cam bien ap suat
TRANSCRIPT
Cm bin v thit b o thng minh.
O P SUT BNG P K IN TR I. 1. L thuyt p sut
Khi nim: khi mt cht lng hay kh c cha trong bnh cha, do chuyn ng nhit hn lon, cc phn t vt cht s tc dng ln thnh bnh mt lc. Nu ta xt lc ny trn mt n v din tch ta c khi nim p sut. Nh vy p sut c nh ngha l lc tc dng vung gc ln mt n v din tch v c xc nh theo cng thc sau:P= F S
Trong : F l lc tc dng, c n v l Newton (N); S l din tch b mt b lc tc dng, c n v l m2 Trong h SI p sut c n v l N/m2 n v dn xut ca p sut l pascal (Pa), 1pascal tng ng vi p sut ng dng do lc 1 Newton tc dng ln b mt phng c din tch bng1 m 2 (1Pa=1N/1m2 ). p sut 1Pa tng i nh, trong cng nghip ngi ta thng dng n v p sut l bar (1 bar = 105 Pa). Mt n v cng hay c dng nht l trong y t l mmHg hay torr. o p sut ta c th s dng mt trong cc loi p k sau : p k thy tnh p k c hc. p k pittong. p k in. Trong phm vi ti ny nhm s i su nghin cu v loi p k in. 2. p k in tr lc cng o p sut bng p k in tr Trang : 1
Cm bin v thit b o thng minh.o Nguyn l lm vic: hot ng da trn hiu ng Tenzo (piezoresistive/ strain gauge) o Hiu ng Tenzo l khi dy dn b bin dng c hc th in tr ca n cng thay i o S bin i theo hiu ng Tenzo cn c gi l bin i in tr lc cng.
Hnh 1: Cm bin bin dng (strain gauge) 3. Cm bin p sut in tr: Cu to : Cm bin p sut kiu in tr c cu to gm 1 strain gauge c dn c nh trn mng mng (phn cch phn p sut cao v phn p sut thp) bin dng nh hnh hnh 2. Khi p sut cht lu tc ng ln cm bin phn p sut cao, mng phn cch b bin dng lm cho Strain gauge b bin dng theo. Khi strain gauge b bin dng, in tr ca n s thay i. Strain gauge ny kt hp vi 3 in tr khc to thnh cu Wheatstone nh hnh 3, t ta c c tn hiu in p vi sai ng ra t l vi p sut.
o p sut bng p k in tr
Trang : 2
Cm bin v thit b o thng minh.Hnh 2: Cu to v mt s dng ca cm bin p sut kiu in tr
Hnh 3: S nguyn l ca cm bin.
Phn loi: - Cm bin p sut tuyt i (Absolute) - Cm bin p sut tng i - Cm bin vi sai
(a) Hnh4: (a)Cm bin p sut tuyt i (c)Cm bin p sut vi sai
(b)
(c) (b)Cm bin p sut tng i
Ni chung, c ba loi cm bin ny u hot ng theo nguyn l so snh p sut cn o vi mt p sut khc, thng bit trc, l p sut chun. Vi cm bin p sut tuyt i, p sut cn o c so snh vi p sut ca chn khng, cn cm bin p sut tng i th p sut cn o c so snh vi p sut kh quyn. o p sut bng p k in tr Trang : 3
Cm bin v thit b o thng minh.
Nguyn l hot ng :
Hnh 5 : s hot ng ca mch cm bin. Khi khng c p sut t ln mng, cu in tr trng thi cn bng, in th li ra lc ny l bng 0. Khi c p sut t ln, mng mng s b bin dng, p lc phn b trn mng s b thay i. Do hiu ng p in tr, cc gi tr ca cc in tr trong mch cu b thay i, c th nu cc in tr song song vi cnh mng c gi tr gim i th cc in tr vung gc vi cnh mng s tng gi tr v ngc li. Kt qu l cu s b mt cn bng v in p li ra l khc 0. S thay i gi tr in tr ph thuc vo bin dng ca mng tc ph thuc vo p sut, nn ln ca tn hiu li ra cng ph thuc vo p sut. Bng cch o in th li ra ta c th o c ln tng ng ca p sut tc dng ln mng.
u im ln nht ca cm bin p sut vi c in t l nhy. C th i vi di in p thp, nhy ca cm bin thay i trong khong t 0,1 n o p sut bng p k in tr Trang : 4
Cm bin v thit b o thng minh.3mV/mbar ph thuc dng hnh hc ca mng v cng dng in, trong di p sut t khong vi trm mbar n hng trm bar, nhy thay i t 0,2 n 12,5mV/bar. Mt u im na l kch thc ca cc cm bin ny do ch to theo cng ngh MEMS nn kch thc rt nh, thun tin s dng trong mi thit b.
