Trao i trc tuyn ti:http://www.mientayvn.com/chat_box_li.htmlGing vin: Nguyn c HongB mn iu Khin T ngKhoa in in Ti Hc Bch Khoa Tp.HCMEmail: ndhoang@hcmut.edu.vnMN HCCM BIN O NHIT CHNG 3 3.1Nguyn l o nhit 3.2 Thang o v n v3.3Thermistor3.4 Thermocouple3.5 RTD v cm bin nhit IC Cm bin tip xc: trao i nhit xy ra ch tip xc gia i tng v cm binCm bin khng tip xc: trao i nhit xy ra nh vo bc x, nng lng nhit dng nh sng hng ngoiCm bin b tc ng ca mi trng o, gy ra sai s khi o nhit . Yu cu: cc tiu sai s (thit k cm bin thch hp hoc pp o chnh xc) C 2 pp x l tn hiu nhit :+ Cn bng+ D boPP cn bng: nhit xc nh hon ton khi khng c s sai lch ng k gia nhit b mt o v nhit cm bin, tc l cn bng nhit t n gia cm bin v i tng oPP d bo: cn bng nhit khng t n trong thi gian o, nhit c xc nh thng qua tc thay i nhit ca cm bin C 4 thang o c s dng o nhit + Celsius / Fahrenheit c s dng trong cc thang o hng ngy+ Kelvin / Rankine c s dng khi lm vic vi thang nhit tuyt i (thng c dng trong cc tnh ton khoa hc v k thut)Fahrenheit[F] = [C] 9/5 + 32Celsius[C] = ([F] 32) 5/9Kelvin[K] = [C] + 273.15Rankine[R] = [F] + 459.67ImperialFahrenheit (F) /Rankine (R)+/- 460Metric Celsius(C)/Kelvin(K)+/- 273 Thermistor: in tr nhy vi nhit c s dng o nhit M hnh n gin biu din mi quan h gia nhit v in tr:AT = k*ARk > 0: thermistor c h s nhit dng (PTC)k < 0: thermistor c h s nhit m (NTC)Thermistor NTC c s dng 3 ch hot ng khc nhau:+ Ch in p dng in+ Ch dng in thi gian+ Ch in tr - nhit Ch in p dng inKhi thermistor b qu nhit do nng lng ca n, thit bhot ng ch in p dng in ch ny, thermistor thch hp o s thay i ca iu kin mi trng, v d nh s thay i ca lu lng kh qua cm binc trng dng in thi gian ca thermistor ph thuc vo hng s tiu tn nhit ca v v nhit dung ca phn tKhi cp dng in vo thermistor v bt u t t nng. Nu dng in lin tc th in tr thermistor bt u gimc trng ny c s dng lm chm cc nh hng ca cc gai p caoCh dng in thi gian ch in tr - dng in, thermistor hot ng iu kin cng sut zero, ngha l khng xy ra s t t nngCh in tr nhit a thc bc 3 xp x c tuyn in tr - nhit ca thermistor l phng trnh Steinhart - HartCh in tr nhit 130 1 3ln (ln )T TT A A R A R (= + + T: nhit thermistor (K)RT: in tr thermistor (O)A0, A1, A3: cc h s c nh sn xut cpM hnh n gin xp x c tuyn in tr - nhit ca thermistorCh in tr nhit 01 10BT TTR R e| | |\ .