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Ging vin: Nguyn c HongB mn iu Khin T ngKhoa in in Ti Hc Bch Khoa Tp.HCMEmail: ndhoang@hcmut.edu.vn

MN HC

CM BIN O NHIT CHNG 3

Ni dung chng 33.1 Nguyn l o nhit 3.2 Thang o v n v3.3 Thermistor3.4 Thermocouple3.5 RTD v cm bin nhit IC

Nguyn l o nhit (tt)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)

Nguyn l o nhit (tt)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

Thang o nhit v n vC 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] + 459.67 Imperial Fahrenheit (F) / Rankine (R) +/- 460 Metric Celsius (C) / Kelvin (K) +/- 273

ThermistorThermistor: in tr nhy vi nhit c s dng o nhit M hnh n gin biu din mi quan h gia nhit v in tr: T = k*R k > 0: thermistor c h s nhit dng (PTC)k < 0: thermistor c h s nhit m (NTC)

Thermistor

ThermistorThermistor NTC c s dng 3 ch hot ng khc nhau:+ Ch in p dng in+ Ch dng in thi gian+ Ch in tr - nhit

ThermistorCh in p dng inKhi thermistor b qu nhit do nng lng ca n, thit b hot 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 bin

c 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 caoThermistorCh 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 nngThermistorCh in tr nhit

a thc bc 3 xp x c tuyn in tr - nhit ca thermistor l phng trnh Steinhart - HartThermistorCh in tr nhit T : nhit thermistor (K)RT : in tr thermistor ()A0, A1, A3 : cc h s c nh sn xut cp

M hnh n gin xp x c tuyn in tr - nhit ca thermistorThermistorCh in tr nhit T : nhit thermistor (K)RT : in tr thermistor () ti TR0 : in tr thermistor () ti T0B : hng s ph thuc vt liu thermistor (thng k hiu BT1/T2 , v d B25/85 = 3540K )

Dng mch cu WheatstoneMch gia cng tn hiu

S dng in tr mc ni tip hoc song songTuyn tnh ha c trng R/T

S dng in tr mc ni tip hoc song songTuyn tnh ha c trng R/T

u nhc im Thermistoru 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

ng dng Thermistor+ 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 ng

V dCho K276 c: B25/100 = 3760KR25 = 11981Tnh in p VNTC khi T = 1000C ?Nhit ca thermistor khi VNTC = 5V ?) Tnh in p VNTC theo RT?

V dTnh in p V0 ?Bit : R25 = 1.0K, B25/100 = 4000K, T = 800CNu V0 = 3V, vy nhit thermistor = ?

V dTnh in p V0 theo Rt ?

Khi 2 kim loi khc nhau c ni 2 u, mt u t nng th c mt dng in chy trong mchThermocouple

Hiu in p mch h (in p Seebeck) l hm ca nhit v thnh phn ca 2 kim loiThermocoupleKhi nhit thay i nh, in p Seebeck t l tuyn tnh vi nhit : eAB = T: h s Seebeck, hng s t l

VD: Hiu in p Thermocouple loi K ti 3000C = 12.2mVThermocouple

Cc loi Thermocouple

Thermocouple

1.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 nhauCc nh lut Thermocouple

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 Cc nh lut Thermocouple

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 in khco in p ThermocoupleMun tm nhit ti J1 phi bit nhit ti J2

Lp tip gip tham chiu

Lp tip gip tham chiu

Mch tham chiu

Mch tham chiup dng nh lut 2

Mch tham chiuMch tng ngo RT TREF VREFo VV1=V+VREF TJ1

u nhc im Thermocoupleu 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 k

V dCho Thermocouple loi J c nhy = 53V/0CKhi nhit o T = 100 th vn k ch bao nhiu?Nu vn k ch 0.507mV th nhit o T = ?