Cm bin p sut p tr hot ng da trn s thay i ca gi tr p tr gn trn mng cm bin khi c p sut tc ng. T s thay i gi tr ca ca p tr th ta nhn c s thay i ca in p ng ra. a vo ADC c gi tr p sut th ta cn khuch i tn hiu sang tn hiu in p bng b khuch i. ng dng ca cm bin p sut:
Cm bin p sut l mt trong nhng loi cm bin thng dng nht trong cng nghip. Trong y t th cm bin p sut thng c s dng o p sut mu trong ng mch v trong tnh mch.
Vi cm bin p sut c dng o p sut cht lu nh: o p sut cht lng trong ng ng, o p sut kh trong cc ng ng dn kh, o p sut hi trong ni hi Ngoi ra n cn c th c dng o cao trnh ct cht lng thng qua p sut thu tnh.
II. Thit k mch : 1. S khi : Mt mch cm bin hon chnh phc v trong cng nghip c s khi nh sau:
o p sut bng p k in tr
Trang : 5
Cm bin v thit b o thng minh.p Sut
Cm bin p sut
Khuch i
ADC
Hin th ti ch
Module truyn thng
2. Gii thiu cm bin p sut MP3H6115A: MP3H6115A l mt cm bin c tch hp trong mt con chip. Bn trong vi cm bin ny c mt mch khuych i lng cc v mt mng mng in tr mng. Mch khuych i lng cc ny nhm mc ch cho tn hiu u ra mc cao ph hp cho vic iu khin v kt ni vi cc thit b. Mng in tr mng nhm mc ch b nhit. N cung cp mt lng in p rt chnh xc v tuyn tnh t l vi p lc tc dng. Vi cm bin ny li loi vi cm bin kiu p tr nn c cu to ging nh trnh by phn trn. Hnh 6 l s ct ngang ca vi cm bin MP3H6115A.
o p sut bng p k in tr
Trang : 6
Cm bin v thit b o thng minh.
Hnh 6: Vi cm bin p sut MP3H6115A
Hnh 7: S ct ngang ca MP3H6115A Phn b chn ca vi cm bin :
Cc chn 1,5,6,7 v 8 l cc chn kt ni bn trong ca thit b khng kt ni ra ngoi hay cc thit b xung quanh. Vi cm bin ny c 1 chn ngun ra VOUT, mt chn ni t v mt chn ngun nui VS c gi tr l 3V. c tuyn ca MP3H6115A Vi in p ngun cung cp 3 VDC v nhit ca mi trng khong 25C th vi cm bin p sut ny c mt s c tnh nh sau o p sut bng p k in tr Trang : 7
Cm bin v thit b o thng minh.
Mi quan h gia in p u ra v p sut ca MP3H6115A Vi in p ngun cung cp cho vi cm bin l 3VDC v nhit mi trng trong khong t 0-85C th in p u ra ca vi cm bin l t 0-2.75VDC gi tr in p u ra khng nhng ph thuc vo in p u vo m n cn ph thuc vo nhit ca mi trng v nh hng ca nhiu.
Hnh 8 Mi quan h gia in p v p sut ca MP3H6115A
o p sut bng p k in tr
Trang : 8
Cm bin v thit b o thng minh.3. Mch khuch i tn hiu:
Do vi cm bin ny ch c mt u ra nn ta s dng mch khuch i khng o nh sau.
Hnh 7 : Mch khuch i.
Tnh chn linh kin cho khi khuch i :
in p u ra ca vi cm bin c gi tr t 0 2.82 V DC nn a vo ADC ca b vi iu khin PIC ta cn khuych i 5/2.82 = 1.773 ln. Ta c h s khuych i ca mch trn l:
o p sut bng p k in tr
Trang : 9
Cm bin v thit b o thng minh.Do gi tr in p u ra mong mun l t 0 5 V DC nn ta chn R1 l mt in tr cn R2 l mt bin tr vi cc gi tr nh sau. R1 = 4.7 k R2 l bin tr 5 k Chn khuch i thut ton l loi LM 358, c s chn nh sau:
LM358 l khuych i thut ton c c tnh khuch i tt, c h s khuych i cao khong 100dB, c kh nng hot ng vi mt ngun nui hoc l hai nui c di in p rng. Vi ngun n th di in p khong t 3 32V cn vi ngun i th khong 1.5 - 16 V
4. Module ADC, hin th ti ch v truyn thng:
Chng ti gp chung 3 module ny li lm mt v c 3 module u c thc hin trn vi iu khin PIC. thc hin 3 module ny nhm chn VK Pic 16F877A lm vi iu khin chnh.
