Chng 3:

GII THIU THUT TON IU KHIN

PID

3.1. Gii thiu b iu khin PID:

B iu khin PID l mt b iu khin vng kn c s dng rng ri trong

cng nghip. S dng b iu khin PID iu chnh sai lch gia gi tr o c ca

h thng (process variable) vi gi tr t (setpoint) bng cch tnh ton v iu chnh gi

tr iu khin ng ra.

S mt h thng iu khin dng PID:

Mt b iu khin PID gm 3 thnh phn: P (proportional) to tn hiu iu

khin t l vi sai lch (error e), I (integral) to tn hiu iu khin t l vi tch phn

theo thi gian ca sai lch, v D (derivative) to tn hiu iu khin t l vi vi phn

theo thi gian ca sai lch.

a) Khu P:

Khu P to ra tn hiu iu khin t l vi gi tr ca sai lch. Vic ny c thc

hin bng cch nhn sai lch e vi hng s KP gi l hng s t l.

Khu P c tnh da trn cng thc:

Vi: Pout: gi tr ng ra

KP: hng s t l

Hnh 1 S h thng iu khin dng PID

e: sai lch: e = SP PV

S khi ca khu P:

Hm truyn: p pG (s) = K

Nu ch c khu P th trong mi trng hp sai s tnh lun xut hin, tr khi gi

tr u vo ca h thng bng 0 hoc bng vi gi tr mong mun. Trong hnh sau th

hin sai s tnh xut hin khi thay i gi tr t.

Hnh 2 p ng ca khu P

Nu gi tr khu P qu ln s lm cho h thng mt n nh.

b) Khu I:

Khu I cng thm tng cc sai s trc vo gi tr iu khin. Vic tnh tng

cc sai s c thc hin lin tc cho n khi gi tr t c bng vi gi tr t, v kt

qu l khi h cn bng th sai s bng 0.

Khu I c tnh theo cng thc:

Vi: IOUT: gi tr ng ra khu I

Ki: h s tch phn

e: sai s: e = SP PV

S khi khu I:

Hm truyn:

I

I.

KU(s) 1G(s) = = =

E(s) s T s

Khu I thng i km vi khu P, hp thnh b iu khin PI. Nu ch s dng

khu I th p ng ca h thng s chm v thng b dao ng.

Hnh sau ch ra s khc bit gia khu I v PI:

Hnh 3 p ng ca khu I v PI

Ta c th nhn thy l khu I lm cho p ng ca h thng b chm i rt nhiu,

cn khu PI gip trit tiu sai s xc lp.

c) Khu D:

Khu D cng thm tc thay i sai s vo gi tr iu khin ng ra. Nu sai

s thay i nhanh th s to ra thnh phn cng thm vo gi tr iu khin. iu ny ci

thin p ng ca h thng, gip trng thi ca h thng thay i nhanh chng v mau

chng t c gi tr mong mun.

Khu D c tnh theo cng thc:

Vi: DOUT: ng ra khu D

KD: h s vi phn

e: sai s: e = SP PV

S khi khu D:

Hm truyn:

( )( )

( )d

U sG s K s

E s

Khu D thng i km vi khu P thnh b PD, hoc vi PI thnh b PID.

Hnh 4 p ng ca khu D v PD

Theo hnh trn, b PD to p ng c thi gian tng trng nh hn so vi b P. Nu

gi tr D qu ln s lm cho h thng khng n nh.

d) Tng hp ba khu B iu khin PID:

B iu khin PID l cu trc ghp song song gia 3 khu P, I v D.

Phng trnh vi phn ca b PID l tng:

P I D

de(t)u(t) = K e(t)+ K e(t)dt+ K

dt

S khi:

p ng ca b PID:

Hnh 5 p ng ca khu P, PI v PID

e) Ri rc ha b iu khin PID:

B iu khin s khng th ly mu lin tc theo thi gian, n cn c ri rc

mt vi mc. Khi cho h s ly mu ngn bn trong thi gian vi phn c th t c xp

x mt sai phn c gii hn v tch phn qua vic ly tng. Chng ta s quan tm mi

dng mt thi im, v sai s c tnh mi khong ly mu:

e(n) = X(n) Y(n)

B PID ri rc c sai s, tnh ton v xut ng ra iu khin theo mt khong

thi gian xc nh (khng lin tc) thi gian ly mu T. Thi gian ly mu cn nh hn

n v thi gian ca h thng.

