H THNG IU KHN PHN TNLecture Notes(Cha cp nht t 8/2003)

TS. Hong Minh Sn B MN IU KHIN T NG, KHOA IN I HC BCH KHOA H NI

MC LC1 NHP MN 1.1 Phm vi cp 1.2 Ni dung chng trnh 1.3 Yu cu kin thc c s 1.4 Tng quan cc gii php iu khin 1.4.1 c trng cc lnh vc ng dng iu khin 1.4.2 Cc h thng iu khin cng nghip CU TRC CC H THNG IU KHIN V GIM ST 2.1 Cu trc v cc thnh phn c bn 2.2 M hnh phn cp 2.2.1 Cp chp hnh 2.2.2 Cp iu khin 2.2.3 Cp iu khin gim st 2.3 Cu trc iu khin 2.3.1 iu khin tp trung 2.3.2 iu khin tp trung vi vo/ra phn tn 2.3.3 iu khin phn tn 2.3.4 iu khin phn tn vi vo/ra phn tn CC THNH PHN CA MT H IU KHIN PHN TN 3.1 Cu hnh c bn 3.1.1 Trm iu khin cc b 3.1.2 Bus trng v cc trm vo/ra t xa 3.1.3 Trm vn hnh 3.1.4 Trm k thut v cc cng c pht trin 3.1.5 Bus h thng 3.2 Phn loi cc h DCS 3.2.1 Cc h DCS truyn thng 3.2.2 Cc h DCS trn nn PLC 3.2.3 Cc h DCS trn nn PC 3.3 Cc vn k thut X L THI GIAN THC V X L PHN TN 4.1 Mt s khi nim c bn 4.1.1 H thng thi gian thc 4.1.2 X l thi gian thc 4.1.3 H iu hnh thi gian thc 4.1.4 X l phn tn 4.2 Cc kin trc x l phn tn 4.3 C ch giao tip 4.4 ng b ha trong x l phn tn 5 5 5 5 6 6 6 8 8 9 10 10 10 11 11 12 12 13 15 15 15 17 18 19 20 21 21 22 25 26 27 27 27 27 28 29 30 31 32

2

3

4

4.4.1 4.4.2 5

ng b ha cc tn hiu vo/ra ng b ha thi gian

2 32 32 33 33 33 34 35 35 36 37 38 38 38 39 40 41 41 44 46 46 48 48 48 49 51 51 52 52 53 54 56 56 56 58 58 60 60 61 62 63 63 2005, Hong Minh Sn

CNG NGH I TNG TRONG IU KHIN PHN TN 5.1 Lp trnh hng i tng 5.2 Phn tch v thit k hng i tng 5.2.1 Ngn ng m hnh ha thng nht UML 5.2.2 Mu thit k 5.2.3 Phn mm khung 5.3 Phn mm thnh phn 5.4 i tng phn tn KIN TRC I TNG PHN TN 6.1 Yu cu chung 6.2 Cc mu thit k 6.3 Gii thiu chun CORBA 6.4 Gii thiu chun COM/DCOM 6.4.1 Giao din 6.4.2 i tng COM 6.4.3 Giao tip gia client v object 6.4.4 Ngn ng m t giao din 6.4.5 M hnh i tng thnh phn phn tn DCOM CC M HNH NG DNG IU KHIN PHN TN 7.1 IEC-61131 7.1.1 M hnh phn mm 7.1.2 M hnh giao tip 7.2 IEC-61499 7.2.1 M hnh h thng 7.2.2 M hnh thit b 7.2.3 M hnh ti nguyn 7.2.4 M hnh ng dng 7.2.5 M hnh khi chc nng 7.2.6 M hnh phn tn 7.2.7 M hnh qun l 7.2.8 M hnh trng thi hot ng MT S CHUN GIAO TIP CNG NGHIP 8.1 MMS 8.2 IEC-61131-5 8.2.1 M hnh giao tip mng 8.2.2 Dch v giao tip 8.2.3 Cc khi chc nng giao tip 8.3 OPC 8.3.1 Tng quan v kin trc OPC

6

7

8

8.3.2 OPC Custom Interfaces 8.3.3 OPC Automation Interface 8.4 Ngn ng nh du kh m XML 8.4.1 Gii thiu chung 8.4.2 ng dng XML trong phn mm khung iPC 9 M T H THNG IU KHIN PHN TN 9.1 Cc phng php m t ha 9.2 Lu P&ID 9.2.1 Chun ISA S5.1 9.2.2 Chun ISA S5.3 9.3 M hnh ha hng i tng

3 65 66 67 67 68 70 70 71 71 75 77 78 78 79 81 83 84 85 85 87 87 88 89 91 92 92 92 92 93 94 94 94 95 95 95 95 97 97 97 97 97

10 LP TRNH IU KHIN PHN TN 10.1 Lp trnh theo chun IEC 61131-3 10.1.1 Kiu d liu 10.1.2 T chc chng trnh 10.1.3 Ngn ng FBD 10.1.4 Ngn ng ST 10.1.5 Ngn ng SFC 10.2 Lp trnh vi ngn ng bc cao 11 CHC NNG IU KHIN GIM ST 11.1 Gii thiu chung v cc h iu khin gim st 11.1.1 Cc thnh phn chc nng c bn 11.1.2 Cng c phn mm SCADA/HMI 11.2 Xy dng cu trc h thng 11.3 Thit k giao din ngi-my 11.3.1 Yu cu chung 11.3.2 Cc phng php giao tip ngi-my 11.3.3 Thit k cu trc mn hnh 11.3.4 Cc nguyn tc thit k 12 TNH SN SNG V TIN CY CA CC H KPT 12.1 t vn 12.2 C ch d phng 12.3 C ch an ton 12.4 C ch khi ng li sau s c 12.5 Bo mt 12.6 Bo tr 13 NH GI V LA CHN GII PHP IU KHIN PHN TN 13.1 nh gi v la chn cc sn phm DCS tch hp trn vn 13.1.1 Phm vi chc nng 13.1.2 Cu trc h thng v cc thit b thnh phn 13.1.3 Tnh nng m

2005, Hong Minh Sn

13.1.4 13.1.5 13.1.6 13.2 So

Pht trin h thng tin cy v tnh sn sng Gi thnh, chi ph snh gii php DCS tch hp trn vn vi cc gii php khc

4 97 98 98 98 100 100 100 100 100 100

14 GII THIU MT S H IU KHIN PHN TN TIU BIU 14.1 PCS7 ca Siemens 14.2 PlantScape ca Honeywell 14.3 DeltaV ca Fisher Rosermount 14.4 Centum CS1000/CS3000 ca Yokogawa 14.5 AdvantOCS ca ABB

15 MT S HNG NGHIN CU V NG DNG 101 15.1 Tr tu nhn to phn tn 101 15.2 iu khin v gim st cc h thng giao thng 102 15.2.1 t vn 102 15.2.2 M hnh h thng iu khin n tn hiu giao thng bng cng ngh Agent 102 15.3 iu khin v gim st cc h thng sn xut v cung cp in 104 TI LIU THAM KHO 105

2005, Hong Minh Sn

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1

NHP MN

1.1 Phm vi cpPhm vi cp ca mn H thng iu khin phn tn l cc h thng t ng ho hin i c cu trc phn tn trong cng nghip cng nh trong nhiu lnh vc khc. Mn hc c xy dng trn c s ng dng cc tin b mi nht ca k thut iu khin, k thut truyn thng cng nghip, cng ngh phn mm vo trong cc h thng iu khin v gim st. Mc ch ca mn hc cho sinh vin lm quen vi cu trc v cc thit b phn cng cng nh cc thnh phn phn mm ca cc h thng iu khin v gim st hin i, nm c cc nguyn tc v phng php c bn cho hng gii quyt nhng bi ton thng c t ra trong thc t nh thit k cu trc h thng, tch hp h thng, a vo vn hnh v chn on h thng. Bn cnh , mn hc a ra cc hng nghin cu l thuyt v ng dng mi, to c s cho cc sinh vin mun tip tc hc v nghin cu cc bc sau i hc.

1.2 Ni dung chng trnhNi dung bi ging bao gm cc ch chnh sau: Cu trc cc h thng iu khin v gim st: M hnh phn cp, cc thnh phn chc nng c bn, m t h thng C s tin hc: X l phn tn, cng ngh hng i tng, phn mm thnh phn Cc h thng iu khin phn tn truyn thng (DCS): Cu trc h thng, cc thnh phn h thng, phng php pht trin h thng, gii thiu mt s h DCS tiu biu. Cc h thng iu khin phn tn trn nn PLC (PLC-based DCS) Cc h thng iu khin phn tn trn nn PC (PC-based DCS) H thng iu khin gim st v thu thp d liu (SCADA): Cu trc h thng, cng c phn mm, thit k giao din ngi-my Cc chun giao tip cng nghip: MMS, OPC, XML Cc hng nghin cu v ng dng.

1.3 Yu cu kin thc c sPhn ln ni dung cc bi ging mang tnh cht tng hp, lin mn, ginh cho sinh vin nm cui. Bn cnh cc mn c s chuyn ngnh, yu cu hc vin phi nm vng kin thc c bn trong cc mn hc sau: iu khin s Mng truyn thng cng nghip K thut lp trnh C++ (hng i tng)

2005, Hong Minh Sn

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1.4 Tng quan cc gii php iu khin1.4.1 c trng cc lnh vc ng dng iu khin

Khi xy dng mt gii php iu khin, ta phi quan tm ti qui m v c th ca lnh vc ng dng. Mt vi lnh vc ng dng tiu biu v cc gii php iu khin c th tng ng c tm tt di y. iu khin cc thit b v my mc n l (cng nghip v gia dng): Cc my mc, thit b c sn xut hng lot, v vy yu cu u t cho gii php iu khin phi tht tit kim (chng trnh nh, tn t b nh). Cc bi ton iu khin c th rt khc nhau, t iu khin logic ti iu khin phn hi, iu khin chuyn ng, iu khin m, Cc gii php iu khin tiu biu l iu khin nhng (P, C), CNC, PLC,... T ng ha cng nghip, c chia ra hai lnh vc: Cng nghip ch bin, khai thc: Cc bi ton iu khin tiu biu l iu khin qu trnh (process control), iu khin trnh t (sequence control), bn cnh iu khin logic. Cc thit b c dng ph bin l PLC, DCS, (I)PC, Compact Digital Controllers. Cng nghip ch to, lp rp: Cc bi ton iu khin tiu biu l iu khin logic, iu khin chuyn ng, iu khin s kin ri rc. Cc thit b c dng ch yu l PLC, CNC, PC. Nay cc h DCS cng tm c mt s ng dng trong lnh vc ny. iu khin cc h thng giao thng, vn ti: c th l cc bi ton iu khin logic, iu khin s kin ri rc. Cc thit b c dng l PLC, DCS, PC, P, C,... iu khin cc h thng phn phi nng lng (du kh, gas, in): Kt hp gia cc bi ton iu khin qu trnh vi iu khin s kin ri rc, iu khin logic, s dng PLC, DCS, IPC,... T ng ha ta nh: Rle, PLC, p, C,... iu khin v gim st cc h thng quc phng: IPC, P, C, DSP v cc thit b c chng khc. iu khin v gim st cc h thng thy li, mi trng: PLC, IPC, ... ...

1.4.2

Cc h thng iu khin cng nghip

Chng trnh hc t trng tm vo cc gii php iu khin cng nghip, chia lm hai lnh vc ng dng c bn: Cng nghip ch bin, khai thc (Process Industry): Du kh, ha du, ha m phm, dc phm, xi mng, giy, ... Cng nghip ch to, lp rp (Manufactoring Industry): Cng nghip t, my cng c, cng nghip in t, vi in t, thit b dn dng,...

2005, Hong Minh Sn

7T NG HA QU TRNH (Cng nghip ch bin, khai thc) Cc b iu chnh c T NG HA X NGHIP (Cng nghip ch to, lp rp) Cc thit b c kh Rle in c, (1920) Cc mch logic lp trnh cng (PLD, 1960)

Thit b iu chnh PID kh nn (1920-1930) Thit b iu chnh PID in t (1940-1950) iu khin s trc tip (DDC, 1965-1975)

Thit b iu khin kh trnh (PLC, 1970)

B iu chnh s gn (CDC, 1980)

H KPT tch hp (DCS, 1975) PLC-based DCS PLC mm (Soft-PLC, 1996)

PC cng nghip (IPC) PC-104, CompactPCI, SBC (PC-based Control) PC-based DCS

H iu khin lai H iu khin trng (FCS, 2000)

Hnh 1-1:

Lch s pht trin cc gii php iu khin

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2

CU TRC CC H THNG IU KHIN V GIM ST

2.1 Cu trc v cc thnh phn c bnCc thnh phn c bn ca mt h thng iu khin v gim st qu trnh c minh ha trn Hnh 2-1. Cc cm bin v c cu chp hnh ng vai tr l giao din gia cc thit b iu khin vi qu trnh k thut. Trong khi , h thng iu khin gim st ng vai tr giao din gia ngi vn hnh v my. Cc thit b c th c ghp ni trc tip im-im, hoc thng qua mng truyn thng.

H thng iu khin gim st NI

Thit b iu khin t ng NI NI I/O

NI NI ni trc tip ni qua mng

I/O

NI Cm bin v chp hnh NI I/O

network interface (giao din mng) input/output (vo/ra)

Qu trnh k thut Hnh 2-1: Cc thnh phn c bn ca mt h thng iu khin v gim st

Ty theo loi cm bin, tn hiu ca chng a ra c th l tn hiu nh phn, tn hiu s hay tn hiu tng t theo cc chun in hc thng dng khc nhau (1..10V, 0..5V, 4..20mA, 0..20mA, v.v...). Trc khi c th x l trong my tnh s, cc tn hiu o cn c chuyn i, thch ng vi chun giao din vo/ra ca my tnh. Bn cnh , ta cng cn cc bin php cch ly in hc trnh s nh hng xu ln nhau gia cc thit b. chnh l cc chc nng ca cc module vo/ra (I/O). Tm li, mt h thng iu khin v gim st bao gm cc thnh phn chc nng chnh sau y: Giao din qu trnh: Cc cm bin v c cu chp hnh, ghp ni vo/ra, chuyn i tn hiu. 2005, Hong Minh Sn

9 Thit b iu khin t ng: Cc thit b iu khin nh cc b iu khin chuyn dng, b iu khin kh trnh PLC (programmable logic controller), thit b iu chnh s n l (compact digital controller) v my tnh c nhn cng vi cc phn mm iu khin tng ng. H thng iu khin gim st: Cc thit b v phn mm giao din ngi my, cc trm k thut, cc trm vn hnh, gim st v iu khin cao cp. H thng truyn thng: Ghp ni im-im, bus cm bin/chp hnh, bus trng, bus h thng. H thng bo v, c ch thc hin chc nng an ton.