o p sut bng p k in tr
Trang : 10
Cm bin v thit b o thng minh.VC C D 4
2
5 8
1 4
R 3 2 1 0 k S W 5 1 G N D R R R R R R R R R C C C A A A A A A 0 1 2 0 1 2 3 4 5 1 1 1 1 2 2 2 2 1 Y G N D C 1 5 2 2 0 M 1 3 3 p 1 3 G N D 4 O S S S C S S P I C 1 6 F 8 7 2 / C L 2 3 4 5 6 7 5 6 7 8 3 4 5 6 3 P M R R R R R R R R R R R R R R O V C A A A A A A C C C C C C C C S 0 1 2 3 4 5 0 1 2 3 4 5 6 7 C N _ L R / / / / / / / / / / / / / / 1 * / V A N 0 A N 1 A N 2 A N 3 T 0 C A N 4 P P R / V R / V R K I / C / S S E E R 1 R* / R B 0 R B R B B 3 / F R - /B FR + B BO 6 U / BC 7 2 / 3 / I3 13 23 P 3 C 43 53 P T4 OP 3 N4 T 5 6 G7 V8 9 G0 U G 9 0 1 2 7 8 9 0 R R R R M R R RE R C R T D R P 0R P 1R P 2R P 3R P 4R P 5R P 6R P 7 B B B B B F B B B D D D D D D D D 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
C
1
4
T X R X
T 1 O S O T 1 O S I / C C P 1 S C K / S S D I / S D S D O T X / C K R X / D T 1 / C L K
R/ T D 1 C 0 C C P1 R D R D 2 CR L D 3 RA D 4 R D 5 R D 6 R D 7
/ KP /2 P / P / P / P / P / P / P
1 2I S 2S 2S 2S 2S 2S 3S S
3 3 p
I N R E 0 / R R E 1 / W R E 2 / C K O U T V V D D 7 A
8 D 9 * / A R 1 *0 / A S * / A 1 1 D3 2 D VC C
R E 0 RN E5 1 RN E6 2 N 7
2 1 V V
V
D
K
P
I C
1
6
f 8
7
7
A
ADC : bin i tn hiu t tng t sang s ta dng b ADC c trong vi iu khin PIC. u vo ca ADC nm cc chn A0, A1, A2, A3, A5, E0, E1, E2 ca Pic 16F877A, ta c th chn bt k 1 trong cc chn trn ni vi u ra ca khu khuch i. Khu hin th : nhm s dng 4 LED 7 on hin th cc kt qu o c. Cc tn hiu u vo c ly t port D v cc chn C0, C1, C2, C3 ca port C ca pic 16F87A
o p sut bng p k in tr
Trang : 11
Cm bin v thit b o thng minh.V S C C C C 0 1 2 3 S W D I P - 4 / S M W 4 9 C C V C C V C C V C C
R A R
8 7 1 0 1 5 3
Q 2
6 2 4
R A R
8 6 1 0 1 5 3
Q 2
6 2
3
R A R
8 4 1 0 1 5 3
Q 2
6 2 2
R A R
8 3 1 0 1 5 3
1
1
1
1 Q 2
6 2 1
U V C C
V
6 1 1 C C VC C
U
V
6 1 0 C C VC C
U
V
6 0 9 C C V C C
U
V
6 0 8 C C
H G F E D C B A
H G F E D C B A
H G F E D C B A
D D D D D D D D
0 1 2 3 4 5 6 7
S
W
D
I P
- 8 S
W
4R 8 8 8 R 8 9 R 9 0 R 9 1 R 9 2 R 9 3 R 9 4 R 9 5
Cc in tr s dng trong mch ny l cc in tr hn ch dng qua led nn ta chn gi tr ca chng bng 330 .
Khu truyn thng : Kt qu ca php o s c truyn ln cc cp cao
hn nhm thu thp d liu v thc hin cc php iu khin trong cng nghip. thc hin iu ny th nhm s dng module truyn thng c sn trong PIC theo chun RS232. Hin th ln my tnh: Lp trnh giao din trn Visual Basic. S dng cng COM giao tip gia bo mch vi my tnh. Trn giao din Visual Basic, ta v c th ca p sut. Hin th c s liu ln my tnh t chng ta c th thu thp s liu lu tr nhm mc ch s dng v sau ny. ng thi chng ta cng c th gi cc lnh iu khin xung vi iu khin.
o p sut bng p k in tr
H G F E D C B A
Trang : 12
Cm bin v thit b o thng minh.V C
P11 6 2 7 3 8 4 9 5 C O N N E C T VC C 1 1 1 0 C OV C R u / 5 C 0 1V 7 6 1 18 0 C D B u / 25 7 9 9 1 8 0 0 4 3 T 1 O U R 1 I N V V V +
C C
1
4
U3
16
4 CT C C C
7 2 2 1 1 5 4 + 3 1 +
u
/ 5
0
V C 1 5 1 0 u / 5
0
V
T 2 O U T R 2 O U T G N D
C 1 6 1 0 u / 5 T X D C X D C 6 7
0
V
1 1 T 2 I N T 1 I N1 2 R 2 I NR 1 O U T 15
R
MAX232
Cc gi tr ca cc linh kin trong mch giao tip c chn theo datasheet ca IC MAX232 v c gi tr nh trn hnh.