V dTnh in p V1 v V2 ? Thermocouple loi K c = 40V/0C, Thermistor c R25 = 1.0K, B25/100 = 4000K. Cho nhit Thermocouple 5000C, nhit tham chiu 35 0C

V dTnh in p ti chn AN0 v AN1? Thermocouple loi K c = 40V/0C, Thermistor c R25 = 1.0K, B25/100 = 4000K, Zener c VZ = 2.5V. Cho nhit Thermocouple 5000C, nhit tham chiu 35 0C

V dTnh in p Vout ? Thermocouple loi K c = 40V/0C, Thermistor c R25 = 1.0K, B25/100 = 4000K, Zener c VZ = 2.5V. Cho nhit Thermocouple 5000C, nhit tham chiu 35 0C

Khuch i cng c

RTD (Resistance Temperature Detector) l cm bin nhit da vo hin tng in tr kim loi tng khi nhit tngV d: RTD platin 100.RTDDy platin co h s nhit = 0.0039 //0C RTD platin 100 c in tr ti 00C = 100 v h s nhit = 0.39 /0C

Quan h gia in tr v nhit ca RTD c biu din bng phng trnh n gin sau:RTD

o nhit c tm o ln hay chnh xc cao ta s dng phng trnh Calendar Van Dusen nh sau:RTD

S dng RTD platin 100 o nhit . Nu in tr hin ti ca platin l 110 th nhit o c bng bao nhiu? (so snh kt qu khi s dng 2 phng trnh trn)V d RTD

C 3 pp ni dy c s dngPP ni dy RTD

u nhc im RTDu im+ Rt chnh xc+ n nh+ Tuyn tnhNhc im+ nhy thp+ Cn mch kch dng+ Gi thnh cao

Mch kch dng RTD

Mch ng dng RTD

Hu ht cc cm bin nhit IC s dng tnh cht c bn ca 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 outputCm bin nhit IC

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)Ni dy cm bin nhit IC

y l s ni dy tiu biu cho LM34, LM35, LM45.Ni dy cm bin nhit IC

u nhc im cm bin nhit ICu 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 s v t l vi K, F, C Nhc im+ Tm nhit thp (-55 0C 150 0C)+ Cn mch kch

V dCho IC LM35 c ng ra 10mV/0C. Tnh nhy ng ra Vout.

V dTnh in p ng ra khi nhit o l 5000C, bit nhit cm bin nhit IC l 300C.

V d

Bi tp RTDCho RTD Pt100 c in tr 100 v h s tiu tn nhit = 6mW/K khi trong khng kh v = 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 PD l:

Dng ti a:

Bi tp RTDRTD trong tm tuyn tnh:: cn gi l nhy tng i v ph thuc t0 tham chiu : h s nhit (TCR) c tnh t 2 R ti 2 t0 tham chiu

Bi tp RTDVD: Cho RTD Pt100 c in tr 100 v c = 0.00389//K ti 00C. Tnh nhy v h s nhit ti 250C v 500C? H s nhit gim khi nhit tngGii:

Bi tp ThermistorVD: Tnh nhy Thermistor c B = 4200K ti 00C v 500C H s nhit (TCR) hay nhy tng i Thermistor

Bi tp ThermistorS: Dng in ti a ti 00C (Rmax = 13640). I < 0.8 mA Thermistor 2322 640 90007 c R25 = 12k, R90 = 1.3k v = 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.

Bi tp ThermistorS: 17.8K, 27.13K, 16.43K.Mch khuch i DC c 3 li khc nhau ti 3 nhit khc nhau. Thermistor NTC c R20 = 30K 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 ?

Bi tp ThermistorS dng mch bn di o nhit 200C n 1000C vi phn gii 0.10C, Pt100 c in tr 100 v c = 0.00385//K ti 00C v = 40mW/K. Tnh Rr nu Vr = 5V.

Bi tp ThermistorS dng mch bn di o nhit 200C n 1000C vi phn gii 0.10C, Pt100 c in tr 100 v c = 0.00385//K ti 00C v = 40mW/K. Tnh Rr ng ra c nhy 1mV/0C. Vr = 5V.

Bi tp ThermistorS dng mch bn di o nhit 00C n 500C vi phn gii 0.250C, Pt1000 c in tr 1000 v c = 0.00375//K ti 250C. Tnh R1 , R2 , Rp v Vref ng dng qua cm bin 50V v p ra 0 n 2V.

*p s : 2.4mA v 10mA*p s : 2.4mA v 10mA*p s : 2.4mA v 10mA*p s : 2.4mA v 10mA*p s : 2.4mA v 10mA*p s : 2.4mA v 10mA*p s : 2.4mA v 10mA*p s : 2.4mA v 10mA*p s : Rp >100K, Vref = 45.5mV, R2 = 212.3R1; chn R1 = 100, R2 = 21K *