2.2 M hnh phn cpCng nhng cp di th cc chc nng cng mang tnh cht c bn hn v i hi yu cu cao hn v nhanh nhy, thi gian phn ng. Mt chc nng cp trn c thc hin da trn cc chc nng cp di, tuy khng i hi thi gian phn ng nhanh nh cp di, nhng ngc li lng thng tin cn trao i v x l li ln hn nhiu. Thng thng, ngi ta ch coi ba cp di thuc phm vi ca mt h thng iu khin v gim st. Tuy nhin, biu th hai cp trn cng (qun l cng ty v iu hnh sn xut) trn gip ta hiu thm mt m hnh l tng cho cu trc chc nng tng th cho cc cng ty sn xut cng nghip.Tnh ton gi thnh, li sut thng k s liu sn xut, kinh doanh, x l n t hng, k hoch ti nguyn nh gi kt qu, lp k hoch sn xut, bo dng my mc, tnh ton ti u ho sn xut Gim st, vn hnh, iu khin cao cp, Lp bo co iu khin, iu chnh, bo v, an ton ghi chp tng trnh o lng, truyn ng, chuyn i tn hiu

QL cng ty iu hnh sn xut

iu khin gim st Cp iu khin qu trnh iu khin

Chp hnh

Cp trng

Qu trnh k thut Hnh 2-2: M hnh phn cp chc nng ca mt h thng iu khin v gim st

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2.2.1

Cp chp hnh

Cc chc nng chnh ca cp chp hnh l o lng, truyn ng v chuyn i tn hiu trong trng hp cn thit. Thc t, a s cc thit b cm bin (sensor) hay c cu chp hnh (actuator) cng c phn iu khin ring cho vic thc hin o lng/truyn ng c chnh xc v nhanh nhy. Cc thit b thng minh1 cng c th m nhn vic x l th thng tin, trc khi a ln cp iu khin.

2.2.2

Cp iu khin

Nhim v chnh ca cp iu khin l nhn thng tin t cc cm bin, x l cc thng tin theo mt thut ton nht nh v truyn t li kt qu xung cc c cu chp hnh. Khi cn iu khin th cng, nhim v c ngi ng my trc tip m nhim qua vic theo di cc cng c o lng, s dng kin thc v kinh nghim thc hin nhng thao tc cn thit nh n nt ng/m van, iu chnh cn gt, nm xoay v.v... Trong mt h thng iu khin t ng hin i, vic thc hin th cng nhng nhim v c thay th bng my tnh.

2.2.3

Cp iu khin gim st

Cp iu khin gim st c chc nng gim st v vn hnh mt qu trnh k thut. Khi a s cc chc nng nh o lng, iu khin, iu chnh, bo ton h thng c cc cp c s thc hin, th nhim v ca cp iu khin gim st l h tr ngi s dng trong vic ci t ng dng, thao tc, theo di, gim st vn hnh v x l nhng tnh hung bt thng. Ngoi ra, trong mt s trng hp, cp ny cn thc hin cc bi ton iu khin cao cp nh iu khin phi hp, iu khin trnh t v iu khin theo cng thc (v d trong ch bin dc phm, ho cht). Khc vi cc cp di, vic thc hin cc chc nng cp iu khin gim st thng khng i hi phng tin, thit b phn cng c bit ngoi cc my tnh thng thng (my tnh c nhn, my trm, my ch, termimal,...). Nh ta s thy, phn cp chc nng nh trn s tin li cho vic thit k h thng v la chn thit b. Trong thc t ng dng, s phn cp chc nng c th khc mt cht so vi trnh by y, ty thuc vo mc t ng ho v cu trc h thng c th. Trong nhng trng hp ng dng n gin nh iu khin trang thit b dn dng (my git, my lnh, iu ha m,...), s phn chia nhiu cp c th hon ton khng cn thit. Ngc li, trong t ng ha mt nh my ln hin i nh in nguyn t, sn xut xi mng, lc du, ta c th chia nh hn na cc cp chc nng tin theo di.

1

Mt thit b c gi l thng minh, khi n c kh nng x l thng tin. Thc t, mi thit b thng minh phi c t nht mt b vi x l ring.

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2.3 Cu trc iu khinBin th ca cu trc c bn trn Hnh 2-1 tm thy trong cc gii php thc t khc nhau s phn b chc nng iu khin cng nh s phn b v tr cc my tnh qu trnh v ph kin c la chn. Cn c vo , ta c th phn bit gia cu trc iu khin tp trung v cu trc iu khin phn tn, cu trc vo/ra tp trung v cu trc vo/ra phn tn.

2.3.1

iu khin tp trung

Cu trc tiu biu ca mt h iu khin tp trung (centralized control system) c minh ha trn Hnh 2-3. Mt my tnh duy nht c dng iu khin ton b qu trnh k thut. My tnh iu khin y (MTK) c th l cc b iu khin s trc tip (DDC), my tnh ln, my tnh c nhn hoc cc thit b iu khin kh trnh. Trong iu khin cng nghip, my tnh iu khin tp trung thng thng c t ti phng iu khin trung tm, cch xa hin trng. Cc thit b cm bin v c cu chp hnh c ni trc tip, im-im vi my tnh iu khin trung tm qua cc cng vo/ra ca n. Cch b tr vo/ra ti my tnh iu khin nh vy cng c gi l vo/ra tp trung (central I/O).Phng iu khin trung tm MTK I/O

Hin trng

A

S

A

S

A

S

Phn on 1

Phn on 2 I/O: input/output A: actuator

Phn on n S: sensor

Hnh 2-3: Cu trc iu khin tp trung vi vo/ra tp trung

y l cu trc iu khin tiu biu trong nhng nm 1965-1975. Ngy nay, cu trc tp trung trn y thng thch hp cho cc ng dng t ng ha qui m va v nh, iu khin cc loi my mc v thit b bi s n gin, d thc hin v gi thnh mt ln cho my tnh iu khin. im ng ch y l s tp trung ton b tr tu, tc chc nng x l thng tin trong mt thit b iu khin duy nht. Tuy nhin, cu trc ny bc l nhng hn ch sau: Cng vic ni dy phc tp, gi thnh cao Vic m rng h thng gp kh khn tin cy km. 2005, Hong Minh Sn

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2.3.2

iu khin tp trung vi vo/ra phn tn

Cu trc vo/ra tp trung vi cch ghp ni im-im th hin mt nhc im c bn l s lng ln cc cp ni, dn n gi thnh cao cho dy dn v cng thit k, lp t. Mt hn ch khc na l phng php truyn dn tn hiu thng thng gia cc thit b trng v thit b iu khin d chu nh hng ca nhiu, gy ra sai s ln. Vn ny c khc phc bng phng php dng bus trng nh nu trong phn trc. Hnh 2-4 minh ha mt cu hnh mng n gin. y cc module vo/ra c y xung cp trng gn k vi cc cm bin v c cu chp hnh, v vy c gi l cc vo/ra phn tn (Distributed I/O) hoc vo/ra t xa (Remote I/O). Mt cch ghp ni khc l s dng cc cm bin v c cu chp hnh thng minh (mu xm trn hnh v), c kh nng ni mng trc tip khng cn thng qua cc module vo/ra. Bn cnh kh nng x l giao thc truyn thng, cc thit b ny cn m nhim mt s chc nng x l ti ch nh lc nhiu, chnh nh thang o, t t ch , im lm vic, chn on trng thi,v.v... Trong nhiu trng hp, cc thit b c th m nhim c nhim v iu khin n gin.

MTK Phng K trung tm bus trng I/O I/O I/O S Hin trng A S A

S

AHnh 2-4:

S

A

S

A

Cu trc iu khin tp trung vi vo/ra phn tn

S dng bus trng v cu trc vo/ra phn tn mang li cc u im sau: Tit kim dy dn v cng i dy, ni dy Gim kch thc hp iu khin Tng linh hot h thng nh s dng cc thit b c giao din chun v kh nng ghp ni n gin Thit k v bo tr d dng nh cu trc n gin Kh nng chn on tt hn (cc thit b hng c pht hin d dng) Tng tin cy ca ton h thng.

2.3.3

iu khin phn tn

Trong a s cc ng dng c qui m va v ln, phn tn l tnh cht c ha ca h thng. Mt dy chuyn sn xut thng c phn chia thnh nhiu phn on, c th c phn b ti nhiu v tr cch xa nhau. khc 2005, Hong Minh Sn

13 phc s ph thuc vo mt my tnh trung tm trong cu trc tp trung v tng tnh linh hot ca h thng, ta c th iu khin mi phn on bng mt hoc mt s my tnh cc b, nh Hnh 2-5 minh ha.PHNG IU KHIN TRUNG TM

MTGS

MTGS

bus h thng

MTK 1

MTK 2

PHNG IU KHIN CC B

MTK n

A

S

A

S HIN TRNG

A

S

Phn on 1

Phn on 2

Phn on n

Hnh 2-5: Cu trc iu khin phn tn vi vo/ra tp trung

Cc my tnh iu khin cc b thng c t ri rc ti cc phng iu khin/phng in ca tng phn on, phn xng, v tr khng xa vi qu trnh k thut. Cc phn on c lin h tng tc vi nhau, v vy iu khin qu trnh tng hp cn c s iu khin phi hp gia cc my tnh iu khin. Trong phn ln cc trng hp, cc my tnh iu khin c ni mng vi nhau v vi mt hoc nhiu my tnh gim st (MTGS) trung tm qua bus h thng. Gii php ny dn n cc h thng c cu trc iu khin phn tn, hay c gi l cc h iu khin phn tn (HKPT). u th ca cu trc iu khin phn tn khng ch dng li linh hot cao hn so vi cu trc tp trung. Hiu nng cng nh tin cy tng th ca h thng c nng cao nh s phn tn chc nng xung cc cp di. Vic phn tn chc nng x l thng tin v phi hp iu khin c s gim st t cc trm vn hnh trung tm m ra cc kh nng ng dng mi, tch hp trn vn trong h thng nh lp trnh cao cp, iu khin trnh t, iu khin theo cng thc v ghp ni vi cp iu hnh sn xut.

2.3.4

iu khin phn tn vi vo/ra phn tn

Lu rng Hnh 2-5 ch minh ha cch ghp ni im-im gia mt my tnh iu khin vi cc cm bin v c cu chp hnh, s dng vo/ra tp trung. Tuy nhin, ta cng c th s dng bus trng thc hin cu trc vo/ra phn tn nh trn Hnh 2-6. Khi , my tnh iu khin c th t ti 2005, Hong Minh Sn

14 phng iu khin trung tm hoc ti cc phng iu khin cc b, ty theo qui m ca h thng v kh nng ko di ca bus trng. Gii php s dng cc h iu khin phn tn vi cu trc vo/ra phn tn v cc thit b trng thng minh chnh l xu hng trong xy dng cc h thng iu khin v gim st hin i. Bn cnh tin cy cao, tnh nng m v linh hot cao th yu t kinh t cng ng vai tr quan trng. Vic phn tn chc nng x l thng tin, chc nng iu khin theo b rng cng nh theo chiu su l tin cho kin trc tr tu phn tn (distributed intelligence) trong tng lai.

MTGS

MTGS bus h thng

PHNG IU KHIN TRUNG TM

MTK n

MTK 1 bus trng I/O

MTK 2 bus trng I/O PHNG IU KHIN CC B bus trng I/O

S

A

S

A

SHIN TRNG

A

Phn on 1

Phn on 2

Phn on n

Hnh 2-6:

Cu trc iu khin phn tn vi vo/ra phn tn

2005, Hong Minh Sn

15

3

CC THNH PHN CA MT H IU KHIN PHN TN

3.1 Cu hnh c bnCu hnh c bn mt h iu khin phn tn c minh ha trn Hnh 3-1, bao gm cc thnh phn sau: Cc trm iu khin cc b (local control station, LCS), i khi cn c gi l cc khi iu khin cc b (local control unit, LCU) hoc cc trm qu trnh (process station, PS). Cc trm vn hnh (operator station, OS) Trm k thut (engineering station, ES) v cc cng c pht trin H thng truyn thng (field bus, system bus).

My tnh PC phng th Factory LAN

Operator Station

Operator Station

Engineering Station System bus Local Control Station Remote I/O Station

Local Control Station

PROCESSHnh 3-1: Cu hnh c bn mt h iu khin phn tn

y l cu hnh ti thiu, cc cu hnh c th c th cha cc thnh phn khc nh trm vo/ra t xa (remote I/O station), cc b iu khin chuyn dng,...

3.1.1

Trm iu khin cc b

Thng thng, cc trm iu khin cc b c xy dng theo cu trc module. Cc thnh phn chnh bao gm: B cung cp ngun, thng thng c d phng Khi x l trung tm (CPU), c th la chn loi c d phng 2005, Hong Minh Sn

16 Giao din vi bus h thng, thng thng cng c d phng Giao din vi bus trng nu s dng cu trc vo/ra phn tn Cc module vo/ra s cng nh tng t, c bit l cc module vo/ra an ton chy n Trong cu trc vo/ra tp trung, cc module vo/ra c ni vi CPU thng qua bus ni b ng sau gi (backplane-bus). Chnh v vy, cc module ny cng phi do nh sn xut cung cp km theo CPU. Trong cc h thng iu khin qu trnh, mt trm iu khin cc b cng thng c ci t giao din HART v cc module ghp ni ph kin khc. Cc thit b ny c lp t trong t iu khin cng vi cc linh kin h tr khc nh hng kp u dy, cc b chuyn i tn hiu (transducers), cc khi u cui (terminal blocka),... Cc t iu khin thng c t trong phng iu khin/phng in bn cnh phng iu khin trung tm hoc ri rc gn khu vc hin trng. Cc chc nng do trm iu khin cc b m nhim bao gm: iu khin qu trnh (process control): iu khin cc mch vng kn (nhit , p sut, lu lng, pH, m c,...). Hu ht cc mch vng n c iu khin trn c s lut PID, gii quyt bi ton iu khin iu chnh, iu khin t l, iu khin tng. Cc h thng hin i cho php iu khin m, iu khin da m hnh (model-based control), iu khin thch nghi, ... iu khin trnh t (sequential control, sequence control) iu khin logic Thc hin cc cng thc (recipe control). t cc tn hiu u ra v trng thi an ton trong trng hp c s c h thng Lu tr tm thi cc tn hiu qu trnh trong trng hp mt lin lc vi trm vn hnh Nhn bit cc trng hp vt ngng gi tr v to cc thng bo bo ng. Chnh v y l thnh phn quan trng nht trong h thng, i a s cc trm iu khin cc b c tnh nng kim tra v sa li (error checking and correcting, ECC), cng nh cho php la chn cu hnh d phng. Mt iu quan trng l mt trm iu khin cc b phi c kh nng m bo tip tc thc hin cc chc nng ni trn trong trng hp trm vn hnh hoc ng truyn bus h thng c s c. Cc my tnh iu khin c th l my tnh c chng ca nh cung cp (vendor-specific controller), PLC hoc my tnh c nhn cng nghip. Da trn c s ny c th phn loi cc h thng iu khin phn tn c mt hin nay trn th trng thnh cc h cc h truyn thng (sau y gi l DCS truyn thng), cc h trn nn PLC (PLC-based DCS) v cc h trn nn PC (PC-based DCS). 2005, Hong Minh Sn

17 Bt k chng loi thit b no c s dng, cc yu cu quan trng nht v mt k thut c t ra cho mt trm iu khin cc b l: Tnh nng thi thc tin cy v tnh sn sng Lp trnh thun tin, cho php s dng/ci t cc thut ton cao cp Kh nng iu khin lai (lin tc, trnh t v logic).