Chng trnh np vo Pic 16F877A
////////////////////////////////////////////////////////////////////////////////// // // ////////////////////////////////////////////////////////////////////////////////// CHUONG TRINH DOC CAM BIEM AP SUAT // //
#include #DEVICE ADC=10 #include #fuses HS,NOLVP,NOWDT,NOPROTECT
o p sut bng p k in tr
Trang : 13
Cm bin v thit b o thng minh.#use delay(clock=20000000) #use delay(clock=20000000) #use rs232(baud=9600,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8)
#define LED0 PIN_B0 #define LED1 PIN_B1 #define LED2 PIN_B2 #define LED3 PIN_B3 byte const MALED[10] = {0xC0,0xCF,0x64,0x46,0x4B,0x52,0x50,0xC7,0x40,0x42}; //MA LED 0 1 2 3 4 5 6 7 8 9
int8 time=0; float apsuat; int1 TFlag=1; long adc;
#int_TIMER1 void TIMER1_isr(void) { disable_interrupts(global); time++;
o p sut bng p k in tr
Trang : 14
Cm bin v thit b o thng minh.if(time==5) { time=0; set_timer1(3035); delay_ms(1); TFlag=1; } else set_timer1(3035);
enable_interrupts(GLOBAL); }
void hienthi(float32 so) { float32 tam; int nghin,tram,chuc,donvi,point; int16 tem; point=0; if (so>=100) {
o p sut bng p k in tr
Trang : 15
Cm bin v thit b o thng minh.tam=ceil(so*10); point=1; } else if(so>10) { tam=ceil(so*100); point=2; } else { tam=ceil(so*1000); point=3; } tem=(int16)tam; nghin=tem/1000; tem=tem%1000; tram=tem/100; tem=tem%100; chuc=tem/10; donvi=tem%10;
o p sut bng p k in tr
Trang : 16
Cm bin v thit b o thng minh.
output_low(LED0); output_D(MALED[donvi]); delay_ms(5); output_high(LED0);
output_low(LED1); output_D(MALED[chuc]); if(point==1) output_low(PIN_D6);
delay_ms(5); output_high(LED1);
output_low(LED2); output_D(MALED[tram]); if(point==2) output_low(PIN_D6);
delay_ms(5); output_high(LED2);
o p sut bng p k in tr
Trang : 17
Cm bin v thit b o thng minh.output_low(LED3); output_D(MALED[nghin]); if(point==3) output_low(PIN_D6);
delay_ms(5); output_high(LED3); }
void main() { setup_adc(ADC_CLOCK_INTERNAL); setup_adc_ports(ALL_ANALOG); setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1); setup_timer_1(T1_INTERNAL|T1_DIV_BY_8); setup_timer_2(T2_DISABLED,0,1); enable_interrupts(INT_TIMER1); enable_interrupts(GLOBAL);
set_tris_D(0x00);
o p sut bng p k in tr
Trang : 18
Cm bin v thit b o thng minh.set_tris_B(0x00); output_D(0xFF); output_B(0xFF); set_timer1(3035);
int i; long value=0;
while(1) { //SU DUNG TIME DE DOC ADC SAU MOI 1/2S if (TFlag==1) { apsuat=0; value=0; delay_ms(1); //DOC ADC KET HOP VOI LOC NHIEU TAN SO CAO set_adc_channel(0); for(i=0;i>8); putc(adc); enable_interrupts(global);
TFlag=0; } else hienthi(apsuat); } }
III.
Kt qu v nh gi Trang : 20
o p sut bng p k in tr
Cm bin v thit b o thng minh.1. Kt qu: Vic thc hin ti thu c kt qu tt, chng ti thit k c bo mch. Thc hin o th nghim cho kt qu chnh xc c th kt ni vi my tnh thc hin truyn v nhn d liu. Giao din giao tip vi my tnh:
2. nh gi: Vic thc hin ti cho kt qu tt, giao din d s dng v chng trnh d hiu. Tuy nhin do phm vi thc hin ti ch cho php trong mt mn hc v mt s iu kin thc t khng cho php chng ti tip tc thc hin ti vi o p sut bng p k in tr Trang : 21
Cm bin v thit b o thng minh.mc ch ln hn nn bo mch ca chng ti ch cho php lm vic vi mi trng c p sut t 15 115 kPa tng ng vi p sut khng kh (gn 100 kPa).
o p sut bng p k in tr
Trang : 22