Khng ging cc thut ton iu khin n gin khc, b iu khin PID c kh

nng xut tn hiu ng ra da trn gi tr trc ca sai s cng nh tc thay i sai

s. iu ny gip cho qu trnh iu khin chnh xc v n nh hn.

Hnh 6 S khi PID

Hm truyn ca h thng:

Hm chuyn i:

Tnh gn ng theo cng thc:

Vi n l bc ri rc ti t.

Kt qu thu c:

Vi:

3.2. Thit k b iu khin PID:

Lut iu khin thng c chn trn c s xc nh c m hnh ton hc ca

i tng phi ph hp vi i tng cng nh tha mn yu cu ca bi ton thit k.

Trong trng hp khng th xc nh c m hnh ton hc ca i tng, c th

tm lut iu khin cng nh cc tham s ca b iu khin thng qua thc nghim.

Ziegler v Nichols a ra phng php xc nh thng s ti u ca b PID l da

trn th hm qu ca i tng hoc da trn cc gi tr ti hn thu c qua thc

nghim.

a) S dng hm qu ca i tng:

Phng php ny cn c tn l phng php th nht ca Ziegler Nichols. N c

nhim v xc nh cc thng s Kp , TN , TV cho cc b iu khin P, PI v PID trn c

s i tng c th m t xp x bi hm truyn t dng:

t-T sKeG(s) =

Ts+ 1

Sao cho h thng nhanh chng v trng thi xc lp v vt l max

khng vt qu

mt gii hn cho php, khong 40% so vi t

thh )(lim)( :

%40)(

max

maxh

h

Ba tham s Tt (thi gian tr), K (h s khuch i) v T (hng s thi gian qun tnh)

ca m hnh xp x c th xc nh c gn ng t th hm qu h(t) ca i

tng. Nu i tng c dng nh hnh 7a m t th t th hm h(t) ta c ra c:

-Tt l khong thi gian tn hiu ra h(t) cha c phn ng ngay vi tn hiu kch thch 1(t) ti u vo.

-K l gi tr gii hn t

thh )(lim)(

-Gi A l im kt thc khong thi gian tr , tc l im trn trc honh c honh

bng Tt. Khi T l khong cn thit sau Tt tip tuyn ca h(t) ti A t c gi tr K.

a) b)

Hnh 7 Xc nh tham s cho m hnh xp x bc nht c tr

Trng hp hm qu h(t) khng c dng l tng nh hnh 7a, nhng c dng

gn ging nh hnh ch S ca khu qun tnh bc 2 hoc bc n nh m t hnh 7b th ba

tham s K, Tt, T c xc nh xp x nh sau :

-K l gi tr gii hn )(h .

-K ng tip tuyn ca h(t) ti im un ca n. Khi Tt s l honh giao im

ca tip tuyn vi trc honh v T l khong thi gian cn thit ng tip tuyn i

c t gi tr 0 ti c gi tr K.

Nh vy ta thy iu kin p dng c phng php xp x m hnh bc nht c

tr ca i tng l i tng phi n nh, khng c dao ng v t nht hm qu ca

n phi c dng ch S. Sau khi c cc tham s cho m hnh xp x ca i tng, ta

chn cc thng s ca b iu khin theo bng sau :

B iu khin KP TN TV

P

tTK

T

.

_ _

PI

tTK

T

.9,0 tT

3

10

_

PID

tTK

T

.2,1 t

T.2 tT.5,0

Bng 1 Tnh ton thng s b iu khin

T suy ra :

H s tch phn :

PI

N

KK =

T

H s vi phn :

D P VK = K .T

b) S dng cc gi tr ti hn thu c t thc nghim:

Trong trng hp khng th xy dng phng php m hnh cho i tng th

phng php thit k thch hp l phng php thc nghim. Thc nghim ch c th

tin hnh nu h thng m bo iu kin: khi a trng thi lm vic ca h n bin

gii n nh th mi gi tr ca tn hiu trong h thng iu phi nm trong gii hn cho

php.

Phng php ny cn c tn l phng php th hai ca Ziegler Nichols. iu

c bit l phng php ny khng s dng m hnh ton hc ca i tng iu khin,

ngay c m hnh xp x gn ng.