3.1.2

Bus trng v cc trm vo/ra t xa

Khi s dng cu trc vo/ra phn tn, cc trm iu khin cc b s c b sung cc module giao din bus ni vi cc trm vo/ra t xa (remote I/O station) v mt s thit b trng thng minh. Cc yu cu chung t ra vi bus trng l tnh nng thi gian thc, mc n gin v gi thnh thp. Bn cnh , i vi mi trng d chy n cn cc yu cu k thut c bit khc v chun truyn dn, tnh nng in hc ca cc linh kin mng, cp truyn,... Cc loi bus trng c h tr mnh nht l Profibus-DP, Foundation Fieldbus, DeviceNet v AS-I. Trong mi trng i hi an ton chy n th Profibus-PA v Foundation Fieldbus H1 l hai h c s dng ph bin nht. Mt trm vo/ra t xa thc cht c cu trc khng khc lm so vi mt trm iu khin cc b, duy ch thiu khi x l trung tm cho chc nng iu khin. Thng thng, cc trm vo/ra t xa c t rt gn vi qu trnh k thut, v th tit kim nhiu cp truyn v n gin ha cu trc h thng. Trm vo/ra t xa cng c th t cng v tr vi trm iu khin cc b, tuy nhin nh vy khng li dng c u im ca cu trc ny. Khc vi cu trc vo/ra tp trung, cu trc vo/ra phn tn cho php s dng cc trm vo/ra t xa ca cc nh cung cp khc vi iu kin c h tr loi bus trng qui nh. Tuy nhin, c th khai thc ti a kh nng cc cng c phn mm tch hp v m bo tng thch hon ton gia cc thnh phn trong mt h DCS, vic dng trn sn phm ca mt hng vn l gii php an ton nht. Bn cnh phng php ghp ni thit b iu khin vi qu trnh k thut thng qua cc module vo/ra, ta c th s dng cc cm bin hoc c cu chp hnh c giao din bus trng. Qua c th n gin ha cu trc h thng hn na, tit kim tit kim ch trong t iu khin v nng cao tnh nng thi gian thc ca h thng do tn dng c kh nng x l thng tin ca cc thit b trng. Trn Hnh 3-4 l hnh nh mt s t iu khin DCS. Hnh bn tri l mt trm PCS7 (Siemens) vi b iu khin lp t cng cc module vo/ra phn tn. Hnh gia minh ha mt trm vo/ra t xa lp c lp. T iu khin bn phi minh ha trm iu khin cc b DeltaV (Fisher-Rosermount) s dng gii php Foundation Fieldbus (khng cn cc module cc vo/ra). 2005, Hong Minh Sn

18

Hnh 3-2:

M s hnh nh t iu khin DCS

3.1.3

Trm vn hnh

Trm vn hnh v trm k thut c t ti phng iu khin trung tm. Cc trm vn hnh c th hot ng song song, c lp vi nhau. tin cho vic vn hnh h thng, ngi ta thng sp xp mi trm vn hnh tng ng vi mt phn on hoc mt phn xng. Tuy nhin, cc phn mm chy trn tt c cc trm hon ton ging nhau, v th trong trng hp cn thit mi trm u c th thay th chc nng ca cc trm khc. Cc chc nng tiu biu ca mt trm vn hnh gm c: Hin th cc hnh nh chun (hnh nh tng quan, hnh nh nhm, hnh nh tng mch vng, hnh nh iu khin trnh t, cc th thi gian thc v th qu kh) Hin th cc hnh nh ha t do (lu cng ngh, cc phm iu khin) H tr vn hnh h thng qua cc cng c thao tc tiu biu, cc h thng hng dn ch o v hng dn tr gip To v qun l cc cng thc iu khin (cho iu khin m) X l cc s kin, s c X l, lu tr v qun l d liu Chn on h thng, h tr ngi vn hnh v bo tr h thng H tr lp bo co t ng Khc vi cc trm iu khin, hu ht cc h DCS hin i u s dng cc sn phm thng mi thng dng nh my tnh c nhn (cng nghip) chy trn nn WindowsNT/2000, hoc cc my tnh trm chy trn nn UNIX. Cng vi cc mn hnh mu ln (thng l 19inch) vi phn gii cao theo di qu trnh sn xut, mt trm vn hnh hin i bao gi cng c cc 2005, Hong Minh Sn

19 thit b thao tc chun nh bn phm v chut. Mt trm vn hnh c th b tr theo kiu mt ngi s dng (mt hoc nhiu mn hnh), hoc nhiu ngi s dng vi vi nhiu Terminals (Hnh 3-3). Cc phn mm trn trm vn hnh bao gi cng i km ng b vi h thng, song thng h tr cc chun phn mm v chun giao tip cng nghip nh TCP/IP, DDE (Dynamic Data Exchange), OLE (Object Linking and Embedding), ODBC (Open Data Base Connection), OPC (OLE for Process Control).Operator Terminals Engineering Station Operator Station Terminals bus

System bus

Controller

Hnh 3-3:

Cc phng php b tr trm vn hnh

c im tiu biu ca cc trm vn hnh hin i l s dng k thut giao din ngi-my kiu a ca s vi cc phn t giao din chun. Tuy nhin, vic thit k cc mn hnh giao din cng nghip khc vi cc giao din ng dng vn phng, i hi kin thc tng hp v qu trnh cng ngh, m thut cng nghip, tm l hc cng nghip v cng ngh phn mm. Vn ny s c cp chi tit sau.

3.1.4

Trm k thut v cc cng c pht trin

Trm k thut l ni ci t cc cng c pht trin, cho php t cu hnh cho h thng, to v theo di cc chng trnh ng dng iu khin v giao din ngi my, t cu hnh v tham s ha cc thit b trng. Vic to ng dng iu khin hu ht c thc hin theo phng php khai bo, t tham s v ghp ni cc khi chc nng c sn trong th vin. Cng nh cc trm vn hnh, thit b s dng thng thng l cc my tnh c nhn (cng nghip) chy trn nn Windows95/98/NT/2000 hoc UNIX. Mt s c tnh tiu biu ca cc cng c pht trin trn trm k thut l: Cc cng c pht trin c tch hp sn trong h thng Cng vic pht trin (Engineering) khng yu cu c phn cng DCS ti ch 2005, Hong Minh Sn

20 Cc ngn ng lp trnh thng dng l s khi hm (FBD-Function Block Diagram, hoc CFC-Continuous Function Chart) v biu tin trnh (SFC-Sequential Function Chart), tng t IEC61131-3 FBD () v SFC Mt d n c th do nhiu ngi cng phi hp pht trin song song Giao din vi cc h thng cp trn (CAD/CAM, MES, PPS, ERP,...) vic pht trin h thng phn mm c thun li, cc nh sn xut cung cp cc th vin khi hm chuyn dng. Bn cnh , nhiu nh sn xut cng cung cp phn mm m phng ngi pht trin h thng c th to cc u vo/ra m phng, gip cho vic pht trin phn mm c chc chn, an ton hn. Trong mt s h thng, ngi ta khng phn bit gia trm vn hnh v trm k thut, m s dng mt bn phm c kha chuyn qua li gia hai ch vn hnh v pht trin.

3.1.5

Bus h thng

Bus h thng c chc nng ni mng cc trm iu khin cc b vi nhau v vi cc trm vn hnh v trm k thut. Trong a s cc h thng ng dng, ngi ta la chn cu hnh c d phng cho bus h thng. Thm na, ci thin tnh nng thi gian thc, nhiu khi mt mng ring bit (c th c c d phng) c s dng ghp ni cc trm iu khin cc b (bus iu khin, control bus). Gii php mng c th c chng ca ring cng ty, hoc da trn mt mng chun quc t. Cc h thng mng c s dng nhiu nht l Ethernet, Profibus-FMS v ControlNet. c im ca vic trao i thng tin qua bus h thng l lu lng thng tin ln, v vy tc ng truyn phi tng i cao. Tnh nng thi gian thc cng l mt yu cu c t ra (nht l i vi bus iu khin), tuy nhin khng nghim ngt nh vi bus trng. Thi gian phn ng thng ch yu cu nm trong phm vi 0,1s tr ln. S lng trm tham gia thng khng ln v nhu cu trao i d liu khng c t bin ln. V vy i vi mng Ethernet, tnh bt nh ca phng php truy nhp bus CSMA/CD thng khng phi l vn gy lo ngh. Hnh 3-4 minh ha cu hnh tiu biu ca mt h iu khin phn tn hin i. Bn cnh cc thnh phn m t, mt cu hnh tiu biu thng c thm mt s trm server, my tnh phn tch, my in, mt s b iu khin cc b chuyn dng,...

2005, Hong Minh Sn

21LAB Factory Server

OS

OS

ES

SS

SYSTEM BUS Control Station 1 FIELDBUS I/O Controller Motor Control Center Control Station 2 Control Station n

S

AI/O

S

A

S A

Controller

SI/O

A

S

AI/O

Controller

S

A

S

A

S

A

Phn on 1

Phn on 2

Phn on n

Hnh 3-4:

Cu hnh tiu biu mt h iu khin phn tn hin i

3.2 Phn loi cc h DCS3.2.1 Cc h DCS truyn thng

Cc h ny s dng cc b iu khin qu trnh c chng theo kin trc ring ca nh sn xut. Cc h c thng ng kn, t tun theo cc chun giao tip cng nghip, cc b iu khin c s dng cng thng ch lm nhim v iu khin qu trnh, v vy phi s dng kt hp PLC cho cc bi ton iu khin logic v iu khin trnh t. Cc h mi c tnh nng m tt hn, mt s b iu khin lai m nhim c cc chc nng iu khin qu trnh, iu khin trnh t v iu khin logic (hybrid controller). 2005, Hong Minh Sn

22 h tr cc bi ton iu khin qu trnh din ra ng thi, khi x l trung tm c ci t mt h iu hnh thi gian thc, a nhim - hoc ca ring nh sn xut pht trin hoc mt sn phm thng dng nh pSOS, TSOS, VRTX,... Chu k thi gian nh nht thc hin cc mch vng iu khin thng nm trong khong 10-100ms, trong trng hp c bit (v d cho nh my in) c th ti 1ms. Mt s sn phm tiu biu cng vi tn trm iu khin cc b c lit k di y: AdvantOCS (ABB): Advant Controller, h iu hnh ring Freelance 2000 (ABB): D-PS hc D-FC, h iu hnh pSOS Symphonie (ABB): Melody, h iu hnh pSOS DeltaV (Fisher-Rosermount): Visual Controller, h iu hnh TSOS I/A Series (Foxboro): CP60, h iu hnh VRTX PlantScape (Honeywell): PlantScape Controller, h iu hnh ring Centum CS1000/CS3000 (Yokogawa): PFCx-E, AFS10x/AFS20x, h iu hnh ORKID

3.2.2

Cc h DCS trn nn PLC

Thit b iu khin kh trnh (PLC, programmable logic controller) l mt loi my tnh iu khin chuyn dng, do nh pht minh ngi M Richard Morley ln u tin a ra tng vo nm 1968. Da trn yu cu k thut ca General Motors l xy dng mt thit b c kh nng lp trnh mm do thay th cho mch iu khin logic cng, hai cng ty c lp l Allen Bradley v Bedford Associates (sau ny l Modicon) a ra trnh by cc sn phm u tin. Cc thit b ny ch x l c mt tp lnh logic c bn, 128 im vo/ra (1 bit) v 1kByte b nh. Lc u, ci tn programmable controller, vit tt l PC, c s dng rng ri. Trong khi , programmable logic controller hay PLC l thng hiu ng k ca cng ty Allen Bradley. Sau ny, khi my tnh c nhn tr nn ph bin th t vit tt PLC hay c dng hn trnh nhm ln. V vy t y v sau ta s dng khi nim thit b iu khin kh trnh nhng vi t vit tt l PLC. Vi cu trc ghp ni vo/ra linh hot, nguyn tc lm vic n gin theo chu k, kh nng lp trnh v lu tr chng trnh trong b nh khng cn can thip trc tip ti phn cng, PLC nhanh chng thu ht s ch trong gii chuyn ngnh. Vo thi im cc my tnh iu khin chuyn dng v khng chuyn dng u c kch c rt ln v gi thnh rt cao, th vic s dng PLC l gii php l tng thay th cc mch logic t hp v tun t trong iu khin cc qu trnh gin on. Cho n nay, danh mc cc chng loi PLC c mt trn th trng tht phong ph n mc kh c th bao qut. Chng khng nhng khc nhau cng sut lm vic ca b x l trung tm, dung lng b nh v s lng cc cng vo/ra, m cn cc c tnh chc nng nh cu trc linh hot, 2005, Hong Minh Sn