=T: nhit thermistor (K)RT: in tr thermistor (O) ti TR0: in tr thermistor (O) ti T0B: hng s ph thuc vt liu thermistor (thng k hiu BT1/T2, v d B25/85= 3540K )Dng mch cu Wheatstone S dng in tr mc ni tip hoc song song S dng in tr mc ni tip hoc song song u im+ Rt nhy i vi thay i nh+ chnh xc cao (0.020C)+ n nh, tin cyNhc im+ Tm hot ng b gii hn+ Quan h R-T phi tuyn + Trong gia nh: t lnh, my ra chn, ni cm in, my sy tc,+ Trong xe hi: o nhit nc lm lnh hay du, theo di nhit ca kh thi, u xilanh hay h thng thng,+ H thng iu ha v si: theo di nhit phng, nhit kh thi hay l t,+ Trong cng nghip: n nh nhit cho diode laser hay cc phn t quang, b nhit cho cun dy ng,+ Trong vin thng: o v b nhit cho in thoi di ngCho K276 c: B25/100= 3760KR25= 11981OTnh in p VNTCkhi T = 1000C ?Nhit ca thermistor khi VNTC= 5V ?)Tnh in p VNTCtheo RT? 1 k 5 kVo+5V1 kThermistor5 kTnh in p V0?Bit : R25 = 1.0K, B25/100= 4000K, T = 800CNu V0= 3V, vy nhit thermistor = ? Tnh in p V0theo Rt ? 10Vdc0 0R210kR6 5kVo-+321R310kR15k+0RtR510kR410k-R7 5kKhi 2 kim loi khc nhau c ni 2 u, mt u t nng th c mt dng in chy trong mchHiu in p mch h (in p Seebeck) l hm ca nhit v thnh phn ca 2 kim loiKhi nhit thay i nh, in p Seebeck t l tuyn tnh vi nhit : AeAB= oATo: h s Seebeck, hng s t lVD: Hiu in p Thermocouple loi K ti 3000C = 12.2mV1.Dng nhit in khng th to ra trong cc mch ng nht2. Tng i s sc nhit in trong mt mch c cu to t cc cht dn in khc nhau bng 0 nu nhit ti cc ch tip gip nh nhau 3. Nu 2 tip gip ti nhit T1 v T2 to ra in p Seebeck V2, ti nhit T2 v T3 to ra in p V1 th ti nhit T1 v T3 to ra in p l V3 = V1 + V2 Khng th o trc tip ip p Seebeck v:Phi ni vn k vo Thermocouple v chnh cc dy dn vn k to ra mt mch nhit inkhc Mun tmnhit tiJ1 phi bitnhit tiJ2 ( )( )( )1 2 11 11 20: , :J J JJ JV V V t t Tt K T Co o = = = ( )1 REFV T T o = Thay khi Ice Bath bi khi Isothermal p dng nh lut 2 Mch tng ng( )1 REFV T T o = o RT TREF VREFo VV1=V+VREF TJ1 u im+ Gi thnh thp+ n nh c hc+ Tm hot ng rng (-200 0C 2000 0C)Nhc im+ nhy thp (V/0C)+ Cn phi bit nhit tham chiu+ Yu cu calib nh kCho Thermocouple loi J c nhy o = 53V/0CKhi nhit o T = 100 th vn k ch bao nhiu?Nu vn k ch 0.507mV th nhit o T = ?Tnh in p V1 v V2 ? Thermocouple loi K c o = 40V/0C, Thermistor c R25 = 1.0K, B25/100= 4000K. Cho nhit Thermocouple 5000C, nhit tham chiu 35 0CTnh in p ti chn AN0 v AN1? Thermocouple loi K c o = 40V/0C, Thermistor c R25 = 1.0K, B25/100= 4000K, Zener c VZ= 2.5V. Cho nhit Thermocouple 5000C, nhit tham chiu 35 0CTnh in p Vout ? Thermocouple loi K c o = 40V/0C, Thermistor c R25 = 1.0K, B25/100= 4000K, Zener c VZ= 2.5V. Cho nhit Thermocouple 5000C, nhit tham chiu 35 0C RTD (Resistance Temperature Detector) l cm bin nhit da vo hin tng in tr kim loi tng khi nhit tngV d: RTD platin 100O.Dy platin co h s nhit o = 0.0039 O/O/0CRTD platin 100 O c in tr ti 00C = 100 O v h snhit o = 0.39 O/0C Quan h gia in tr v nhit ca RTD c biu din bng phng trnh n gin sau: o nhit c tm o ln hay chnh xc cao ta sdng phng trnh Calendar Van Dusen nh sau:S dng RTD platin 100 O o nhit . Nu in trhin ti ca platin