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cm bin nhit

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  • Bai 2 Cm bin (SENSOR)

  • 2.1 KHI QUT

    2.1.1 Khi nim

    2.1.2 Phn loi cm bin

    2.1.3 ng cong chun ca cm bin

  • 2.1.1 Khi nim

    Cm bin l thit b dng cm nhn bin i cc i lng vt l khng c tnh cht in cn o thnh cc i lng c th o v x

    l c.

    sensor temperature resistance

  • Cc i lng cn o (M):

    thng khng c tnh cht in (nh nhit , p sut, trng lng)

    tc ng ln cm bin cho ta i lng c trng (S) mang tnh cht in nh (nh in tch, in p, dng in hay tr khng)

    cha ng thng tin cho php xc nh gi tr ca i lng .

    c trng (s) l hm ca i lng cn o (M)

    S = F(M)

    Ngi ta gi (S) l i lng u ra hoc p ng ca cm bin. (M) l i lng u vo hay kch thch ( c ngun gc i lng cn

    o). Thng qua o c (S) cho php nhn bit gi tr (M)

    ch to cm bin ngi ta s dung cc hiu ng vt l

  • 2.1.2 Phn loi cm bin

    Cc b cm bin c phn loi theo c trng sau y:

    Theo nguyn l chuyn i gia p ng kch thch.

    Phn loi theo dng kch thch

    Phn loi theo phm vi s dung

    Phn loi theo thng s m hnh mch thay th

  • Theo nguyn l chuyn i gia p ng kch

    thch

    Hin tng Chuyn i v p ng kch thch

    Vt l - Nhit in; - Quang in; - Quang t

    - in t; - Quang n hi; - T in

    - Nhit t....

    Ho hc - Bin i ho hc ; - Bin i in ho

    - Phn tch ph..

    Sinh Hc - Bin i sinh ho; - Bin i vt l.

    - Hiu ng trn c th sng

  • Phn loi theo dng kch thch m

    thanh

    -Bin pha, phn cc; -Ph; -Tc 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 in trng; - t

    thm

    Quang -Bin, pha, phn cc,ph; -Tc truyn

    -H s pht x, khc x; -H s hp thu, h s bc x

    C -V tr; -lc ,p sut; -Gia tc, vn tc

    -ng sut, cng; -Moment; -Khi lung t trng

    -Vn tc cht lu, nht

    Nhit -Nhit ; -Thng lng; -Nhit dung, t nhit

    Bc x -Kiu; -Nng lng; -Cng

  • Theo tnh nng ca b cm bin

    nhy

    chnh xc

    phn gii

    chn lc

    chnh xc

    tuyn tnh

    Cng sut tiu th

    Di tn

    tr

    Kh nng qu ti

    Tc p ng

    n nh

    Tui th

    iu kin la chn

    Kch thc, trng lng

  • nhay: l gi tr nh nht ca gi tr u vo m cm bin cm nhn c

    nhay ca cm bin gi tr m = m0 l t s gia bin thin u ra ca cm bin x v bin thin u vo m trong ln cn ca m0. Gi s l nhay ca cm bin:

  • phn gii: l i lng bng s thay i nho nht u vo m cm bin cn c th o

    c.

    tr: l thi gian p ng ca cm bin

  • chnh xc:

  • Phn loi theo phm vi s dung

    Kh nng qu ti

    Tc p ng

    n nh

    Tui th

    iu kin la chn

    Kch thc, trng lng

  • Phn loi theo phm vi s dung

    Cng nghip

    Nghin cu khoa hc

    Mi trng, kh tng

    Thng tin, vin thng

    Nng nghip

    Dn dung

    V tru

    Qun s

  • Phn loi theo thng s m hnh mch

    thay th

    Cm bin tch cc hot ng nh mt ngun p hoc ngun dng c biu din bng mt

    mng hai ca c ngun.

    Cm bin thu ng c m t nh mt mng hai ca khng ngun, c tr khng phu thuc

    vo cc kch thch.