23 phng php lp trnh v kh nng ni mng. Tr mt s loi nh dng trong cc ng dng n gin, hu ht cc PLC hin i u khng dng li vic thc hin cc php tnh logic n gin, m cn c kh nng lm vic vi cc tn hiu tng t v thc hin cc php ton s hc, thm ch c cc thut ton iu khin phn hi nh iu khin nhiu im, PID v iu khin m. Cc b m, b nh thi v mt s hm ton hc thng dng thuc phm vi chc nng chun ca mt PLC. Vic s dng PLC v vy khng ch dng li cc qu trnh gin on, m nay rt ph bin i vi iu khin cc qu trnh lin tc nh trong cng nghip ch bin, khai thc, cng ngh mi trng v.v... Mt s h DCS trn nn PLC tiu biu l SattLine (ABB), Process Logix (Rockwell), Modicon TSX (Schneider Electric), PCS7 (Siemens), Thc cht, ngy nay a s cc PLC va c th s dng cho bi ton iu khin logic v iu khin qu trnh. Tuy nhin, cc PLC c s dng trong cc h iu khin phn tn thng c cu hnh mnh, h tr iu khin trnh t cng vi cc phng php lp trnh hin i (v d SFC). Cu trc phn cng Hnh 3-5 minh ha cc thnh phn chc nng chnh ca mt h thng thit b iu khin kh trnh v quan h tng tc gia chng. V c bn, mt PLC cng c cc thnh phn ging nh mt my vi tnh thng thng, l vi x l, cc b nh lm vic v b nh chng trnh, giao din vo/ra v cung cp ngun. Tuy nhin, mt im khc c bn l cc thnh phn giao din ngi-my nh mn hnh, bn phm v chut khng c trang b y. Vic lp trnh v vy phi c thc hin gin tip bng mt my tnh ring bit, ghp ni vi CPU thng qua giao din thit b lp trnh (thng l mt cng ni tip theo chun RS-232 hoc RS-485). B x l trung tm (Central Processing Unit, CPU) bao gm mt hoc nhiu vi x l, b nh chng trnh, b nh lm vic, ng h nhp v giao din vi thit b lp trnh, c lin kt vi nhau thng qua mt h bus ni b. Nhim v chnh ca CPU l qun l cc cng vo/ra, x l thng tin, thc hin cc thut ton iu khin. B nh chng trnh thng c dng EPROM (Erasable and Programmable Read Only Memory) hoc EEPROM (Electrically Erasable and Programmable Read Only Memory), cha h iu hnh v m chng trnh ng dng. D liu vo/ra cng nh cc d liu tnh ton khc c lu trong b nh lm vic RAM (Random Access Memory). ng h nhp c vai tr to ngt cng iu khin chng trnh theo chu k, thng thng trong khong t 0,01giy ti 1000 pht. Cc thnh phn vo/ra (input/ouput, I/O) ng vai tr l giao din gia CPU v qu trnh k thut. Nhim v ca chng l chuyn i, thch ng tn hiu v cch ly galvanic gia cc thit b ngoi vi (cm bin, c cu chp hnh) v CPU. Cc thnh phn vo/ra c lin kt vi CPU thng qua mt h bus ni b hoc qua mt h bus trng (xem chng 3). 2005, Hong Minh Sn

24 B cung cp ngun (power supply, PS) c vai tr bin i v n nh ngun nui (thng thng 5V) cho CPU v cc thnh phn chc nng khc t mt ngun xoay chiu (110V, 220V,...) hoc mt chiu (12V, 24V,...). Bn cnh cc thnh phn chnh nu trn, mt h thng PLC c th c cc thnh phn chc nng khc nh ghp ni m rng, iu khin chuyn dng v x l truyn thng.CPU Vi x l Vo tng t v vp s (AI, DI) ng h nhp Giao din lp trnh

Ra tng t v ra s (AO, DO)

B nh chng trnh

B nh lm vic

Ngun nui (PS)

Hnh 3-5:

Cc thnh phn chc nng chnh ca mt PLC

Thit k module v thit k gn Ty theo s phn chia chc nng trn cc thnh phn thit b, ta c th phn bit gia cc PLC c thit k module v cc PLC c thit k gn. Trong mt PLC c thit k gn, tt c cc chc nng c tch hp gn trong mt thit b. Thng thng, loi PLC ny c sn mt s cng vo/ra c nh. Mt s cng c tch hp giao din truyn thng cho mt loi bus trng. Tuy nhin, mt s t loi c cu trc gn vn cho php tng s lng cng vo/ra hoc b sung giao din mng bng cc module m rng c bit. PLC c cu trc gn thch hp vi cc bi ton n gin. i vi cc ng dng c qui m va v ln, ta cn s dng cc PLC c thit k module bi linh hot cao. y, hu ht mi thnh phn chc nng c thc hin bi mt module phn cng ring bit, c lp t trn mt hoc nhiu gi . Bn cnh cc thnh phn c bn l CPU, ngun v cc module vo/ra, mt PLC cn c th cha cc module chc nng, cc module ghp ni v module truyn thng. H bus ni b c s dng ghp ni cc module m rng vi CPU thng c gi l bus mt sau (backplane bus). Cc module chc nng (function module, FM) c s dng thc hin mt s nhim v iu khin ring, v d module iu khin PID, module iu khin ng c bc, module cn,... Cc module ny hot ng tng i c lp vi CPU, tuy nhin c th trao i d liu qu trnh v d liu tham s thng qua bus ni b v cc hm hoc khi hm giao tip h thng. 2005, Hong Minh Sn

Tn hiu iu khin

Tn hiu o

25 Cc module ghp ni (interface module, IM) c s dng trong vic m rng h thng khi s lng cc module ln, khng ch trn mt gi . Thng thng, mi gi cn c mt module ngun ring bn cnh module ghp ni. Thng qua cc module ghp ni, mt CPU c th qun l tt c cc module trn cc gi . S lng v chng loi cc module cho php trn mt gi cng nh s lng tng cng ph thuc vo kh nng qun l ca loi CPU c th. Cc module truyn thng (communication module, CM) c vai tr l giao din mng, c s dng ghp ni nhiu PLC vi nhau, vi cc thit b trng v vi my tnh gim st. Cc module truyn thng m nhim x l giao thc mt cch c lp vi CPU. Tuy nhin trong mt s trng hp, b x l trung tm cng c tch hp sn giao din mng cho mt h bus trng thng dng.

3.2.3

Cc h DCS trn nn PC

Gii php s dng my tnh c nhn (PC) trc tip lm thit b iu khin khng nhng c bn ti rng ri, m tr thnh thc t ph bin trong nhng nm gn y. Nu so snh vi cc b iu khin kh trnh (PLC) v cc b iu khin DCS c chng th th mnh ca PC khng nhng nm tnh nng m, kh nng lp trnh t do, hiu nng tnh ton cao v a chc nng, m cn kha cnh kinh t. Cc bc tin ln trong k thut my tnh, cng nghip phn mm v cng ngh bus trng chnh l cc yu t thc y kh nng cnh tranh ca PC trong iu khin cng nghip. DCS trn nn PC l mt hng gii php tng i mi, mi c mt s sn phm trn th trng nh PCS7 (Siemens, gii php Slot-PLC), 4Control (Softing), Stardom (Yokogawa), Ovation (Westinghouse-Emerson Process Management) Hng gii php ny th hin nhiu u im v mt gi thnh, hiu nng tnh ton v tnh nng m. Mt trm iu khin cc b chnh l mt my tnh c nhn cng nghip c ci t mt h iu hnh thi gian thc v cc card giao din bus trng v card giao din bus h thng. Trong gii php iu khin dng my tnh c nhn th mt vn thng rt c quan tm l tin cy ca my tnh. Mt phn ta c th yn tm bi vi cu trc vo/ra phn tn, my tnh iu khin c t trong phng iu khin trung tm vi iu kin mi trng lm vic tt. Mt khc, trn th trng cng c rt nhiu loi my tnh c nhn cng nghip, m bo tin cy cao khng km mt PLC. Mt khi my tnh ch c ci t h iu hnh v phn mm iu khin th kh nng gy li do phn mm cng s c gim thiu. Tuy nhin, i vi cc ng dng c yu cu cao v tnh sn sng, tin cy ca h thng, ta cn c mt gii php d phng thch hp. Gii php n gin v tit kim nht l d phng lnh, c ngha l trong trng hp c s c ti 2005, Hong Minh Sn

26 my tnh iu khin xy ra ta ch cn thay th mt my mi vi cu hnh v cc phn mm c ci t ging ht my chnh. Song gii php tt hn l s dng mt cu hnh d phng nng.

3.3 Cc vn k thutCc vn k thut di y ng vai tr c bit quan trng khi nghin cu v cc h iu khin phn tn, s c cp chi tit trong cc phn sau. Kin trc x l phn tn (distributed processing): Cu trc phn tn v mt vt l (a l) dn n phn tn v mt x l thng tin. X l phn tn l mt khi nim vay mn t lnh vc tin hc. X l phn tn khc vi x l cc b v khc vi x l ni mng tnh thng nht, xuyn sut trong vic xy dng ng dng v trao i d liu gia cc trm. Tnh nng thi gian thc (real-time): Tnh nng ca mt h thng lun sn sng phn ng vi cc s kin bn ngoi v a ra p ng mt cch ng n v kp thi. Vi kin trc x l phn tn, vic p ng tnh nng thi gian thc c ci thin bi kh nng x l thng tin ti ch. Song cng nhiu vn c t ra trong vic giao tip gia cc thnh phn (real-time interprocess communication), trong vn giao thc mng ng mt vai tr quan trng. Tnh sn sng (availability) v tin cy (reliability): Mt c im ni bt so vi cc hng gii php khc l tnh sn sng cao thng qua kh nng d phng tch hp, c th la chn d phng cho tng thnh phn. Tnh sn sng, phng php giao tip s, kin trc x l phn tn, phn mm ng gi, phn cng chun ha cng nghip, tch hp cao gia cc thnh phn phn cng v phn mm l cc yu t gip cho cc h thng iu khin phn tn c tin cy cao. H tr chun (standard support): Thc ra, y khng phi l c im tiu biu ca cc h DCS truyn thng. Nhng y l mt yu cu khng th thiu c trong cc h DCS mi. c bit, s tng thch vi cc chun cng nghip l tin cho tnh nng m, cho kh nng tng tc vi cc thit b ca cc hng th ba. Cng c phn mm (software tools): Vic xy dng cc ng dng iu khin c h tr bi cc cng c lp trnh hoc cu hnh rt mnh v cc th vin phn mm ng gi chun, da theo cc chun quc t. Cc cng c phn mm iu khin gim st cng c tch hp v s dng chung mt c s d liu trong h thng. Khc vi cc gii php iu khin n l nh PLC hoc PC, ta khng phi s dng mt cng c ring, xy dng ring giao din ngi-my (HMI) v cc chc nng SCADA khc. Qu trnh to giao din ngi- my, to h thng cnh bo, to cng thc iu khin, nm trong vic pht trin ng dng, i i vi vic xy dng chng trnh iu khin cp thp.

2005, Hong Minh Sn

27

4

X L THI GIAN THC V X L PHN TN

4.1 Mt s khi nim c bn4.1.1 H thng thi gian thc

Mt h thng thi gian thc l mt h thng m s hot ng tin cy ca n khng ch ph thuc vo s chnh xc ca kt qu, m cn ph thuc vo thi im a ra kt qu phn ng vi s kin bn ngoi. H thng c li khi thi gian yu cu khng c tho mn. Mt h thng thi gian thc c cc c im tiu biu sau: Tnh b ng: H thng phi phn ng vi cc s kin xut hin vo cc thi im khng bit trc. Tnh nhanh nhy: H thng phi x l thng tin mt cch nhanh chng c th a ra kt qu phn ng mt cch kp thi. Tnh tin nh: D on trc c thi gian phn ng tiu biu, thi gian phn ng chm nht cng nh trnh t a ra cc phn ng. Tuy tnh nhanh nhy l mt c im tiu biu, nhng mt h thng c tnh nng thi gian thc khng nht thit phi c p ng tht nhanh m quan trng hn l phi c phn ng kp thi i vi cc yu cu, tc ng bn ngoi. C th ni, tt cc cc h thng iu khin l cc h thng thi gian thc. Ngc li, mt s ln cc h thng thi gian thc l cc h thng iu khin. Mt b iu khin phi a ra c tn hiu iu khin kp thi sau mt thi gian nhn c tn hiu o a qu trnh k thut v trng thi mong mun. Mt h thng truyn thng c tnh nng thi gian thc phi c kh nng truyn tin mt cch tin cy v kp thi i vi cc yu cu ca cc i tc truyn thng. Tnh nng thi gian thc ca mt h thng iu khin phn tn khng ch ph thuc vo tnh nng thi gian thc ca tng thnh phn trong h thng, m cn ph thuc vo s phi hp hot ng gia cc thnh phn .

4.1.2

X l thi gian thc

X l thi gian thc l hnh thc x l thng tin trong mt h thng m bo tnh nng thi gian thc ca n. Nh vy, x l thi gian thc cng c cc c im tiu biu nu trn nh tnh b ng, tnh nhanh nhy v tnh tin nh. c th phn ng vi nhiu s kin din ra cng mt lc, mt h thng x l thi gian thc s dng cc qu trnh tnh ton ng thi. Qu trnh tnh ton l mt tin trnh thc hin mt hoc mt phn chng trnh tun t do h iu hnh qun l trn mt my tnh, c th tn ti ng thi vi cc qu trnh khc k c trong thi gian thc hin lnh v thi gian xp hng ch i thc hin. Qu trnh tnh ton c chia thnh hai loi: 2005, Hong Minh Sn

28 Qu trnh nng cn (process): l qu trnh tnh ton c khng gian a ch ring. Qu trnh nh cn (thread): l qu trnh khng c khng gian a ch ring. Cc hnh thc t chc cc qu trnh tnh ton ng thi: X l cnh tranh: Nhiu qu trnh tnh ton chia s thi gian x l thng tin ca mt b x l. X l song song: Cc qu trnh tnh ton c phn chia thc hin song song trn nhiu b x l ca mt my tnh. X l phn tn: Mi qu trnh tnh ton c thc hin ring trn mt my tnh. Trong cc h thng iu khin, khi nim task cng hay c s dng bn cnh qu trnh tnh ton. C th ni, task l mt nhim v x l thng tin trong h thng, c th thc hin theo c ch tun hon (periodic task) hoc theo s kin (event task). V d, mt task thc hin nhim v iu khin cho mt hoc nhiu mch vng kn c chu k trch mu ging nhau. Hoc, mt task c th thc hin nhim v iu khin logic, iu khin trnh t theo cc s kin xy ra. Task c th thc hin di dng mt qu trnh tnh ton duy nht, hoc mt dy cc qu trnh tnh ton khc nhau.

4.1.3

H iu hnh thi gian thc

Cc trm iu khin trong mt h iu khin phn tn bao gi cng hot ng da trn nn mt h iu hnh thi gian thc. H iu hnh thi gian thc l mt h iu hnh h tr cc chng trnh ng dng x l thi gian thc. Bn thn h iu hnh thi gian thc cng l mt h thi gian thc theo ng ngha ca n, v vy cng c cc c im tiu biu cp. Mt h iu hnh thi gian thc bao gi cng l mt h a nhim (multi-tasking), h tr x l cnh trnh hoc/v x l song song. Lp lch, ng b ha qu trnh v giao tip lin qu trnh l cc khi nim quan trng trong mt h iu hnh thi gian thc. Phng php lp lch (Scheduling) Vic lp lch thc hin cho cc task c th c thc hin theo hai cch: Lp lnh tnh: th t thc hin cc qu trnh tnh ton khng thay i m c xc nh trc. Lp lnh ng: h iu hnh xc nh lnh trc hoc sau khi qu trnh tnh ton bt u. Tuy nhin, ta cn c mt sch lc lp lnh (strategy) p dng i vi tng tnh hung c th. C th chn mt trong nhng cch sau: FIFO (First In First Out): mt tin trnh n trc s c thc hin trc. Mc u tin c nh/ng: ti cng mt thi im, cc tin trnh c t cc mc u tin c nh hoc c th thay i nu cn. 2005, Hong Minh Sn

29 Preemptive: cn gi l chen hng, tc l chn mt tin trnh thc hin trc cc tin trnh khc. Non - Preemptive: khng chen hng. Cc tin trnh c thc hin bnh thng da trn mc u tin ca chng. Vic tnh mc u tin ca mi tin trnh c thc hin theo mt trong s cc thut ton lp lch sau: Rate monotonic: cng thng xuyn cng c u tin. Deadline monotonic: cng gp cng c u tin. Least laxity: t l thi gian tnh ton/thi hn cui cng(deadline) cng ln cng c u tin. ng b ho qu trnh Khi cc qu trnh tnh ton cng s dng mt ti nguyn loi tr ln nhau nh mt vng nh, cng vo/ra, hoc chng ph thuc ln vo nhau v d qu trnh 1 ch kt qu ca qu trnh 2... s rt d dn n tnh trng tc nghn (Deadlock), hay to ra mt tnh hung chy ua (Race Condition). Do vy vic ng b ho cc qu trnh l iu cn thit. C th thc hin vic ny theo cc phng php sau: Mutex (Mutual exclusion) Critical Section Semaphone Monitor Giao tip lin qu trnh Giao tip lin qu trnh l giao tip gia cc qu trnh tnh ton thuc cng mt h iu hnh trn mt my. C hai loi: Gia cc Thread thuc cng mt Process: s dng cc bin ton cc. Gia cc Process khc nhau hoc gia cc Thread thuc cc Process khc nhau: s dng cc phng php nh shared memory, slot, pipes, mailbox, files...

