Bài giảng kỹ thuật cảm biến phần 4 : Cảm biến nhiệt độ

Bi ging

K Thut Cm Bin (sensors)

1

Hoang Si Hong

----2011----

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

Hanoi, VietNam

Hoang Si Hong-HUST

3

Ngun tham kho

Note: Bi ging mn hc ny c tham kho, trch dn v lc dch t cc ngun sau:

Sch

- K thut o lng cc i lng in tp 1, 2- Phm Thng Hn, Nguyn Trng Qu.

- Cc b cm bin trong o lng-L Vn Doanh

- Cc b cm bin-Nguyn Tng Ph

- o lng in v cc b cm bin: Ng.V.Ho v Hong S Hng

- Sensor technology handbook (edited by JON WILSON)

- Elements of Electronic Instrumentation and Measurement (Prentice-Hall Company)

- Sch gii thch n v o lng hp php ca Vit Nam

Bi ging v website:

- Bi ging k thut cm bin-Hong S Hng-BKHN(2005)

- Bi ging Cm bin v k thut o:P.T.N.Yn, Ng.T.L.Hng BKHN (2010)

- Bi ging MEMs ITIMS BKHN

- Mt s bi ging v cm bin v o lng t cc trng i hc KT khc Vit Nam

- Website: sciendirect/sensors and actuators A and B

Hoang Si Hong-HUST 2

Ni dung mn hc v mc ch

Ni dung Chapter 1: Khi nim chung v Cm bin (2b)

Chapter 2: Cm bin in tr (2b)

Chng 3: Cm bin o nhit (2b)

Chng 4: Cm bin quang (2b)

Chng 5: Cm bin tnh in (2b)

Chng 6: Cm bin Hall v ho in

Chng 6: Cm bin v PLC(1b)

Mc ch: nm c cu to, nguyn l hot ng v ng dng ca

cc loi cm bin thng dng trong cng nghip v i sng. Nm

c xu th pht trin chung ca cng ngh cm bin trn th gii.



Chng 3: Cm bin o nhit

Ni dung Khi nim chung

Nhit k gin n

Cm bin cp nhit in (Thermocouple)

Cm bin nhit in tr (RTD)

Cm bin nhit da trn tnh cht ca diot v tranzito

Ho k

Surface acoustic wave (SAW) v dao ng thch anh

Bao nhiu ?


Khi nim


Nhit k gin n dng cht rn


Nhit k gin n dng cht lng


Cm bin cp nhit in

Nguyn l:

- Hiu ng thomson: vi vt liu ng nht A, trn n c hai im phn bit

khc nhau l M v N c nhit tng ng l t1 v t2, th gia chng s

xut hin mt sut in ng emn = tch phn (t t1->t2) ca dt, trong

l h s vt liu thomson cho trc

- Hiu ng Peltier: hai vt liu Av B khc nhau tip xc vi nhau ti mtim no th xut hin mt sut in ng eAB(t)

M

(t1)

N

(t2)A

A Bt


Cm bin cp nhit in

Nguyn l:

- Hiu ng seebeck: kt hp hai hiu ng ni trn -> xut hin sut in ng

nhit in eT(t) = tch phn t t1 n t2 ca (A B) dt + eKM(t) eJN(t)

- Trong A , B l h s vt liu thomson ca hai vt liu A, B tng ng.

t1 < t2 l nhit tng ng ti hai im khc nhau.

- Nu gi nhit mt u khng i bng khng C (0oC) (nhit u t

do) th xut hin sut in ng ra mt chiu u cn li (u lm vic,

nhit t) t l vi nhit : ET (t) = f(t) t1

M K

N J

t2


Vt liu ch to


Cu to

(hn im v cch li hnh vy c)


Cu to


Chng loi

Hoang Si Hong-HUST16

c tnh


Cc nguyn nhn gy sai s

- Sai s do nhit u t do thay i. Khi khc , u t do c t mi

trng khng C, nhng trong thc t nhit u t do khc khng C

- Sai s do s thay i in tr ng dy, cp nhit hoc ch th

- Sai s do t khng ng v tr, hng hoc din tch tip xc qu b. Thng

thng ngi ta a chiu su ca cp nhit vo mi trng cn o khong

t5-10 ln so vi ng knh dy ca cp nhit.

- Hai dy cp nhit b m c th gy ra sai s ti 20% v in p ra tng gp 10

ln. Nu dy dn khng c v bc chng nhiu v t cm bin trong in

trng ca ng dy cao th (1-5 kV) th n s chu nh hng ca nhiu in

dung v sai s ln n vi %. Chm mt vo ngun 220 VAC sai s c th ln

n 10%.

- Can nhit b t mi hn cng gy ra sai s.

- Chn dy b sai cng c th gy sai s

- ng dng: o nhit , o dng tn s cao, hng chuyn ng, lu tc, p

sut nh..


Mch o


B nhit u t do


nh hng ca in tr mch o


Cm bin nhit in tr

/N: l chuyn i c in tr thay i theo s thay i nhit ca n.


Nhit in tr kim loi

Nhit in tr dy kim loi: thng c ch to t ng,platin v niken vi ng knh dy t 0.02-0.06 mm.


Nhit in tr kim loi


c tnh

- The accuracy of an RTD is significantly better than that of a thermocouple within an RTDs normal

temperature range of 184.44C (300F) to 648.88C (1200F).