  • 2.1.3. ng cong chun ca cm bin

    ng cong chun ca cm bin l ng cong c biu din s phu thuc vo i

    lng in (S) u ra ca cm bin vo gi

    tr ca i lng o (m) u vo.

  • 2.1.3. ng cong chun ca cm bin

    ng cong c biu th biu din bng biu thc i s di dng S = F (M) hoc bng

    th sau y:

    0 0

    s s

    m m

    a) b)

    Hinh 1:ng cong chuan cua cam bien

  • 2.1.3. ng cong chun ca cm bin

    Dng ng cong chun

    Da vo ng cong chun ca cm bin, ta c th xc nh gi tr chun Mi cha bit ca M thng

    qua gi tr o c Si ca S

    d s dung, ngi ta thng ch to cm bin c s phu thuc tuyn tnh gia i lng u ra

    v u vo, phng trnh S = F(M) c dng S =

    AM+B vi A,B l cc h s, ng cong chun l

    ng thng

  • 2.1.4. Cc nguyn tc ch to cm

    bin Hiu ng ha in:

    Mt s tinh th gi l tinh th ho in (vd nh tinh th sulfate triglycine), c tnh phn cc in t pht phu thuc vo nhit .

    Khi tinh th ho in hp thu nh sng, nhit ca n tng ln lm thay i phn cc in.

    Hiu ng ha in c s dung ch to cm bin o thng lng bc x ca nh sng.

  • Hiu ng p in:

    Khi tc ng mt lc c hc ln mt vt lm bng cht p in (V du nh Thch anh), s lm cho vt b bin dng

    v lm xut hin trn hai mt i din ca vt mt lng

    in tch bng nhau nhng tri du.

    Hiu ng ny c dng ch to cc cm bin o lc, o p sut, gia tc

  • Hiu ng cm ng in t:

    Khi mt thanh dn chuyn ng trong t trng s xut hin mt sc in ng t l vi bin thin ca t thng

    ngha l t l vi tc chuyn ng ca thanh dn.

    Hiu ng in t c ng dung ch to cm bin o tc dch chuyn ca vt thng qua vic o sc in ng

    cm ng.

  • Hiu ng quang in:

    Bn cht ca hiu ng quang in l hin tng gii phng cc ht dn t do trong vt liu di tc

    dung ca bc x nh sng.

    ng dung ch to cm bin quang

  • Hiu ng HALL: 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

    nh trn

    KH l h s phu thuc vo vt liu v kch thc hnh hc ca tm vt liu

  • Hiu ng Hall c ng dung 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 Vh o c gia 2 cnh tm bn dn l hm phu thuc vo v tr ca vt trong khng gian

  • Cc nguyn tc ch to cm bin

    thu ng Cm bin thu ng thng c ch to t

    mt tr khng c cc thng s ch yu nhy

    vi i lng cn o.

    Gi tr ca tr khng phu thuc kch thc hnh hc, tnh cht in ca vt liu ch to

    (in tr sut , t thm, hng s in mi)

  • 2.2 Cc loi cm bin thng dung

    2.2.1 Cm bin nhit

    2.2.2 Cc thut ng thng s dung

    2.2.3 Cm bin tim cn cm ng

    2.2.4 Cm bin tim cn in dung

    2.2.5 Cm bin quang

    2.2.6 Cc ng dung cm bin trong cng nghip

  • 2.2.1. Cm bin nhit

    Cp nhit in (Thermocouple)

    Nhit in tr kim loi (RTD)

    Thermistor

    IC

  • Cp nhit in

    Cu to: gm 2 kim loi khc nhau c hn chung vi nhau

    Mt u gi l u nng

    Hai u cn li khng hn chung gi l u lnh hay u chun.

  • Cp nhit in

    Nguyn l hot ng: khi c chnh lch nhit gia u nng v u lnh ca cp nhit th ng ra ca thermocouple

    s xut hin sc in ng e phu thuc vo chng lch nhit

    v phu thuc vo bn cht ca vt liu dng ch to cm bin.

