[BTL] Cảm biến nhiệt độ

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<ol><li> 1. I HC QUC GIA H NI TRNG I HC CNG NGH BI TP LN GVHD: TS. Nguyn Ngc Linh Nhm thc hin: Nhm 3 Khoa: C hc k thut &amp; T ng ha Lp: K57M H Ni, ngy 10/05/2015 ti: Tm hiu v cm bin nhit v ng dng </li><li> 2. Bi tp ln Trang 2 Li m u Trong thi bui cng ngh pht trin nh v bo, ngy cng c nhiu sn phm ra i vi nhng tnh nng a dng, phong ph, v c bit l rt thng minh. Khoa hc pht trin lm cho nhng ngnh khc cng pht trin theo, in hnh l ngnh in t, thng tin, vin thng, c kh ch to, Cc ngnh ny kt hp li vi nhau l tin ca s pht trin cc loi my mc thng minh. Mt h thng my mc thng minh c cu thnh t rt nhiu b phn, cc b vi x l c lp trnh phc tp, cc c cu chp hnh, cc c cu x l cng rt phc tp, C mt b phn v cng quan trng to ln s thng minh khng k n l cc loi cm bin. Nh c cc cm bin, cc robot ngy nay c pht trin nhn bit c cc hnh ng phc tp v d nh tay my nm ly ci cc thy tinh sao cho khng v, hay l h thng t ng ng m ca khi c ngi ra vo cc siu th, C rt nhiu loi cm bin c ch to v s dng theo cc mc ch khc nhau trong i sng nh cm bin cm nhn v nhit , nh sng, m thanh, lc, dng chy, Ty theo mi loi cng vic m mi loi cm bin c cch ch to khc nhau. Mt loi cm bin m chng ta bt gp rt nhiu trong cuc sng hng ngy v ng dng ca n cng v cng rng ri, l cm bin nhit . D dng bt gp nhng loi cm bin ny trong cuc sng nh l nhng my o nhit hin th in t, cc l in tr c iu khin, hay chic ng h lch vn nin, Cm bin nhit c ng dng v cng rng ri v ph bin. Chnh v vy, nhm 3 chng em quyt nh thc hin ti v loi cm bin ny, l tm hiu v cm bin nhit v ng dng trong o nhit n gin. Ni dung chnh ca bi tp ln gm c cc mc sau: Gii thiu chung v cm bin v c im ca chng Nguyn l o c bn ca cm bin Gii thiu v cc loi cm bin thng dng Tm hiu v cm bin nhit Cm bin nhit LM35 v mt mch in ng dng c th. Cc thnh vin ca nhm: STT H v tn M sinh vin Ghi ch 1 Phm Trn Hong 12020162 2 Vn Lc 12020244 3 L Tun Anh 12020004 4 Nguyn Vit Bnh 12020525 </li><li> 3. Bi tp ln Trang 3 Mc lc I. Gii thiu chung................................................................................................................. 3 1. Khi nim ............................................................................................................................ 4 2. Phn loi cm bin ............................................................................................................. 4 3. ng cong chun ca cm bin ...................................................................................... 5 4. Mt s c trng c bn..................................................................................................... 7 II. Nguyn l o ca cm bin......................................................................................... 11 1. Vi cc cm bin tch cc................................................................................................. 11 2. Vi cc cm bin th ng ............................................................................................... 13 III. Gii thiu cc loi cm bin thng dng................................................................ 14 1. Cm bin quang ................................................................................................................ 14 2. Cm bin nhit ............................................................................................................. 14 3. Cm bin o v tr v dch chuyn.................................................................................... 14 4. Cm bin o bin dng ..................................................................................................... 15 5. Cm bin o lc ................................................................................................................ 15 6. Cm bin o vn tc, gia tc v rung............................................................................... 16 7. Cm bin o p sut cht lu........................................................................................... 17 8. Cm bin o lu lng v mc cht lu......................................................................... 17 9. Cm bin thng minh ....................................................................................................... 18 IV. Tm hiu v cm bin nhit .................................................................................. 18 1. S lc cc vn lin quan............................................................................................ 18 2. Cm bin nhit . ............................................................................................................ 20 V. Cm bin nhit LM35 v mt mch in ng dng o nhit ..................... 32 1. Tm hiu v cm bin LM35............................................................................................. 32 2. Mch o nhit dng LM35 kt hp vi IC ADC0808 v vi iu khin 8051. ........... 35 Ti liu tham kho................................................................................................................... 40 </li><li> 4. Bi tp ln Trang 4 I. Gii thiu chung 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 th o v x l c Cc i lng cn o (m) thng khng c tnh cht in (nhit , p sut, khong cch, nh sng, m, ) tc ng ln cm bin cho ta mt c trng (s) mang tnh cht in (in tch, in p, dng in, tr khng) 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): s = f(m) (1.1) Trong cng thc (1.1), s l i lng u ra hoc l phn ng ca cm bin, x 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 kch thch (m). 