Cu tuyn tnh nhng s dng nhit thp

Platinum is the best metal for RTD elements for three reasons.It follows a very linear resistance-to temperature relationship;

it follows its resistance-to-temperature relationship in a highly

repeatable

manner over its temperature range; and it has the widesttemperature range among the metals used to

make RTDs. Platinum is not the most sensitive metal;however, it is the metal that offers the best longterm stability.


Pt100

S khc nhau gia Pt100 (100 , ti 0oC), 500 v Pt1000 ?

The most common type (PT100) has a resistance of 100ohms at 0 C and 138.4 ohms at 100 C. There are also

PT1000 sensors that have a resistance of 1000 ohms at 0 C

and 1385 ohms ti 100C.

Ti sao Platinum c s dng ch yu ch to RTD: biv n c th hot ng n nh trong thi gian di ti mi

trng c nhit cao. Hn na Pt l s la chn tt hn so

vi Cu hoc Ni bi v s tr v mt ho hc ca n v c

kh nng chng li s xi ho .

Mch o c th dng ngun dng, mch cu hoc time 555


Cu to

The Standard Platinum Resistance

Thermometer is fragile and used

only in laboratory environments


Mt s kiu nhit in tr

There are three main classes of Platinum Resistance Thermometers (PRTs): Standard

Platinum Resistance Thermometers (SPRTs), Secondary Standard Platinum Resistance

Thermometers (Secondary SPRTs), and Industrial Platinum Resistance Thermometers

(IPRTs). Table 32.6 presents information about each. (Rugged :chc chn, Fragile: d

gy)


RTD kiu mng mng

The temperature range of thin film platinum elements is 50C (58F) to 400C (752F);

accuracy is from 0.5C (0.9F) to 2.0C (3.6F). The most common thin-film element has

a 100-W ice point resistance and a temperature coefficient of 0.00385C.


Cng ngh sn xut RTD mng mng


Nhit in tr bn dn (NTC-PTC)

large negative temperature coefficient of resistance (NTC)

large positive temperature coefficient of resistance (PTC)

A- hng s ph thuc vo

tnh cht vt l ca bn

dn, kch thc v hnh

dng ca in tr.

- hng s ph thuc vo

tnh cht vt l ca bn

dn

T- nhit tuyt i

e- c s lgarit t nhin

h s nhit ln hn

RTD nhng c tnh phi

tuyn


Cu to nhit in tr bn dn (NTC-PTC)


Sai s v ng dng

Sai s ca nhit k in tr ch yu l do s thay i in trng dy khi nhit mi trng thay i.

in tr ng dy c th t ti 5 trong khi in tr cachuyn i t vi trm .

Ngoi ra dng in chy qua in tr gy nng cng lm cho intr tng v gy ra sai s. Thng chn dng khong vi mA .

ng dng ca RTD,NTD.. ch yu o nhit , o cc i lngkhng in nh o di chuyn, p sut, nng mt s cht kh..


Mch o v chng sai s

B in tr dy khi s dng ngun p

B in tr dy khi s dng ngun dng

Ti sao l nhit in tr 2, 3 v 4 dy ?


Mch o kiu timer 555

Chu k T ca nhp xung ng ra ca time t l vi s bin i R1 (Rx) khi nhit thay i


Mch o dng ngun dng


Cm bin nhit da trn tnh cht bn dn

ca it v tranzito

c tnh ca it ph thuc vo nhit . Da trn c tnh ngi ta onhit hoc s thay i nhit ca mt i tng no . Tuy nhin s

ph thuc ny khng tuyn tnh v khng tin cy, do vy ngi ta s

dng tnh cht ph thuc in p gia bazo-emito ca mt tranzito vo

nhit khi duy tr dng in colecto (Ic) khng i.


Nguyn l


B phi tuyn


IC LM35 hoc LM335


AD590 (Tham kho: bai giang N.N. Tan v Ng.V.Ky)


Ho quang k bc x ton phn


Ho k quang in


Ho k mu sc


o nhit vi cm bin sng m b mt

(SAW-surface acoustic wave)

Content Piezoelectric behavior can be manifested in two distinct ways. Direct piezoelectric effect occurs when a piezoelectric material becomes

electrically charged when subjected to a mechanical stress and conversion ofmechanical energy to electrical energy.

Converse piezoelectric effect occurs when the piezoelectric material becomesstrained when placed in an electric field and conversion of electrical energy tomechanical energy




BWnull

0 dB

M Hz

insertion loss

center frequency (f0)

BW3dB

3dB

Frequency Response

Fig. 7. Temperature dependence of the center frequency of two-port SAW

resonators using AlN/3C-SiC and AlN/Si structures.

Wireless SAW temperature sensor


Principle

- Depending on changes in temperature, the shifts (time

position and phase angle) of the reflection peaks were

modulated.

- The phase angle shift was used to evaluate the sensitivity

because it provides a much higher resolution than the

time shift of the reflection peak.

- All three reflectors showed the same sign of the phase

shifts because the temperature effects are equal on all

the reflectors

Relation between phase different () and temperature (T)

time

2-1

TDC: the temperature coefficient of delay of piezoelectric material

T: measurement temperature

Tref: reference temperature

Cm bin nhit thch anh


Cu hi v Lu


-Nguyn l?

- ng dng?

- B sai s?

- Tnh ton thit k mch o?

Documents

Bài giảng kỹ thuật cảm biến phần 4 : Cảm biến nhiệt độ