4.1.4

X l phn tn

X l phn tn gip nng cao nng lc x l thng tin ca mt h thng, gp phn ci thin tnh nng thi gian thc, nng cao tin cy v tnh linh hot ca h thng. Phn bit cc khi nim: X l cc b - ng dng n c X l cnh tranh - ng dng a nhim X l tp trung - ng dng tp trung X l ni mng - ng dng mng X l phn tn - ng dng phn tn

2005, Hong Minh Sn

30 Cn phn bit r gia ng dng mng v ng dng phn tn. Trong mt ng dng mng, cc chng trnh trn mi trm tn ti hon ton c lp vi nhau v vic giao tip gia chng c thc hin qua c ch hin (explicit communication). Web l mt ng dng mng tiu biu. Trong mt ng dng phn tn, cc chng trnh trn cc trm hp tc cht ch vi nhau thng qua c ch giao tip ngm (implicit communication) cng thc hin mt nhim v tng th ca h thng. Chc nng iu khin trong mt h iu khin phn tn c thc hin di dng mt ng dng phn tn. Cc vn ca x l phn tn Phn chia v phi hp nhim v Giao tip gia cc trm ng b ha cc qu trnh x l phn tn D phng, khc phc li

4.2 Cc kin trc x l phn tnKin trc Master/Slave Cc chc nng x l thng tin c phn chia trn nhiu trm t Mt trm ch phi hp hot ng ca nhiu trm t Cc trm t c vai tr, nhim v tng t nh nhau (tuy vi cc i tng khc nhau) Cc trm t c th giao tip trc tip, hoc khng V d tiu biu: ng dng iu khin s dng bus trng, trm iu khin l trm ch, cc vo/ra t xa hoc thit b trng l cc trm t.

Kin trc Client/Server Chc nng x l thng tin c phn chia thnh hai phn khc nhau, phn s dng chung cho nhiu bi ton c thc hin trn cc server, phn ring thc hin trn tng client. Gia cc client khng cn thit c giao tip trc tip Vai tr ch ng trong giao tip thuc v client V d tiu biu: Trong cp iu khin gim st, c th s dng mt trm ch cho vic thu thp v qun l, lu tr d liu v cnh gii bo ng, cc trm vn hnh l thc hin giao din ngi-my vi vai tr l client. Kin trc bnh ng Cc trm c vai tr bnh ng, phi hp hot ng trc tip vi nhau khng qua trung gian V d tiu biu: Trong cp iu khin, cc trm iu khin cc b phn chia thc hin chc nng iu khin cho c dy chuyn sn xut. Kin trc t tr Cc trm c vai tr bnh ng, c th hot ng tng i c lp nhng s phi hp hot ng to hiu qu cao nht. V d tiu biu: Kin trc iu khin thng minh cc h thng n tn hiu giao thng. 2005, Hong Minh Sn

31

4.3 C ch giao tipD liu ton cc (Global Data) Ging nh mt vng nh chung Mi trm u cha mt nh ca bng d liu ton cc, trong c ton b d liu cn trao i ca tt c cc trm khc Mi trm gi phn d liu ca n ti tt c cc trm, mi trm t cp nht nh ca bng d liu ton cc n gin, tin nh nhng km hiu qu p dng cho lng d liu nh, tun hon, thch hp trong kin trc bnh ng (v d gia cc trm iu khin). Hi tun t (Polling, Scanning) Mt trm ng vai tr Master C ch hi/p tun t n gin, tin nh, hiu qu cao p dng cho trao i d liu tun hon, thch hp trong kin trc Master/Slave Tay i (Peer-To-Peer) Hnh thc c lin kt hoc khng lin kt, cu hnh trc hoc khng cu hnh trc, c xc nhn hoc khng xc nhn, c yu cu hoc khng c yu cu Linh hot nhng th tc c th phc tp p dng cho trao i d liu tun hon hoc khng tun hon, thch hp cho tt c cc kin trc khc nhau. Cho/t hng (Subscriber/Publisher) Ni dung thng bo c mt trm ch cho v cc trm client t theo c ch tun hon hoc theo s kin Thng bo ch c gi ti cc trm t (c th gi ring hoc gi ng lot) Linh hot, tin nh, hiu sut cao p dng cho trao i d liu tun hon hoc khng tun hon, thch hp cho kin trc Client/Server hoc kin trc bnh ng. Hp th (Mailbox) Cc trm s dng mt mi trng trung gian nh files, mt c s d liu hoc mt chng trnh server khc ghi v c d liu Mi bc th mang d liu v m cn cc (ni dung th hoc/v ngi nhn) Gi v nhn th c th din ra ti bt c thi im no Linh hot nhng km hiu qu, kh m bo tnh nng thi gian thc p dng cho trao i d liu c tnh cht t quan trng, thch hp cho kin trc Client/Server hoc kin trc t tr. 2005, Hong Minh Sn

32

4.4 ng b ha trong x l phn tn4.4.1 ng b ha cc tn hiu vo/ra

Cu trc vo/ra phn tn s dng bus trng lm ny sinh mt vn cha c xt ti trong l thuyt iu khin s. l s khng ng b ca cc tn hiu vo/ra do thi gian tr tng knh khc nhau, kh xc nh. C hai cch gii quyt sau: t cu hnh bus v chn chu k iu khin sao cho chu k bus nh hn nhiu so vi chu k iu khin c th b qua thi gian tr tng knh khc nhau. S dng loi bus trng c h tr ng b ha cc u vo/ra, v d Profibus-DP. V d, cc lnh di y c s dng trong Profibus-DP ng b ha cc u vo/ra: FREEZE: hi nhn c lnh ny, cc DP-Slave s nhn d liu u ra gi t DP-Master v sau s khng nhn d liu u ra gi t DPMaster na cho n khi kt thc lnh FREEZE. UNFREEZE: Lnh ny lm kt thc lnh FREEZE . Cc DP-Slave s tip tc nhn d liu u ra gi t DP-Master. SYNC: Khi nhn c lnh ny,tt c hoc mt vi DP-Slave s gi d liu ti DP-Master v sau DP-Master s khng nhn d liu u vo gi t DP-Slave na cho n khi kt thc lnh SYNC. UNSYNC: Lnh ny lm ngng lnh SYNC. DP-Master s tip tc nhn d liu u vo gi t cc DP-Slave.

4.4.2

ng b ha thi gian

Gia cc trm iu khin cc b v cc trm vn hnh cn c mt s ng b ha thi gian mt cch cht ch, v y l vn lin quan h trng ti tnh chnh xc v tin cy ca cc thng tin iu khin, vn hnh, thng bo bo ng. ng b ho thi gian trong mt h iu khin phn tn, mt trm vn hnh c th c chn lm qui chiu, tt c cc trm khc ni vi bus h thng c ng b ho thi gian theo trm ny thng qua cc thng bo gi ng lat. Trong mt s h thng mng c h tr trc tip vic ng b ha thi gian, ngi ta c th chn mt thit b c chng (time master) phc v mc ch ny. Ta c th nh ngha 2 trm vn hnh lm qui chiu nhng ti mt thi im ch c mt trm mang tn hiu ng b ho, nu trm b li th trm cn li t ng hot ng. Trong cng nghip ch bin, khong thi gian chnh lch cho php gia cc trm thng trong phm vi +/-5ms. Cc thng bo thi gian cn gi ng lot theo chu k ti a 1 pht. 2005, Hong Minh Sn

33

5

CNG NGH I TNG TRONG IU KHIN PHN TN

5.1 Lp trnh hng i tngLp trnh hng i tng c coi l phng php lp trnh chun hin nay bi n c nhiu u im ln so vi cc phng php c in. Mc tiu m lp trnh hng i tng t ra l: n gin ho vic xy dng v s dng cc th vin Cho php dng li m. Nu hm th vin khng ph hp vi yu cu ca ngi lp trnh th ngi lp trnh c kh nng sa i d dng m khng cn tm hin ngn ngun, khng cn phi c m ngun ca hm trong tay. M sinh ra t thc nghim d dng c dng li trong m chnh thc. Ni khc i, ngi lp trnh c iu kin thoi mi sng to. Ci thin kh nng bo tr ca m, m phi d hiu, d sa i. Trn thc t, vic bin son ti liu bao gi cng i sau kh xa so vi m c vit ra. Cho php to ra chng trnh d m rng. C th thm chc nng cho chng trnh m khng nh hng dy chuyn n m vit. M ang c l m hi, l tin bc, khng th tr gi t cho mi chc nng thm vo. Lp trnh hng i tng phi c thc hin thng qua mt ngn ng lp trnh hng i tng. t c cc mc tiu trn, mi ngn ng lp trnh hng i tng u th hin ba khi nim: ng gi (encapsulation, packaging), a hnh (polymorphism) v tha k (inheritance). Cc ngn ng lp trnh hng i tng thng dng l C++, Java, Ada...

5.2 Phn tch v thit k hng i tngTheo dng pht trin ca cng ngh cng tin, phng php lp trnh tin ho t lp trnh khng c cu trc ln lp trnh c cu trc v ti nay l lp trnh hng i tng. Phng php phn tch, thit k phn mm cng i theo cc bc tin ho ny. Trc y, ngi ta phn tch, thit k phn mm theo kiu hng th tc (procedure-oriented) hoc hng d liu (dataoriented). Theo phng php ny, phn mm cn xy dng c chia thnh gii thut v cu trc d liu. Trong qu trnh phn tch, gii thut c phn chia thnh cc gii thut con n gin hn, cu trc d liu ln c chia thnh nhng cu trc nh hn. Qu trnh tng t cng c tin hnh trong qu trnh thit k. Phng php phn tch, thit k hng th tc hoc hng d liu c u im n gin, nhanh chng to ra kt qu (do tin hnh theo kiu t trn xung) nhng kt qu to ra khng phn nh bn cht ca th gii thc dn 2005, Hong Minh Sn

34 n cng nhc, kh thay i khi yu cu t ra thay i, kh m rng khi h thng pht trin. Phng php phn tch, thit k phn mm tin tin hin nay l hng i tng (object-oriented), trong khi c bn xy dng nn phn mm l i tng hay lp. Ni mt cch n gin, i tng l s phn nh th gii t nhin xung quanh. V d nu trong h thng iu khin c cc thit b vo/ra s/tng t nh AI, AO, DI, DO th trong phn mm cng c cc lp AI, AO, DI, DO ; trong h thng iu khin c khu iu khin PID th trong phn mm cng c lp PID,... Trong cc h thng iu khin, cc i tng c th i din cc thnh phn h thng nh: Cc thut ton iu khin X l s kin v bo ng X l mnh lnh Quan st v chn on Cu hnh vo/ra M phng Thng tin thit k Vic tru tng ho th gii t nhin thnh cc lp i tng nh vy c gi l m hnh ho hng i tng. Da trn m hnh i tng thu c, phng php phn tch, thit k phn mm hng i tng s b sung thm cc lin kt v lp i tng mi, tinh chnh li,... to ra mt m hnh i tng chi tit ca phn mm. Cui cng, ngi lp trnh s dng mt ngn ng lp trnh no (khng nht thit phi l ngn ng hng i tng) th hin m hnh i tng chi tit thnh m ngun. u im ln nht ca phn tch, thit k phn mm hng i tng khng phi nm ch to ra chng trnh nhanh tn t cng sc, m nm ch n gn vi thc t v do thc y vic ti s dng li nhng thnh qu xy dng c nh m lnh hay bn thit k.

5.2.1

Ngn ng m hnh ha thng nht UML

phc v cho cng vic m hnh ho vn l ct li ca phn tch, thit k phn mm hng i tng, ngn ng UML (unified modeling language) c s dng rng ri. UML - mt chun quc t c qun l bi t chc OMG (object management group) - l mt ngn ng ha dng trc quan ha, c t, xy dng v t liu ha h thng thin v phn mm. UML em li cho ngi s dng phng php chun vit bn thit k h thng bao trm t nhng th c th nh cc lp vit bng mt ngn ng lp trnh no , cc thnh phn phn mm c th ti s dng,... cho n nhng yu t tru tng nh chc nng ca ton b h thng. V l do ny, ngn ng UML khng ch c s dng m t, xy dng kin trc v thit k ca cc h thng phn mm, m cn l mt cng c m hnh ha thch hp cho cc h thng k 2005, Hong Minh Sn

35 thut ni chung v cc h thng iu khin ni ring. Trn Hnh 5-1 l mt biu lp UML, minh ha n gin cc lp i tng v quan h ca chng trong mt h thng iu khin.

sensor Sensor

Controller 1 sensors * 1 plant controller valves 1..*

actuator Actuator

Thermometer

ControlSystem

Valve

Plant PT2

Hnh 5-1:

M hnh ha mt h thng iu khin s dng UML

C th ni, UML l mt ngn ng m hnh ha rt mnh, a nng. Ti liu v UML c rt nhiu, v d [1][2].

5.2.2

Mu thit k

Mu thit k l s hnh thc ho ca cch tip cn ti mt vn thng gp trong ng cnh c th. Mi mu thit k m t mt gii php cho mt vn thit k c th trong mt ng cnh xc nh. Gii php ny c chng minh l hp l, s dng nhiu ln em li kt qu tt v do c tru tng ho thnh mt mu. Ni mt cch ngn gn, mu thit k l kinh nghim thit k c kt li. Bng cch dng cc mu thit k, ngi thit k khng khi thit k h thng ca mnh t u m s dng li kinh nghim c t trc, dn n cht lng thit k tt hn, tng tnh ti s dng ca bn thit k. Mt s mu thit k tiu biu l Abstract factory, Iterator, Prototype, Singleton v Template method. xy dng cc h thng phn tn hin i, ngi ta s dng cc mu thit k nh Proxy, Broker, Marshaling/Unmarshaling, Adapter v Interface Mapping. Mt tc phm c coi l kinh in vit v ti ny l [3].