Cc bc tin hnh nh sau :

-Trc tin, s dng b P lp vo h kn (hoc dng b PID v chnh cc thnh phn

KI v KD v gi tr 0). Khi ng qu trnh vi h s khuch i KP thp, sau tng dn

KP ti gi tr ti hn Kgh h kn ch gii hn n nh, tc l tn hiu ra h(t) c

dng dao ng iu ha. Xc nh chu k ti hn Tgh ca dao ng.

Hnh 8 M hnh iu khin vi Kgh

Hnh 9 Xc nh h s khuch i ti hn

- Xc nh thng s ca b iu khin theo bng sau :

B iu khin KP TN TV

P 0,5 Kgh _ _

PI 0,45 Kgh 0,83 Tgh _

PID 0,6 Kgh 0,5 Tgh 0,125 Tgh

Bng 2: Thng s b iu khin theo thc nghim

3.3. Lp trnh PID trong S7-200

a) Lnh vng lp PID

Lnh vng lp PID tnh ton vng lp PID (PID Loop) theo cc u vo v nhng

thng s t bng c nh a ch bi TBL.

Nhng li c th c gy nn bi lnh ny

-Bit c bit SM4.3 = 1 : li Run Time

-Li 0006: a ch gin tip

-Bit c bit SM1.1 = 1: li trn (Overflow).

Lnh PID Loop (Proportional, Integral, Derivative Loop) c s dng tnh ton

vng lp PID. Lnh ny ch c thc hin nu nh nh ca ngn xp bng 1 trong STL

hay c Power Flow trong LAD. Lnh ny c hai ton hng : [TBL] l a ch byte u

tin ca mt bng d liu cn [LOOP] l mt s nm trong khong t 0 n 7. iu ny

cng c ngha l ch c ti a 8 lnh PID Loop c th c s dng trong mt chng

trnh. Nu c hai bng khc nhau i na cng vn nh hng n nhau v c th gy

nhng hu qu khng lng trc c.

Bng d liu ca lnh PID Loop bao gm 09 tham s dng iu khin hot ng

ca vng lp:

-gi tr tc thi (current value)

- gi tr k trc (current and previous value) ca bin iu khin (process vafiable),

-gi tr yu cu (setpoint),

- gi tr x l (output-u ra ca PID),

-h s khuch i (Gain),

-thi gian ly mu (sample time),

-h s tch phn (integral time reset),

-h s vi phn (derivative time rate) v

- integral sum (bias)

thc hin lnh ny mt tn sut ly mu xc nh, n phi hoc l c t trong

mt ngt thi gian hoc l c thc hin trong chng trnh chnh qua kim sot bi

mt b nh thi. ng thi, thi gian ly mu tng ng phi c a vo bng d

liu ca lnh.

Trong STEP 7 Micro / Win 32, chng ta c th s dng PID Wizard to thut ton

vi PID cho mt mch iu khin kn bng cch chn Tools Instruction Wizard -> PID t

menu chnh.( c trnh by trong chng 2 phn PID)

trng thi n nh, mt b iu khin PID s iu chnh sao cho sai s gia gi tr

yu cu (setpoint SP) v gi tr iu khin (process variable PV) bng 0. Nguyn l ca

mt b iu khin nh vy th hin trong phng trnh sau:

Trong :

-M(t) : u ra ca PID (i lng x l) nh mt hm theo thi gian

-Kc: hng s khuch i

-e: sai s e = SP PV

-Mi : gi tr ban u ca PID

Nhm mc ch p dng b iu khin PID trn my vi tnh hay PLC ni ring v

trong k thut s ni chung, chng ta phi tin hnh ri rc ha phng trnh nu trn.

C th l ly mu v lng t ha cc bin. Phng trnh c vit li nh sau:

Trong :

-Mn : u ra ca PID (i lng x l) thi im ly mu n

-Kc : hng s khuch i

-en : sai s thi im ly mu n

en = SPn - PVn

-en-1 : sai s thi im ly mu ngay trc (n 1)

en-1 = SPn-1 - PVn-1

-Ki : hng s khuch i ca thnh phn tch phn

-Mi : gi tr ban u ca PID

-Kd : hng s khuch i ca thnh phn vi phn

T phng trnh ny ta nhn thy rng, nu nh thnh phn t l (proportional) ch l

hm ca sai s thi im ly mu th thnh phn vi phn (differential) l hm s ca sai

s thi im ly mu u tin cho n thi im ly mu hin ti. Trong k thut s,

lu li tt c cc sai s l iu khng th thc hin, cng nh tht s khng cn thit.

