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Bi tp lnK Thut Cm Bin (sensors)

ti: Thit k mch o nhit s

dng cm bin LM335GVHD:TS: Hong S Hng

Thc hin: Nhm etech-3i1. L Hc Phong KT-K53 20081958

2. Bi Quang Sng KT-K53 200821913. H Vn Vng KT-K53 200832224. Nguyn Vn Hng KT-K53 200812315. Hong Danh Vin KT-K53 20083121

1Faculty of Electrical Eng., Hanoi Univ. ofScience and Technology (HUST),


2/27

I. C s l thuyt

Nguyn l: Bin i nhit thnh in p. ogi tr in p trn s bit c gi tr nhit cno.

S khi mch o:

2Faculty of Electrical Eng., Hanoi Univ. ofScience and Technology (HUST),


3/27

Nhim v v hot ng ca tng khi:

Khi cm bin v chun ho tn hiu: c nhimv bin i nhit cn o thnh in p a vo khi chuyn i ADC.

Khi chuyn i ADC: c nhim v bin i

gi tr in p ra t khi cm bin thnh gi trs tng ng a vo khi tnh ton.

Faculty of Electrical Eng., Hanoi Univ. ofScience and Technology (HUST),

3

I. C s l thuyt


4/27

Khi tnh ton v hin th: c nhim v c gitr chuyn i c bi khi ADC v tnh ton

ra gi tr nhit tng ng, sau hin thnhit trn ra LED 7 on.

Khi ngun: Cp ngun cho cc khi hotng. Trong mch s dng ngun in p

chun t bn ngoi, do khng cn thit kkhi ngun cho mch


4

I. C s l thuyt


5/27

1. Cm bin LM335

LM335 l IC tch hp dng o nhit .Nguyn l ca n l da trn mc phncc ca lp chuyn tip p-n tuyn tnh theonhit mi trng. N gm c 3 chn: mt

chn cp ngun (ng thi l chn tn hiura), mt chn ni t v mt chn iu chnh.


5

II. Tm hiu cc linh kin c bn


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6


Cc thng s chnh:

Di o: -40 0C 100 0C

nhy: 10mV / 0K Sai s: 1 0C (Max l 2 0C)

Dng in lm vic:

0,4mA 5mA Tr khng u ra thp

(< 1)


7/27

S kt ni:

Faculty of Electrical Eng., Hanoi Univ. ofScience and Technology (HUST), 7



8/27




9/27

2. ADC0809

ADC0809 l b chuyn i AD 8 bit hot

ng theo nguyn tc chuyn i xp x lintip.

Cc thng s chnh:

phn gii 8 bit. Dn knh vo 8 knh -> x l trc tip bt k

mt trong 8 knh Analog.




10/27

Logic iu khin tng thch cc VXL, VK. Cc u vo gii m a ch c cht.

BUS d liu ra 3 trng thi, c cht. Tc chuyn i nhanh, chnh xc cao,

tiu th cng sut thp. Sai s LSB Cng sut tiu th: 15mW Ngun nui: 5V




11/27

ADC0809 gm 8 knh u voanalog t IN1 ti IN7, ti mi thiim ch lm vic vi 1 knh. 3 tn

hiu C B A dng chn knh. iuchnh in p tham chiu ti 2 chnVref(+) v Vref(-). Chn OE (pin9)dng m b m d liu ra. ChnClock dng cp xung clock choADC0809 hot ng. Start l tnhiu bt u chuyn i v EOC ltn hiu bo kt thc chuyn i




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3. Vi iu khin AT89S52




13/27

1. Khi cm bin v chun hoLM335 c nhy 10mV/0K, ngha l 0 0Cin p ra l 2.73V, do vy ta cn tr i 2.73V in p ra t l vi 0C.

Nu ta chn Uref ca ADC = 5V th phngii ca ADC l 5/256 20mV => phn

gii ca h thng l 20

C. gim phngii ta c th gim Uref v tng nhy choLM335


III. Thit k chi tit tng khi


14/27

y ta chn Uref = 2.56V v tng nhyca LM335 ln 20mV/0C, khi nhy cah thng s l 0,5 0C. Do tn hiu ra cakhi cm bin s l:

Ura= 2(ULM335 -2.73)

=> ta thit k mt mch tr dng OPAM stho mn c yu cu trn.




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S nguyn l:


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2. Khi chuyn i ADC

Theo phn tch trn, Uref ta t bng 2.56V.

Ta dng mt bin tr tinh chnh chnh Urefcho ADC0809. Ta s dng knh 0 lm uvo tng t do C B A = 000, Trong mchs s dng IC NE555 lm mch to xung cp

cho ADC0809. Ta c c s nguyn lca khi nh sau:




17/27

S nguyn l khi chuyn i ADC:




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3. Khi Tnh ton nhit v hin th

S dng VK AT89S52 tnh ton v hin

th nhit ln 4 LED 7 on Anode chung.S dng cng P0 c gi tr chuyn i tADC, cng P1 v P3 K v xut d liuln LED 7 on. P2.0 dng xut tn hiu

Start (bt u chuyn i). S nguyn lca mch nh sau:




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20/27

Xy dng cng thc tnh ton nhit :

phn gii ca khi cm bin l 20mV/0C,

trong khi phn gii ca ADC l 10mV. Do khi nhit tng 1 0C th u ra ca ADCtng 2 n v => nhit t = N/2, N l gi trchuyn i bi ADC. Nhit c th hin th

l ti 0,5 0C.




21/27

S mch in v trongOrcad 9.2




22/27

Di y l mt s nguyn nhn gy ra sai scho mch o v cch gim sai s

Sai s do bn thn LM335 gy ra. Sai s do cc in tr trong mch chun ho

tn hiu. Gim sai s bng cch s dng ccin tr nhiu vch mu c sai s nh, hoc s

dng bin tr tinh chnh v s dng ng ho c chnh xc cao o chnh xc gi trin tr.


IV. Sai s ca h thng o


23/27

Sai s do in p Offset ca cc vi mchkhuch i thut ton. Sai s ny c th gim

bng cch s dng cc vi mch khuch i

thut ton c chn chnh offset. Sai s do vi mch chuyn i ADC0809 to ra. Sai s do in p ngun khng n nh, dn

n cc in p chun cho mch tr, Uref choOPAMP cng khng n nh. Gim bng cchs dng nhng IC n p chnh xc cao.


IV. Sai s ca h thng o


24/27

Sau qu trnh thc hin ti chng em tc nhng kt qu sau:

Thit k thnh cng s nguyn l v s mch in cho mch o nhit .

Thc hin gia cng mch in v lp rp thnhcng mch o nhit trong gii 0 100 0C.

Cc thnh vin trong nhm c thm nhiukinh nghim trong vic thit k cc mch intrn thc t.


V. Kt qu t c


25/27

Trn c s ti o nhit trn chng ta cth m rng theo cc hng nh:

S dng ADC c phn gii cao tng chnh xc cho mch.

S dng ngun dng nui cho cm bin,gip tng khong cch t cm bin ti mch

o. Giao tip my tnh gip cho ngi dng c th

qun l nhit nhiu ni khc nhau.


VI. Cc hng m rng ti


26/27

Kt hp thm mch iu khin nhit v ccthut ton iu khin lm nhit lun gin nh mt nhit nht nh hoc bmtheo mt quy lut no .


VI. Cc hng m rng ti


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Code chng trnh o nhit :

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