5.2.3

Phn mm khung

Phn mm khung l mt dng phn mm bao gm th vin v cc mu thit k gip ngi s dng d dng to cc chng trnh ng dng bng cch b sung cc phn m ng dng c th vo cc khung c sn. im khc nhau gia mt phn mm khung vi mt th vin lp hay mt th vin hm n thun l:

2005, Hong Minh Sn

36 Mt th vin ch l mt tp hp ca cc lp hay hm hon chnh phc v mt mc ch ng dng no . M ca mt th vin lp hay hm c chng trnh ng dng ch ng gi. Mt phn mm khung cha mt s lp cha hon chnh, tc cha s dng to th nghim c ngay (lp tru tng), m bt buc phi dn xut v b sung m ng dng c th. Vic xy dng mt chng trnh ng dng phi tun theo cc mu thit k c sn. Khng nhng chng trnh ng dng gi m trong phn mm khung, m m trong phn mm khung cng ch ng gi m ng dng. C th so snh mt phn mm khung nh mt khung nh b tng c c sn theo mt thit k, ngi thi cng cn b sung cc phn tng bao, tng ngn, ca s... theo thit k , s dng cc th vin l cc vin gch, cnh ca, tm vch ngn lm sn. Mt s v d phn mm khung tiu biu l MFC (Microsoft Foundation Class), Microsofts COM (Component Object Model), Borlands VCL (Vitual Component Library).

5.3 Phn mm thnh phnPhn mm thnh phn (component software) l mt hng i mi, pht trin trn c s phng php lp trnh hng i tng. Lp trnh hng i tng cho php s dng li phn mm (di dng cc class) vo giai on bin dch (compile-time), trong khi phn mm thnh phn cho php s dng li phn mm (di dng cc component) vo c giai on bin dch v giai on chy (run-time). Do vy, theo t tng phn mm thnh phn, ngn ng lp trnh cng nh lp l th yu, giao din mi l quan trng. Ni nh vy tc l mt thnh phn phn mm (component) l cc phn mm c th c vit cc ngn ng khc nhau, c hon chnh, bin dch v ng gi, c cc giao din chun c th s dng thun tin, linh hot trong nhiu ng dng khc nhau m khng cn bin dch li. Thm ch trong mt s trng hp, vic s dng cc thnh phn phn mm c sn khng i hi lp trnh. V d ngi son tho mt vn bn c th s dng kt hp cc thnh phn phn mm c sn nh trnh son tho cng thc, v th, ... m cm tng nh tt c u nm trong chng trnh son tho vn bn. Mt s v d m hnh phn mm thnh phn tiu biu l: Delphi VC JavaBeans Visual Basic VBX ActiveX-Controls

C th ni, hu ht cc h thng pht trin ng dng trong cc h iu khin phn tn hin nay thc hin trit t tng hng i tng v phn

2005, Hong Minh Sn

37 mm thnh phn. T tng s dng khi hm, cc khi ha, cc khi chng trnh trong nhiu h thng l nhng v d tiu biu.

5.4 i tng phn tni tng phn tn cng l mt hng pht trin t nhin t phng php lun hng i tng, bn cnh phn mm thnh phn. Trong khi phn mm thnh phn quan tm ti vic ng gi cc i tng c th s dng li mt cch thun tin, th i tng phn tn tp trung vo vn kin trc cc i tng c kh nng giao tip mt cch trong sut trn cc nn v h thng mng khc nhau (giao tip ngm). Cng ging nh phn mm thnh phn, mt i tng phn tn c th thc hin mt ngn ng bt k, nhng n phi c cc giao din theo mt chun no c th hp tc vi nhau lin qu trnh v xuyn mng mt cch n gin nh hai i tng trong mt chng trnh. Ni nh vy, mt i tng phn tn cng c s dng khi bin dch, ng gi hon chnh di dng mt server. Tuy nhin, vic s dng chng c th vn i hi phi lp trnh pha client (mt i tng phn tn hoc mt chng trnh ng dng thng thng). Ngy nay, i tng phn tn v phn mm thnh phn gp nhau nhiu im, v d trong cng ngh COM/DCOM/ActiveX. Ni tm li, mt i tng phn tn l mt i tng phn mm trong mt h thng phn tn, c th c s dng bi cc chng trnh ng dng hoc cc i tng khc thuc cng mt qu trnh tnh ton, thuc mt qu trnh tnh ton khc hoc thuc mt trm khc trong mng theo mt phng thc thng nht thng qua giao tip ngm (khng ti giao thc truyn thng c th, trong sut vi h iu hnh, kin trc phn cng v h thng mng). Mt i tng phn tn c cc thuc tnh c th truy cp c t xa, c cc php ton c th gi c t xa. Mi i tng phn tn (distributed object) - bt k dng thc hin, nn trin khai v v tr ci t - u c cn cc phn bit v c th c s dng nh cc i tng ni trnh (in-process object). Li th quyt nh y l vic to dng mt ng dng phn tn c thc hin mc tru tng cao hn so vi kiu lp trnh mng c in, nh vy trn nguyn tc khng khc bit so vi to dng mt ng dng n c (stand-alone application). t c iu , ta cn s h tr hu hiu ca mt phn mm khung (framework). Hin nay c hai m hnh chun cho nhng cng trnh khung l DCOM v CORBA. CORBA cho php s dng mt cch rng ri v linh hot hn, trong khi DCOM hin nay hu nh ch s dng c trn cc h Microsoft Windows (95, 98, NT, 2000).

2005, Hong Minh Sn

38

6

KIN TRC I TNG PHN TN

Mt kin trc i tng phn tn nh ngha m hnh cc i tng phn tn, m hnh giao tip v chun giao tip gia cc i tng phn tn.

6.1 Yu cu chungMt kin trc i tng phn tn to iu kin cho vic lp trnh mt mc tru tng cao hn so vi phng php hng i tng c in. C th, im khc bit so vi lp trnh hng i tng c in nm tnh trong sut phn tn (distribution transparency), th hin qua cc c tnh sau: Trong sut v tr: Mt client khng cn bit rng i tng server nm trong cng mt qu trnh tnh ton, thuc mt qu trnh tnh ton khc trn cng mt trm hoc trn mt trm khc, cch s dng i tng server l thng nht. Ngc li cng vy. Trong sut th hin: Client khng cn quan tm ti vic i tng server c th hin bng ngn ng lp trnh no v bng phng php no, m ch cn quan tm ti giao din c th s dng. Trong sut nn: Mt client khng cn bit rng i tng server nm trn h iu hnh no, trn nn my tnh kin trc ra sao. Trong sut truyn thng: M thc hin client v cc i tng server khng lin quan ti mng truyn thng v giao thc truyn thng c th

6.2 Cc mu thit k p ng cc yu cu trn, ngi ta thng p dng cc mu thit k sau y: Proxy: Mt i tng i din cho server bn pha client, client c th s dng i tng server n gin nh vi mt i tng ni trnh (v d thng qua con tr). Broker: B phn che du chi tit v c ch truyn thng c th, to iu kin cho client/proxy v server giao tip vi nhau m khng ph thuc vo nn v h thng truyn thng bn di. Broker c mt c bn client v server. Adapter: i tng trung gian, c vai tr thch ng giao din gia broker v server, to iu kin cho vic pht trin server mt cch c lp, cng nh s dng cc server c sn (cha tun theo kin trc i tng phn tn). Marshaling/Unmarshaling: C ch thc hin m ha v ng gi cc li gi hm bn client thnh cc bc in tng ng vi c ch truyn thng cp thp, cng m gi v gii m cc bc in thnh li gi hm chi tit bn i tng server. Cc phng thc tng t cng c thc hin

2005, Hong Minh Sn

39 chuyn kt qu t server tr li client. Cc nhim v ny do proxy, server hoc/v adapter m nhim. Interface Mapping: Gii quyt vn trong sut th hin bng cch m t cc giao din bng mt ngn ng c lp IDL (Interface Description Language) v cho php nh x sang thc hin bng mt ngn ng c th.

Process A1: op ( )

Process B4: upcall( )

5: op( )

client

proxy2: marshal ( )

adapter3: dispatch( )

server

broker_A

IPC

broker_B

Hnh 6-1:

Cc mu thit k giao tip gia client v i tng server

6.3 Gii thiu chun CORBAChun CORBA [4] do t chc OMG (Object Management Group) qun l v pht trin. y l hip hi ln nht ca cc nh pht trin, sn xut v ng dng phn mm trn th gii, hin nay c gn 1.000 thnh vin. Chun CORBA a ra mt kin trc i tng phn tn cng vi cc c t ng dng cho nhiu lnh vc khc nhau, nhiu nn khc nhau v nhiu ngn ng lp trnh khc nhau. V tnh trung lp ca n, CORBA c h tr rt rng ri, c bit trong cc h thng thng tin thng mi, phn mm giao dch kinh doanh v dch v vin thng. Tuy nhin, cng do tnh c lp ca n dn n nhiu l do m CORBA khng thc s mnh cc h thng ng qui m va v nh. Hnh 6-2 minh ha cu trc m hnh CORBA, trong b phn tru tng trung gian mang tn Object Request Broker (ORB) gi vai tr quan trng nht (broker). ORB cho php khch hng (client) s dng dch v ca i tng phc v (server) m khng cn bit c th dng thc hin, nn trin khai v v tr ci t ca i tng phc v. Kin trc y c thc hin theo cc mu thit k trnh by trong phn trc.

2005, Hong Minh Sn

40

Client

Object Implementation

Dynamic Invocation

IDL Stubs

ORB Interface

Static IDL Skeleton

Dynamic Skeleton

Object Adapter

Object Request Broker Core

Hnh 6-2:

Cu trc m hnh CORBA

6.4 Gii thiu chun COM/DCOMCOM (Component Object Model) l mt m hnh i tng thnh phn, mt m hnh c s cho nhiu cng ngh phn mm quan trng ca hng Microsoft. COM nh ngha chun nh phn v c t kt ni cho vic tng tc gia cc thnh phn ca mt phn mm vi mt thnh phn khc trn cng mt qu trnh tnh ton, trn nhiu qu trnh khc nhau hay trn cc my tnh ring bit. Hng Microsoft cng hy vng mt ngy khng xa COM cng c s dng ph bin trn cc nn phn cng v h iu hnh khc nhau. COM l mt m hnh lp trnh c s i tng thit k nng cao s tng tc gia cc thnh phn phn mm, ngha l, cho php hai hoc nhiu ng dng hay cc thnh phn d dng giao tip vi nhau cho d chng c vit bi nhiu ngi khc nhau trong nhng khong thi gian khc nhau, bng nhiu ngn ng lp trnh khc nhau thm ch chy trn cc my tnh khc nhau, khng hay ci t cng mt h iu hnh. thc hin iu ny, COM nh ngha v thc thi cc k thut cho php cc ng dng kt ni vi nhau nh cc i tng phn mm. Ni cch khc, COM a ra mt m hnh tng tc m qua mt khch hng (client) c th kt ni vi cc nh cung cp dch v (object) mt cch thun tin. Vi COM, cc ng dng kt ni vi nhau v vi h thng qua cc tp hp ca cc li gi hm - xem nh l cc phng thc hay nhng hm thnh vin, cn gi l giao din. Theo cch t duy COM, mt giao din l mt quy c kiu mnh gia cc thnh phn phn mm nhm cung cp nhng lin quan d nh nhng hu dng tp cc thao tc lin quan danh ngha. Mt i tng c nh ngha ph hp vi COM l mt s th hin c bit ca i tng. Mt i tng COM ging nh mt i tng C++ nhng khc ch mt client khng truy nhp trc tip vo i tng COM m s qua cc giao din m i tng cung cp. 2005, Hong Minh Sn

41

6.4.1

Giao din

Cch duy nht truy cp d liu hoc tc ng ln mt i tng COM l thng qua giao din ca n. Mt giao din thc cht l mt nhm cc hm c sn lin quan vi nhau. C th so snh mt giao din vi mt lp c s tru tng ch gm cc hm thun o trong ngn ng C++. Giao din nh ngha c php cc hm thnh vin, gi l cc phng thc (methods), kiu tr v, s lng v cc kiu tham s. Mt giao din khng qui nh c th cc phng thc c thc hin nh th no. Thc cht vic th hin giao din l s dng con tr truy nhp vo mt mng cc con tr khc v cc con tr ny tr ti cc hm ca giao din. Thng thng, tn ca giao din c bt u bng ch ci I, v d nh IUnknown, IData... nh danh tht ca giao din th hin ch danh GUID ca n, cn tn ch thun tin cho vic lp trnh v h thng COM s s dng cc ch danh ny khi thao tc trn giao din. Thm vo , khi giao din c tn hoc kiu c th v tn ca cc hm thnh vin, n ch nh ngha lm th no mt client c th s dng giao din v nhng p ng mong i t i tng qua giao din . V d, giao din IStack vi hai hm thnh vin PUSH v POP ch nh ngha nhng thng s v kiu tr v ca hai hm ny v nhng g chng c mong i thc hin t client. C th ni, giao din l phng tin i tng a ra nhng dch v ca n. C bn im quan trng v giao din m ta cn bit: Mt giao din khng phi l mt lp theo nh ngha lp thng thng bi mt lp c th c th hin qua mt i tng cn mt giao din th khng bi n khng km theo s thc thi. Mt giao din khng phi l mt i tng bi mt giao din ch n thun l mt nhm cc hm lin quan v l chun nh phn m qua client v object c th giao tip vi nhau. Cn i tng th c th thc thi trn nhiu ngn ng vi nhiu th hin ca trng thi bn trong, v do n c th cung cp con tr n cc hm thnh vin ca giao din. Giao din c kiu mnh: Mi mt giao din u c mt nh danh ring nn ngn chn c kh nng xung t c th xy ra i vi cc tn ta t cho giao din. iu ny tng thm tnh bn vng cho chng trnh. Cc giao din c phn bit r rng: Mi s thay i nh thm hoc xo hm thnh vin, thay i ng ngha u dn ti hnh thnh mt giao din mi v c gn mt nh danh mi. Do giao din mi v c khng th xung t vi nhau cho d mi s thay i ch n thun l v ng ngha.