l 110 O th nhit o c bng bao nhiu? (so snh kt qu khi s dng 2 phng trnh trn)C 3 pp ni dy c s dng u im+ Rt chnh xc+ n nh+ Tuyn tnhNhc im+ nhy thp+ Cn mch kch dng+ Gi thnh cao Hu ht cc cm bin nhit IC s dng tnh cht c bnca cc lp tip xc bn dn PN l hm ca nhit .Cc cm bin nhit IC thng dng:+ LM135, LM235, v LM335: 10mV/K output+ LM35 : 10mV/0C output+ LM34 : 10mV/0F output+ AD590 : 1 A/K output y l s ni dy tiu biu cho LM135, LM235, LM335.iu chnh bin tr hiu chnh in p ng ra ti nhit bit (vd: 2.982V ti 25 0C) y l s ni dy tiu biu cho LM34, LM35, LM45. u im+ D dng tch hp vi cc thit b khc+ Gi thnh thp+ Kch thc gn nh+ Ng ra c th in p, dng in hoc sv t l vi K, F, C Nhc im+ Tm nhit thp (-55 0C 150 0C)+ Cn mch kchCho IC LM35 c ng ra 10mV/0C. Tnh nhy ng ra Vout.Tnh in p ng ra khi nhit o l 5000C, bit nhit cm bin nhit IC l 300C.Cho RTD Pt100 c in tr 100O v h s tiu tn nhit o = 6mW/K khi trong khng kh v o = 100mW/K khi nhng trong nc. Tnh dng in ti a qua cm bin gi sai s do t nng dc 0.10C.Gii: Nhit tng khi tiu tn lng cng sut PDl:Dng ti a: 2DP I RTo oA = =TIRo A=RTD trong tm tuyn tnh:o: cn gi l nhy tng i v ph thuc t0tham chiu ( )0 01 R R T T o = + ( ( )100 000100R RCRo=o: h s nhit (TCR) c tnh t 2 R ti 2 t0tham chiuVD: Cho RTD Pt100 c in tr 100O v c o = 0.00389O/O/K ti 00C. Tnh nhy v h s nhit ti 250C v 500C? H s nhit gim khi nhit tng0 0 25 25 50 50S R R R o o o = = =Gii:( )0.00389 /* 100 0.389 / S KKOO= O= O( )( )0 0 0 0250 0250 00.00355 / /1 25 0R RKRR C Co ooo= = = OO (+ ( )500.00326 / / K o = OOVD: Tnh nhy Thermistor c B = 4200K ti 00C v 500C 2TTdR dT BR To = = H s nhit (TCR) hay nhy tng i Thermistor0500.0563/0.0402 /KKoo= = S: Dng in ti a ti 00C (Rmax= 13640O). I < 0.8 mA Thermistor 2322 640 90007 c R25= 12kO, R90= 1.3kO v o = 10mW/K trong nc. Cm bin ny c s dng o nhit nc t 00C v 1000C. Tnh dng in ti a qua cm bin gi sai s do t nng dc 0.50C.S: 17.8KO, 27.13KO, 16.43KO.Mch khuch i DC c 3 li khc nhau ti 3 nhit khc nhau. Thermistor NTC c R20= 30KO v B = 4000K. Tnh cc gi tr in tr: Rs, Rp, RG ti cc nhit 150C, 250C v 350C mch c li tng ng: 0.9, 1.0, 1.1 ?S dng mch bn di o nhit 200C n 1000C vi phn gii 0.10C, Pt100 c in tr 100O v c o = 0.00385O/O/K ti 00C v o = 40mW/K. Tnh Rrnu Vr= 5V. ( )22010001000.1*0.1138.5 930r rrr rrI R V RT CRRR VCR Ro oo| |= = A < |\ . >= O > OS dng mch bn di o nhit 200C n 1000C vi phn gii 0.10C, Pt100 c in tr 100O v c o = 0.00385O/O/K ti 00C v o = 40mW/K. Tnh Rr ng ra c nhy 1mV/0C. Vr= 5V. ( )0 000011925rrrrrrVv R TRdv VS RdT RV RRSooo= + = = = = OS dng mch bn di o nhit 00C n 500C vi phn gii 0.250C, Pt1000 c in tr 1000O v c o = 0.00375O/O/K ti 250C. Tnh R1, R2 , Rpv Vrefng dng qua cm bin 50V v p ra 0 n 2V.