2. Phn loi cm bin C rt nhiu loi cm bin c ch to v ng dng trong thc t, ta c th phn loi cm bin theo cc c trng c bn nh sau: Theo nguyn l chuyn i gia p ng v kch thch + Hin tng vt l o Nhit in o Quang in o Quang t o in t o Quang n hi o T in o Nhit t + Hin tng ha hc o Bin i ha hc o Bin i in ha o Phn tch ph + Hin tng sinh hc o Bin i sinh ha o Bin i vt l o Hiu ng trn c th sng Theo dng kch thch + m thanh o Bin pha, phn cc o Ph o Tc truyn sng + in o in tch, dng in o in th, in p o in trng (bin, pha, phn cc, ph) o in dn, hng s in mi, + T o T trng (bin, pha, phn cc, ph) o T thng, cng t trng o t thm + Quang o Bin, pha, phn cc, ph o Tc truyn o H s pht x, khc x o H s hp thc, h s bc x + C o V tr o Lc, p sut o ng sut, cng o Moment o Khi lng, t trng o Vn tc cht lu, nht + Nhit o Nhit o Thng lng </li><li> 5. Bi tp ln Trang 5 o Nhit dung, t nhit + Bc x o Kiu o Nng lng o Cng Theo tnh nng ca b cm bin + 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 Theo phm vi s dng + Cng nghip + Nng nghip + Mi trng, kh tng + Thng tin, vin thng + Dn dng + Giao thng + Nghin cu khoa hc + V tr + Qun s Theo thng s ca m hnh mch thay th + Cm bin tch cc c u ra l ngun p hoc ngun dng + Cm bin th ng c c trng bng cc thng s R, L, C, tuyn tnh hoc phi tuyn. 3. ng cong chun ca cm bin ng cong chun ca 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). Da vo ng cong chun ca cm bin, ta c th xc nh gi tr mi cha bit ca m thng qua gi tr o 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, khi phng trnh s = f(m) c dng s = am+b, trong a, b l cc h s, khi ng cong chun l ng thng. Hnh 1. ng cong chun cm bin </li><li> 6. Bi tp ln Trang 6 Cc 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 c s xy dng ng cong chun di dng tng mnh ( 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. Hnh 2. Phng php chun cm bin - 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 th 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 c tin hnh theo hai cch: + Chun trc tip: cc gi tr khc nhau ca i lng o ly t cc mu chun hoc 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 c sn 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. - Chun nhiu ln Khi 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 i lng ny. Trong trng hp nh vy, 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 tr tng uwgns vi im gc m = 0 v s = 0. + o gi tr u ra theo mt lot gi t tng dn n gi tr cc i ca i lng o u vo. + Lp li qu trnh o vi cc gi tr gim dn t gi tri cc i. Khi chun nhiu ln cho php xc nh ng cong chun theo c hai hng o tng dn v o gim dn. </li><li> 7. Bi tp ln Trang 7 4. Mt s c trng c bn a. nhy ca cm bin i vi cm bin tuyn tnh, gia bin thin u ra s v bin thin u vo m c s lin h tuyn tnh vi nhau: s = S.m (1.2) i lng S xc nh bi biu thc s S m 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 : im m s S m (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. Gi tr S thng c cung cp bi nh sn xut tng ng vi iu kin lm vic nht nh ca cm bin. nhy trong ch tnh v t s chuyn i tnh ng chun cm bin xy dng trn c s o cc gi tr si u ra tng ng vi cc gi 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 dc 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 vo im lm vic. i lng ri xc nh bi t s gia gi tr si u ra v gi tr mi u vo c gi l t s chuyn i tnh. i i Q s r m (1.4) T phng trnh (1.4): 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 ta . nhy trong ch ng nhy trong ch ng 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: 0 1( ) cosm t m m t (1.5) Trong m0 l gi tr khng i, m1 l bin , l tn s gc ca bin thin i lng o. u ra ca cm bin, hi p s c dng: 0 1( ) cos( )s t s s t (1.6) + s0 l gi tr khng i tng ng vi m0 xc nh im lm vic Q0 trn ng cong chun ch tnh. </li><li> 8. Bi tp ln Trang 8 + 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 ch ng, 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 m1 ng vi im lm vic c xt Q0, theo phng trnh: 0 1 1 (1.7) Q s S m nhy trong ch ng ph thuc vo tn s i lng o, S = S(f). 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. b. tuyn tnh 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 cc 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 ch ng, 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 (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, da 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 ha. ng thng tt nht Khi chun cm bin, t kt qu thc nghim ta nhn c mt loi 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 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 trong a thc ni suy. Gi s tin hnh chun cm bin vi N im o, phng trnh c dng: s am b Trong , cc h s a, b c xc nh bng cc biu thc sau: 2 2 22 2 ;i i i i i i i i i i i i i N s m s m s m m s m a b N m m N m m lch tuyn tnh i vi cc cm bin khng hon ton tuyn tnh, khi nim lch tuyn tnh c a ra v c xc nh bi lch cc i gia ng cong chun v ng thng tt nht, tnh bng % trong di o. </li><li> 9. Bi tp ln Trang 9 c. Sai s v chnh xc Ngoi i lng cn o, cc b phn trong cm bin 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 nh sau: .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 th thng phn thnh hai loi l 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 iu kin s dng khng tt hoc do ngi o khng hiu bit v h o gy ra. Cc nguyn nhn sai s c th k n l: + 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 qu o. - Sai s ngu nhin: l sai s xut hin c ln v chiu khng xc nh. Nguyn nhn gy ra sai s h thng th c th d on c, nhng khng th d on c ln cng nh du ca n. Cc 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. 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, t ng 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. d. 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 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 hi p c trng cho ch qu ca cm bin v lm 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. Khong thi gian tr khi tng tdm l thi gian cn thit i lng u ra tng t gi tr ban u ca n ln 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...</li></ol>