6.4.2

i tng COM

Mt i tng COM c th c lp trnh bng mt ngn ng thng dng nh C, C++ hoc VB. Mt i tng c th cung cp nhiu giao din. Tt c 2005, Hong Minh Sn

42 cc i tng COM u c mt giao din c bn l IUnknown. y l giao din c s cho tt c cc giao din khc trong COM m mi i tng phi h tr. Bn cnh , i tng cng c kh nng thc thi nhiu giao din khc. Cc i tng vi nhiu giao din c th cung cp cc con tr truy nhp vo nhiu bng cha cc hm. Cc con tr ny c th gi c con tr giao din. Trong COM, giao din l mt bng cc con tr ( ging nh vtable trong C++) vo cc hm c thc hin bi i tng.IUnknown

Cc giao din khc

A B

i tng

Hnh 6-3:

M hnh mt i tng COM

Trong thc t, mt con tr tr n mt giao din l mt con tr ti mt con tr tr ti bng cc con tr vo cc hm thnh vin. Tuy nhin, trnh cch din t quanh co ny khi ni v giao din ngi ta thng s dng thut ng con tr giao din thay th. Khi s thc thi giao din n gin l dng con tr tr ti mng cc con tr ti cc hm. Hnh 6-4 sau minh ha cho iu ny. Giao din IUnknown Nh trnh by trn, mi i tng COM, khng c s loi tr, u h tr giao din IUnknown. Giao din ny c ba phng thc AddRef(), Release() v QueryInterface(). Tt c cc giao din khc u dn xut t giao din IUnknown v u c cc con tr n cc phng thc ny. Hai phng thc u tnh ton s m tham chiu iu khin thi gian sng ca i tng. Khi i tng c to ln u, ta cn gi phng thc AddRef() ca i tng tng s m. Khi khng cn cn ti i tng, ta gi phng thc Release() gim s m tham chiu. Khi ngi dng cui cng gi phng thc Release(), s m gim v 0 th i tng s t hu.

2005, Hong Minh Sn

43Interface Pointer Interface Function Table pointer Pointer to Function1 Pointer to Function2 Pointer to Function3 ... Function1(...) { ... } Function2(...) { ... } Function3(...) { ... }

...

Hnh 6-4:

S thc thi con tr giao din

Ta c th thy r vn hn qua s thc thi n gin hai phng thc IUnknown::AddRef() v IUnknown::Release() di y://tng bin thnh vin cha s m tham chiu ULONG IUnknown::AddRef() { return ++m_RefCount; } //gim bin cha s m tham chiu, nu bng 0 th hu i tng ULONG IUnknown::Release() { --m_RefCout; if (m_RefCount == 0) { delete this; return 0; } return m_RefCount; }

Khi ta c mt con tr n i tng th thc cht, nhng g ta c ch l mt con tr n mt trong s cc giao din ca n, cn l giao din no th li ph thuc vo cch m ta c con tr . T con tr vo mt giao din, ta c th truy cp c con tr vo cc giao din khc m i tng h tr. i tng c th hoc khng h tr giao din m ta quan tm, nhng mi i tng u c m bo h tr giao din Iunknown nn ta c th yu cu cc giao din khc qua phng thc IUnknow::QueryInterface(). Cc giao din c nh danh bi cc IIDs (Interface IDs) v d nh IID_IUnknown ca giao din IUnknown. Khi ta gi phng thc QueryInterface(), ta gi IID ca giao din m ta cn cho n v mt con tr n tham s u ra. Nu i tng h tr giao din yu cu, n s tr li on m bo thnh cng S_OK (nh ngha l 0) v t vo tham s u ra m ta cung cp con tr n giao din yu cu. Nu i tng khng h tr giao din ny n bo li v t tham s u ra l NULL. Ta xt mt s thc thi n gin sau:HRESULT IUnknown::QueryInterface (REFIID riid , LPVOID * ppv) { //kim tra IID xem i tng c h tr giao din yu cu khng,

2005, Hong Minh Sn

44//nu h tr ta tng s m tham chiu, a vo bin u ra cung cp // mt con tr n giao din, v bo rng thnh cng if (riid == IDD_IUnknow) { AddRef(); *ppv = (LPVOID) this; return S_OK; } //nu khng h tr giao din ta t bin u ra cung cp l NULL v // tr v mt m thng bo li else { *ppv = NULL; return E_NOINTERFACE; } }

Quan h gia i tng v cc giao din Cc client ch kt ni qua con tr ti cc giao din. Khi mt client truy nhp vo mt i tng, client ch n thun thng qua con tr giao din. Con tr giu i ni dung ca thao tc bn trong, ta khng th thy chi tit v i tng m ch c th thy thng tin v trng thi ca chng. i tng c th thc thi nhiu giao din. Mt lp thc thi i tng c th thc thi nhiu giao din, v d qua phng php a tha k.

6.4.3

Giao tip gia client v object

Cch thc ca s giao tip Trc khi s dng mt i tng COM trong mt ng dng, ta cn khi to c ch COM trong ng dng bng li gi CoInitialize(...) v sau to i tng COM mong mun. Client kt ni vi object thng qua con tr giao din v khng bao gi truy nhp trc tip vo object. Khi cn s dng dch v no ca i tng, client hiu rng n cn c con tr n mt hay nhiu giao din ca i tng. to mt i tng COM v nhn mt con tr vo giao din, ta c th gi mt trong hai hm CoCreateInstance() hoc CoCreateInstanceEx() vi cc tham s xc nh i tng.

Client Application

Object Interface Pointer

Hnh 6-5:

Giao tip gia i tng v khch hng

Trong mt s trng hp, bn thn client s ng vai tr mt object v cung cp cho cc i tng khc nhng chc nng gi cc s kin hoc a ra cc dch v ca n. Lc ny client l mt i tng thc thi cn object l mt khch hng.

2005, Hong Minh Sn

45Application Object Object Application

Hnh 6-6:

Giao tip gia hai i tng

Giao tip trn cng mt qu trnh tnh ton Khi client v i tng COM cng nm trn mt qu trnh tnh ton th client s kt ni trc tip vi object qua con tr giao din.Qu trnh client client server object

Hnh 6-7:

Giao tip gia i tng v khch hng trn cng qu trnh

Giao tip lin qu trnh Nu client v object khng cng nm trn mt khng gian a ch hay nm trn cc my tnh khc nhau th COM s thit lp mt i tng i din (proxy) bn pha client v mt i tng gc (stub) bn pha object. Proxy v stub s kt ni vi nhau qua knh giao tip (channel). Khi , client s thc hin li gi dch v trong khng gian a ch ca n tc l giao tip trc tip vi proxy. Proxy s thu thp (marshal) cc thng s, gi chng n stub qua knh giao tip. Stub thc hin li gi n i tng dch v, ng gi kt qu v a v cho proxy.Qu trnh client client Proxy server proxy StubQu trnh dch v cc b hay t xa

server object

COM Engine

Hnh 6-8: Giao tip gia i tng v khch hng trn hai qu trnh khc nhau

2005, Hong Minh Sn

46

6.4.4

Ngn ng m t giao din

IDL (Interface Description Language) l mt ngn ng kiu mnh dng m t giao din ca i tng COM, c lp vi ngn ng lp trnh. C php ca ngn ng ny khng phc tp so vi mt ngn ng lp trnh. Khi xy dng mt i tng COM, ta cn m t cc phng thc ca giao din bng cch s dng ngn ng ny. Sau khi tp xong file m t giao din ny, ta cn lu n dng *.idl chng trnh dch c th hiu c. Chng trnh dch (IDL-Compiler) s dch sang mt ngn ng lp trnh, v d C++. Khi mt giao din s c chuyn sang thc hin bng mt cu trc thch hp trong ngn ng lp trnh, v d mt lp thun o trong C++.

6.4.5

M hnh i tng thnh phn phn tn DCOM

DCOM (Distributed COM) m rng COM cho vic giao tip gia cc i tng phn tn, thuc cc chng trnh chy trn nhiu my tnh khc nhau trn mng LAN, WAN hay Internet. Vi DCOM, cc ng dng c th phn tn trn nhiu v tr em li s thun li cho chnh ng dng. Ngy nay khi ngi ta ni ti COM l cng thng bao hm DCOM trong . DCOM l mt cng ngh l tng cho nhng ng dng nhiu tng lp bi v n cho php nhng thnh phn ActiveX lm vic ngang qua mng. Nhiu ngi c th pht trin thm cng mt thnh phn m khng cn phi lo lng v lp trnh mng, tnh tng thch h thng hoc s hp nht ca nhng thnh phn xy dng t nhng ngn ng khc nhau. N dn ti h thp gi thnh v lm gim s phc tp ca vic phn tn cc ng dng thnh phn.

ClientCoCreateInstance()

Proxy Security Provider DCE RPC

Stub Security Provider DCE RPC

Component

COM Runtime(Remote) Activation

Protocol Stack

Protocol StackCoCreateInstance()

SCMDCOM networkprotocol

SCM

Hnh 6-9: Giao tip gia i tng v khch hng trn hai my khc nhau vi DCOM

2005, Hong Minh Sn

47 Khi cc i tng trn cc my tnh khc nhau, DCOM n gin thc hin s thay th truyn thng lin qu trnh cc b bi giao thc mng. Hnh di y minh ha r nt cch thc giao tip gia cc i tng nm trn hai my tnh khc nhau. Th vin COM Run-Time cung cp nhng dch v hng i tng ti khch hng v thnh phn mun giao tip vi nhau ng thi s dng RPC v nh cung cp an ton to chun ni mng ng gi tun theo giao thc truyn thng cho DCOM. Mt ng dng client c th to mt i tng trn mt my tnh khc qua hm API CoCreateInstance(). Ta xt mt v d n gin sau:HRESUL hr = CoCreateInstance( CLSID_CData, // nh danh lp ca i tng yu cu NULL, CLSCTX_REMOTE_SERVER, // dch v t xa c yu cu &si); // tham s u ra cha con tr giao din

2005, Hong Minh Sn

48

7

CC M HNH NG DNG IU KHIN PHN TN

7.1 IEC-61131IEC (International Electrotechnical Commission) l mt t chc ton cu bao gm cc hi ng cc quc gia. Mc tiu ca t chc ny l thc y cng vic chun ho trong lnh vc in v in t. IEC 61131 l tiu chun v b iu khin kh trnh PLC v cc thit b ngoi vi i km vi n. Chun IEC 61131 bao gm 9 phn, trong cc phn 1 n 5 l quan trng nht: Phn 1 (General Information): a ra cc nh ngha chung v cc c tnh chc nng tiu biu cho mi h thng iu khin s dng PLC, v d c ch thc hin tun hon, nh qu trnh, thit b lp trnh v giao din ngi-my. Phn 2 (Equipment requirements): t ra cc yu cu in hc, c hc v chc nng cho cc thit b; nh ngha phng php kim tra v th nghim cc kiu thit b tng ng. Cc yu cu c nh ngha l nhit , m, cung cp ngun, khng nhiu, phm vi tn hiu logic v sc bn c hc ca cc thit b. Phn 3 (Programming languages): nh ngha cc ngn ng lp trnh cho cc thit b iu khin kh trnh. Ngoi ba ngn ng kinh in l biu hnh thang (Ladder Diagram, LD), biu khi chc nng (Function Block Diagram, FBD) v lit k lnh (Instruction List, IL), v mt ngn ng bc cao kiu vn bn c cu trc (Structured Text, ST) th mt phng php lp trnh ha phc v biu din cc thut ton iu khin trnh t l SFC (Sequential Function Chart) cng c chun ha. Phn 4 (Guidelines for users): a ra cc nguyn tc ch o cho ngi s dng trong cc qu trnh ca mt d n, t phn tch h thng cho ti la chn thit b, vn hnh v bo tr h thng. Phn 5 (Communication): cp ti phng php truyn thng gia cc PLC cng nh gia PLC v mt thit b khc trn c s cc khi hm chun. Cc dch v truyn thng ny m rng chun ISO/IEC 9506-1/2, thc cht l mt tp con trong cc dch v c qui nh trong MMS.

7.1.1

M hnh phn mm

Mi PLC ti mt thi im bt k ch c mt cu hnh (configuration) no . Mt cu hnh bao gm mt hay nhiu ti nguyn (resource) bn trong c trng cho kh nng x l tn hiu ca PLC. Mi ti nguyn bao gm t nht mt chng trnh (program) hot ng di s iu khin ca tc v (task). Chng trnh c xy dng nn t cc khi chc nng (function block) hoc cc yu t ngn ng khc (c c thy 5 ngn ng lp trnh c nh ngha 2005, Hong Minh Sn

49 trong phn ny). Cc bin ton cc (global variable) v li truy cp (access path) l nhng c ch giao tip trong chng trnh v gia cc ti nguyn vi nhau.

C O N FIG U R ATIO N R ESO UR C E TAS K TAS K R ESO UR C E TAS K TAS K

PR O G RA M

PR O G RA M FB FB

PR O G RA M

PR O G RA M FB FB

G LO BA L and D IR EC TLY and IN STAN C E-SPEC IFIC

R EP R ESE NTE D VAR IA BLES IN ITIA LIZA TIO N S

AC C ES S P ATH S

C om m unication function

(See IE C 1131-5) Execution control path

or FB

Variable access paths Function block Variable

Hnh 7-1:

M hnh phn mm theo IEC 61131-3

7.1.2

M hnh giao tip

Nh biu din trong Hnh 7-2, gi tr ca bin c th c truyn trc tip trong ni b chng trnh bng cch kt ni u ra ca n v ngn ng ny ti u vo ca n v ngn ng khc. Mi lin kt ny c biu din mt cch trc quan trong cc ngn ng ha hoc n trong cc ngn ng vn bn.FB1 a FB2 b

Hnh 7-2:

Giao tip bn trong chng trnh

Gi tr ca bin cng c th c truyn gia cc chng trnh trong cng mt cu hnh thng qua bin ton cc kiu nh bin x biu din trong Hnh 7-3. Bin ny c khai bo l EXTERNAL i vi tt c cc chng trnh s dng n. 2005, Hong Minh Sn

50CONFIGURATION C PROGRAM A VAR_EXTERNAL x: BOOL; END_VAR FB1 FB_X a x VAR_GLOBAL x: BOOL; END_VAR x b PROGRAM B VAR_EXTERNAL x: BOOL; END_VAR FB2 FB_Y

Hnh 7-3: Giao tip gia cc chng trnh trong cng mt cu hnh bng bin ton cc

Hnh 7-4 biu din cch giao tip a nng nht thng qua khi chc nng giao tip. Chi tit v loi khi chc nng ny c m t trong IEC 61131-5, y ch lu rng, s dng khi chc nng truyn thng, gi tr ca bin c th c truyn gia cc b phn ca chng trnh, gia cc chng trnh trong cng mt cu hnh hay trong cc cu hnh khc nhau, thm ch gia chng trnh chy trong PLC vi cc h thng khc khng phi PLC.

CONFIGURATION C PROGRAM send SEND SD1 a

CONFIGURATION D rcv1 PROGRAM RCV RD1 FB2 FB_ b

FB1 FB_

Hnh 7-4:

Giao tip qua khi chc nng

Sau cng, b iu khin kh trnh v h thng khng phi PLC c th truyn d liu qua li thng qua li truy cp nh biu din trong Hnh 7-5, s dng cc c ch nh ngha trong IEC 61131-5.

