh

nKhngkh: 1.00nnc : 1.33nthy tinh : 1.46

n1

n2 n1 < n2 n1 > n2

n1

n2

Ngun sng Ngun sngPhn x

Phn x

B mt khuch tn B mt bng long

Ngun sng


101/335


Trang 99

Hnh 2.123 nh hng ca b mt ln nh sng phn x.

2.7.4.3 Cc cm bin quang dn dnga. in tr quang: (Photo Resistor)

Cc cm bin in tr l s ph thuc ca in tr vo thng lng bc x

v ph ca bc x . Quang tr l 1 trong nhng cm bin c nhy cao.

Nguyn tc ch to quang tr l da trn hin tng quang dn do kt qu ca

hiu ng quang in ni (hin tng gii phng ht ti in trong vt liu di

tc dng ca nh sng lm tng dn in ca vt liu).

Cu to: Cm bin quang thng c cu to bng cc cht bn dn a tinh thng nht hoc n tinh th, bn dn ring hoc bn dn pha tp cht.

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.

Ty theo cht cu to m quang tr c vng ph lm vic khc nhau.

in tr: Mt quang tr c gi tr in tr tng ng vi 2 in tr ghp songsong gm in tr ti Rco v in tr sng (quang dn) Rcp c xc nh bihiu ng quang in do nh sng tc ng. Gi tr in tr ti ph thuc vo vt

liu cu to, dng hnh hc, kch thc v nhit .

Cc cht PbS, CdS, CdSe c gi tr in tr ti kh ln: t 104n 109nhit 250C.

Cc cht SbIn, SbAs, CdHgTe c gi tr in tr ti kh nh: t 10n103 nhit 250C

in tr Rcpc xc nh theo biu thc:

Ngun sng

Phn x

B mt khuch tn B mt bng long

Ngun sng

Phn x

gun sng

Phn x

B mt kim loi B mt trong sut

Ngun sng

Phn x


102/335


Trang 100

= aRcp (2.32)

trong a ph thuc vo vt liu, nhit v ph bc x nh sng c gi tr t

0.5 n 1

Do gi tr in tr ca quang tr l RC

+=

+=

aR

aR

RR

RRR

co

co

cpco

cpcoC

.

(2.33)

Thng thng Rcp


103/335


Trang 101

Gcpl quang dn aRG

cpcp

==

1

(2.36)

Khi lm vic quang tr c phn cc bng 1 in p V, khi s c 1

dng in i qua n c xc nh:

POCPCOc IIVGVGVGI +=+== (2.37)

trong Iodng ti, Ipdng quang in

Tuy nhin trong iu kin s dng Io


104/335


Trang 102

i cn phi c mch o ph hp, ngha l phi c cp dng khng i v

ghp theo s o in th, s cu Wheatstone hoc mch khuch i thut

ton. Trong thc t thng c ng dng 2 trng hp l iu khin relay v

thu tn hiu quang. Hnh 2.125

Hnh 2.125 S ng dng quang trb. Diode Cm Quang (photo diode)Nguyn tc

Khi cho 2 cht bn dn P v N tip xc vi nhau s to nn vng ngho ht

dn ti tip xc

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