    Xt mt cp nhit c ch to t 2 kim loi A v B:

    Trong h s K c th xc nh bng thc nghim bng cch o sc in ng ca cm bin nhit bit

    Dy ni

  • Cp nhit in

    u im: Bn, o nhit cao

    Khuyt im: Nhiu yu t nh hng lm sai s. nhy khng cao.

    Thng dng: L nhit, mi trng khc nghit, o nhit nht my nn,

    Tm o: -100 0C

  • Cp nhit in

    Phn loi

  • Cp nhit in

    c tnh vo ra ca mt s cp nhit in

  • Cp nhit in

    Ch :

    - Sc in ng nhit in sinh ra trn Thermocouple phu thuc vo hiu

    s ca nhit u nng T1 v nhit u lnh T2 v vy khi o nhit

    dng thermocouple, ta phi gi nhit u lnh khng i.

    - Tuy nhin nhit u lnh T2 thng chnh l nhit mi trng nn

    vic gi c nh rt kh v vy ngi ta thngdng bin php loi b s

    nh hng ca nhit u lnh bng cch b nhit.

  • Khng nn ni thm dy (v tn hiu cho ra l mV ni s suy hao rt nhiu)

    V tn hiu cho ra l in p ( c cc m v dng ) do vy cn ch k hiu lp t

    vo b khuch i cho ng.

  • Cp nhit in

    Mch o:

    Vo = ?

  • Chn sao cho

  • Nhit in tr kim loi

    Cu to: Cm bin nhit in tr kim loi gm mt dy dn bng kim loi nh: Platin, Niken,

    ng qun trn mt li cch in.

  • Nhit in tr kim loi

    Nguyn l hot ng: Khi nhit ca cm bin thay i, in tr ca cm bin thay i theo phng trnh:

    T o bng oC

    R(T) l in tr ca cm bin nhit T

    R0l in tr ca cm bin 0oC

    A, B, C l cc hng s v c xc nh bng cch o in tr ca cm bin ti cc nhit bit trc

  • Nhit in tr kim loi

    nhit thp, phng trnh chuyn i ca cm bin l tuyn tnh

    Vi l h s nhit ca in tr, tu thuc vo kim loi nh bng sau:

  • Nhit in tr kim loi

    Do tnh cht ca cc kim loi dng ch to cm bin c tnh cht l ho khc nhau nn

    tm o ca cc cm bin s dung cc kim loi

    khc nhau cng khc nhau.

  • Nhit in tr kim loi

  • Nhit in tr kim loi

    Mch o:

    Gi Rx = R + R l in tr ca cm bin,

    Vi R l in tr ca cm bin 0oC

    Chn R1 = R3; R2 = R4

  • Nhit in tr bn dn

    Cu to: Lm t hn hp cc oxid kim loi: mangan, nickel, cobalt,

    Nguyn l: Thay i in tr khi nhit thay i

    u im: Bn, r tin, d ch to.

    Khuyt im: Dy tuyn tnh hp.

    Thng dng: Lm cc chc nng bo v, p vo cun dy ng c, mch in t.

    Tm o: 50

  • Nhit in tr bn dn

    Phn loi:

    H s nhit dng PTC- in tr tng theo nhit .

    H s nhit m NTC in tr gim theo nhit (thng dng)

    Thermistor ch tuyn tnh trong khong nhit nht nh 50-150 0C do vy ngi ta t dng dng lm cm bin

    o nhit.

    Ch s dung trong cc muc ch bo v, ngt nhit, thng gi l Tt-mt.

  • Nhit in tr bn dn

    Lu khi s dng:

    Nn p cht vo b mt cn o

    Trnh lm hng v bo v

    V bin thin in tr nn khng quan tm chiu u dy

  • Mch o

  • IC

  • IC

    Cu to: Cm bin nhit IC l nhng loi cm bin c ch to t nhng cht bn dn. (C cc loi nh Diode,

    Transistor)

    Nguyn l: da trn mc phn cc ca cc lp P-N tuyn tn