2005, Hong Minh Sn

51CONFIGURATION C P1 PROGRAM A FB1 FB_X a Z 'CSX' VAR_ACCESS CSX: P1.Z : REAL READ_ONLY; PROGRAM B CONFIGURATION D

TO_FB2 READ RD1 VAR_1

FB2 FB_Y b

Hnh 7-5:

Giao tip qua ng dn truy cp

7.2 IEC-61499IEC 61499 l tiu chun lin quan n vic s dng cc khi chc nng vi t cch l cc module phn mm trong h thng o lng - iu khin phn tn. ng t quan im hng i tng, mi khi chc nng c coi l mt i tng phn tn vi mt chc nng trong h thng. Chun IEC 61499 bao gm 3 phn trong phn 1 l quan trng nht. IEC 61499-1 nh ngha kin trc chung ca h thng o lng - iu khin, khi chc nng ng vai tr ct li, di dng cc m hnh tham kho. C tt c 8 m hnh c nh ngha nh trnh by di y.

7.2.1

M hnh h thng

Chun IEC m t h thng o lng - iu khin qu trnh cng nghip dng mt tp hp cc thit b kt ni li v lin lc vi nhau thng qua mt hay nhiu mng truyn thng nh trong Hnh 7-6 di y. Cc mng ny c th c t chc theo th bc.H thng mng truyn thng

Thit b 1

Thit b 2ng dng A

Thit b 3

Thit b 4

ng dng B ng dng C

Qu trnh k thutHnh 7-6: M hnh h thng theo IEC 61499

2005, Hong Minh Sn

52 Mi chc nng c thc hin bi h thng o lng - iu khin c m hnh ha bng mt ng dng nh trong hnh v trn. Mt ng dng c th nm trong mt thit b duy nht, nh ng dng C trong hnh v, hoc phn tn trn mt s thit b, nh cc ng dng A v B. V d, mt ng dng c th cha mt hay nhiu vng iu khin trong vic ly mu u vo c thc hin bi mt thit b, tnh ton iu khin c thc hin bi thit b khc cn vic chuyn i u ra li c tin hnh bi thit b th ba.

7.2.2

M hnh thit b

Nh biu din trong Hnh 7-7, mi thit b cha trong n t nht mt giao din, ngoi ra c th c hoc khng cha cc ti nguyn v mng khi chc nng.Lin kt truyn thngLung d liu v s kin

Ranh gii thit b Giao din truyn thng

Ti nguyn X

Ti nguyn Y ng dng A

Ti nguyn Z

ng dng C

ng dng C

Giao din qu trnh

Qu trnh k thut

Hnh 7-7: M hnh thit b theo IEC 61499 (v d thit b 2 trong Hnh 7-6.

Giao din qu trnh l mt thnh phn ca thit b c nhim v nh x gia cp iu khin bn di (thit b o tng t, thit b vo/ra phn tn, ...) v cc ti nguyn bn trong thit b. Thng tin trao i gia cp iu khin bn di v cc ti nguyn th hin di dng lung d liu v s kin. Giao din truyn thng cng l mt thnh phn ca thit b c nhim v nh x gia mng truyn thng pha trn v cc ti nguyn bn trong thit b. Cc dch v cung cp bi giao din ny bao gm : Biu din cc thng tin truyn ti ti nguyn thnh dng d liu v s kin Cung cp cc dch v khc h tr vic lp trnh, t cu hnh, d li, ...

7.2.3

M hnh ti nguyn

Chun IEC coi ti nguyn l mt n v chc nng, cha trong mt thit b vn c quyn c lp iu khin hnh vi ca mnh. Ti nguyn c th c 2005, Hong Minh Sn

53 to ra, t cu hnh, th hin bng tham s, khi ng, xa, ... m khng nh hng n cc ti nguyn khc bn trong thit b. Chc nng ca ti nguyn l nhn d liu v/hoc s kin t giao din truyn thng hoc giao din qu trnh, x l d liu/s kin ri gi tr li d liu/s kin ti giao din truyn thng/qu trnh theo yu cu ca ng dng s dng ti nguyn.

Giao din truyn thng nh x truyn thngS kin D liuKhi chc nng giao din dch v Thut ton Khi chc nng giao din dch v

ng dng cc b (hoc phn cc b ca ng dng phn tn

nh x qu trnh Giao din qu trnh Cc hm dch v

Hnh 7-8:

M hnh ti nguyn

Nh trong , ti nguyn c m hnh ha bao gm cc thnh phn sau : Mt hoc nhiu ng dng cc b (hay thnh phn cc b ca mt ng dng phn tn). Cc bin v s kin c qun l trong phn ny cc bin u vo, bin u ra, s kin u vo, s kin u ra ca cc khi chc nng thc hin php ton cn cho ng dng. Thnh phn nh x qu trnh c nhim v nh x d liu v s kin gia ng dng v giao din qu trnh. Nh biu din trong hnh, iu ny c thc hin bi cc khi chc nng phc v giao tip. Khi chc nng phc v giao tip cng l khi chc nng thng thng nhng c chuyn bit ha cho nhim v ny. Thnh phn nh x truyn thng c nhim v nh x d liu v s kin gia ng dng v giao din truyn thng. Nh biu din trong hnh, iu ny cng c thc hin bi cc khi chc nng phc v giao tip. B phn lp lch c nhim v iu khin s thc thi ca cc khi hm bn trong ng dng cng nh dng d liu truyn gia chng tun theo nhng yu cu v thi gian v trnh t quyt nh bi s xut hin ca cc s kin, lin kt gia cc khi hm v thng tin khc nh chu k v mc u tin.

7.2.4

M hnh ng dng

Mi ng dng c m hnh ha dng mt mng cc khi chc nng (function block network). Mng ny c cu thnh t cc nt mng l cc 2005, Hong Minh Sn

54 khi chc nng v lin kt gia cc nt mng l lin kt d liu (data connections) v lin kt s kin (event connections). Mt ng dng c th c phn tn trn nhiu ti nguyn thuc mt hay nhiu thit b. Mi ti nguyn s dng cc mi lin h nhn qu ch ra bi ng dng quyt nh phn ng thch hp i vi cc s kin pht sinh t giao din truyn thng, giao din qu trnh, t trong bn thn chnh ti nguyn hoc t ti nguyn khc. Cc phn ng ny bao gm : S lp lch v thc thi thut ton (bn trong ti nguyn) Vic thay i cc bin Sn sinh cc tn hiu Tng tc vi giao din truyn thng v giao din qu trnh ng dng c nh ngha bng cch ch ra mi lin h gia cc khi chc nng cha bn trong n nh minh ha trong hnh v, c th l ch ra lung s kin (event flow) v lung d liu (data flow). Chnh lung s kin l ci quyt nh vic lp lch v thc thi ca mi ti nguyn bn trong ng dng.Lung s kin

Lung d liu

Hnh 7-9:

M hnh ng dng

7.2.5

M hnh khi chc nng

Mi khi chc nng thc ra l mt bin th hin (function block instance) ca mt kiu khi chc nng no (function block type) cng tng t nh mi i tng l mt bin th hin ca mt lp no . Cc c tnh ca khi chc nng: Tn bin (l tn ca chnh khi chc nng ) v tn kiu (l tn ca kiu khi chc nng m n thuc) Mt tp cc u vo s kin, dng nhn cc s kin n t cc lin kt s kin vi bn ngoi. Chnh cc s kin u vo s nh hng ti vic thc thi thut ton bn trong khi chc nng. Mt tp cc u ra s kin, dng y cc s kin ra cc lin kt s kin vi bn ngoi ty thuc v s thc thi ca thut ton v mt s yu t khc Mt tp cc u vo d liu, chng c nh x ti cc bin u vo tng ng 2005, Hong Minh Sn

55 Mt tp cc u ra d liu, chng c nh x ti cc bin u ra tng ng D liu ni b, chng c nh x ti tp cc bin ni b Cc c trng v chc nng, c xc nh bng cch kt hp gia d liu ni b vi thut ton ca khi chcu vo s kin Tn khi Lung s kiniu khin thc hin (che giu)

u ra s kin

Lung s kin

Tn kiu Lung d liuThut ton (che giu) D liu ni b (che giu)

Lung d liu

u vo d liu

u ra d liu

Nng lc ti nguyn (Lp lch, nh x truyn thng, nh x qu trnh)

Hnh 7-10:

M hnh khi chc nng

Thut ton bn trong khi hm, v nguyn tc, khng nhn thy c t bn ngoi, tr phi c ngi cung cp khi hm m t theo mt cch no . Thm na, khi hm c th cha bn trong n cc bin ni b hay cc thng tin v trng thi tn ti khng i gia nhng ln gi thut ton ca khi hm nhng chng cng khng truy cp c t bn ngoi. Mi kiu khi chc nng l mt yu t phn mm ch r c tnh ca tt c cc bin th hin thuc kiu , bao gm : Tn kiu S lng, tn, tn kiu v trt t ca cc u vo s kin v u ra s kin S lng, tn, kiu d liu v trt t ca cc bin u vo, bin u ra v bin ni b c t kiu khi chc nng ngoi phn chung k trn cn c thm phn nh ngha chc nng c trng ca khi ph thuc vo loi khi c th. C c thy 3 loi khi chc nng : Khi chc nng c bn l n v chc nng nh nht, khng th phn chia hn c na Khi chc nng kt hp (Siu khi) l loi khi chc nng hp thnh t nhiu khi chc nng khc nh hn Khi chc nng dch v giao tip l loi khi chc nng cung cp cc dch v giao din gia cc khi chc nng khc vi nhau hoc gia ti 2005, Hong Minh Sn

56 nguyn v mng truyn thng v gia ti nguyn v qu trnh cng ngh c iu khin. i vi kiu khi chc nng c bn, chc nng c trng ca n c din t bng cch m t thut ton bn trong khi hot ng da trn gi tr ca cc bin u vo, bin u ra, bin ni b to ra gi tr mi cho cc bin u ra v bin ni b nh th no, cng nh mi lin h gia s khi ng, thc thi v kt thc ca thut ton vi s xut hin ca cc s kin ti u vo v s kin u ra ca khi. i vi kiu khi chc nng kt hp, c t kiu cn bao gm cc lin kt d liu v lin kt s kin gia nhng khi chc nng thnh phn bn trong khi chc nng kt hp. i vi kiu khi chc nng phc v giao tip, chc nng c trng c m t bng cch nh x cc dch v c bn m n cung cp thnh cc u vo s kin, u ra s kin, u vo d liu, u ra d liu ca n.

7.2.6

M hnh phn tn

Mt ng dng c th c phn tn bng cch phn b cc khi chc nng ca n vo cc ti nguyn khc nhau nm trn mt hay nhiu thit b. Bi v chi tit bn trong khi chc nng l khng nhn thy c i vi ng dng s dng n cho nn khi chc nng phi l n v nh nht khng phn chia c i vi s phn tn ny. Ngha l, khng th chia nh khi chc nng hn na phn tn trn nhiu ti nguyn; cc thnh phn cha bn trong khi chc nng phi nm trn cng mt ti nguyn. Cc mi lin h v chc nng gia cc khi chc nng khng c php b nh hng bi s phn tn. Tuy nhin, so vi ng dng tp trung, cc yu t v thi gian v tin cy ca chc nng truyn thng c nh hng ng k ti cc yu t v thi gian v tin cy ca ton ng dng phn tn.

7.2.7

M hnh qun l

Vic qun l cc ti nguyn bn trong mt thit b c m hnh theo mt trong hai cch Trong thit b, c mt ti nguyn c to ring qun l tt c nhng ci cn li. N cung cp mt tp cc dch v qun l cho cc ti nguyn khc dng chung. Mi ti nguyn c mt b phn qun l ca ring mnh. Ni cch khc, cc dch v qun l c phn tn ra khp tt c cc ti nguyn bn trong thit b.

7.2.8

M hnh trng thi hot ng

Bt k h thng no cng c thit k, bn giao cng vic, a vo vn hnh, duy tr bo dng v cui cng sau khi hon thnh nhim v - c hy b. iu ny c m hnh ha bng ci gi l vng i ca h thng. 2005, Hong Minh Sn

57 n lt mnh, cc n v chc nng cu thnh nn h thng nh thit b, ti nguyn, ng dng mi ci cng c vng i ring ca mnh. h tr cho n v chc nng ti mi thi im trong vng i ca n, cc hnh ng khc nhau phi c thc hin. phn bit xem hnh ng no c th thc hin v duy tr tnh ton vn ca n v chc nng, cc trng thi hot ng phi c nh ngha, v d ang hot ng, C th cu hnh, np, dng, ... Mi trng thi hot ng ca mt n v chc nng ch r hnh ng no c chp nhn v hnh vi mong mun tng ng. H thng c th c t chc theo cch mt khi chc nng no c th s hu hoc nhn c quyn thay i trng thi ca khi chc nng khc. Mt c im ni bt ca IEC 61499 l n yu cu cc cng c phn mm tun theo chun phi c kh nng trao i thng tin vi nhau. C th l IEC 61499-2 yu cu nh sn xut thit b phn cng hay th vin phn mm phi cung cp thng tin cn thit cho vic s dng sn phm ca h mt cch hiu qu trong khi vn m bo quyn s hu tr tu. iu ny c thc hin bng cch s dng ngn ng XML. IEC 61499-2 nh ngha mt tp cc th (tag) v cu trc ti liu XML chun, da vo nh sn xut m t sn phm ca mnh. Tun theo mt tp th chung, cc sn phm c th lm vic trc tip vi nhau (interoperability).

2005, Hong Minh Sn

58

8

MT S CHUN GIAO TIP CNG NGHIP

8.1 MMSMMS (Manufactoring Message Specification) l mt chun quc t cho vic xy dng lp ng dng theo m hnh qui chiu OSI. Chun ny c ngha c bit trong cc h thng truyn thng cng nghip. V c bn, MMS qui nh mt tp hp cc dch v chun cho vic trao i d liu thi gian thc cng nh thng tin iu khin gim st. Cc dch v ny cng nh cc giao thc tng ng c chun ha trong ISO/IEC 9506. MMS c xut x t MAP (Manufactoring Automation Protocol), mt giao thc do hng General Motors khi xng pht trin vo u nhng nm 80. Mc d MAP khng tr thnh giao thc truyn thng thng nht cho cng nghip t ng ha, n tc ng c tnh cht nh hng ti cc pht trin sau ny. Trn c s ca MAP, cc dch v truyn thng c nh ngha trong MMS to c s quan trng trong vic xy dng lp ng dng trong nhiu h thng bus trng. Mt s v d nh FMS (Fieldbus Message Specification) ca PROFIBUS, PMS (Pe