V gi tr x l lun c tnh ton mi thi im ly mu, k t thi im u tin,

nn ch cn lu li gi tr k trc ca sai s v thnh phn tch phn. Phng trnh c

n gin thnh:

Trong :

-Mn : u ra ca PID (i lng x l) thi im ly mu n

-Kc : hng s khuch i

-en : sai s thi im ly mu

en = SPn - PVn

-en-1 : sai s thi im ly mu ngay trc (n 1)

en-1 = SPn-1 - PVn-1

-Ki : hng s khuch i ca thnh phn tch phn

-Mx : gi tr thnh phn tch phn thi im ly mu k trc (n-1)

-Kd : hng s khuch i ca thnh phn vi phn

Mt cch vit khc ca phng trnh:

Mn = MPn + MIn + MDn

Trong :

-Mn : u ra ca PID (i lng x l) thi im ly mu n

-MPn : thnh phn t l ca u ra PID thi im ly mu n

-MIn : thnh phn tch phn ca u ra PID thi im ly mu n

-MDn : thnh phn vi phn ca u ra PID thi im ly mu n

b) Ta ln lt xt n tng thnh phn mt ca i lng x l:

**Thnh phn t l

Thnh phn t l (proportional) MP l tch ca hng s khuch i Kc vi sai s e.

Trong Kc c trng cho nhy ca u ra PID ( Kc cng ln, b iu khin PID cng

nhy) cn e l sai s gia i lng yu cu (setpoint SP) v i lng thc t (process

variable PV). Phng trnh biu din:

MPn = Kc * (SPn - PVn)

Trong :

-MPn : thnh phn t l ca u ra PID thi im ly mu n

-Kc : hng s khuch i

-SPn : i lng yu cu ti thi im ly mu n

-PVn : i lng thc t ti thi im ly mu n

**Thnh phn tch phn

Thnh phn tch phn (integral) MI t l vi tng cc sai s qua thi gian, th hin

bng phng trnh:

MIn = KC * Ts / Ti * (SPn - PVn ) + MX

Trong :

- MIn: thnh phn tch phn ca u ra PID thi im ly mu n

- Kc: hng s khuch i

- Ts: thi gian ly mu

-Ti: h s tch phn

-SPn: i lng yu cu ti thi im ly mu n

- PVn: i lng thc t ti thi im ly mu n

-MX: gi tr ca thnh phn tch phn thi im ly mu k trc (n-1), cn c gi l

integral sum hay bias.

Sau khi tnh ton gi tr MIn, bias MX c thay th bi chnh gi tr MIn vi kh

nng c th b iu chnh hoc ct (chn gii hn), iu ny s c ni r phn sau.

Gi tr ban u ca bias MX, Mi thng c ly l gi tr ca u ra b PID ngay trc

thi im thc hin lnh PID u tin. Cc hng s khc nh hng n thnh phn ny

l : Kc hng s khuch i, Ts thi gian ly mu v Ti h s tch phn l c trng

cho nh hng ca thnh phn ny ln ton b i lng x l.

**Thnh phn vi phn

Thnh phn vi phn (differential) MD t l vi thay i ca sai s, th hin qua

phng trnh:

MDn = KC * Td / Ts * ((SPn - PVn ) - (SPn - 1 - PVn - 1 ))

Vi c tnh c qun tnh ca mi h vt cht, chng ta c th gi thit rng i lng

thc t PV khng bao gi c s thay i mt cch gin on. Tuy nhin i lng yu

cu th c th tng gim gy khc (do tnh trn l thuyt). V bn cht ton hc, thnh

phn vi phn l php ly o hm nn nhng s thay i gin on c th gy nn cc gi

tr v cng ln u ra. trnh hin tng ny, trong phng trnh trn ta gi thit

SPn = SPn 1 v c th vit:

MDn = KC * Td / Ts * (PVn - 1 - PVn)

Trong :

- MDn: thnh phn vi phn ca u ra PID thi im ly mu n

- Kc: hng s khuch i

- Ts: thi gian ly mu

- Td: h s vi phn

- SPn: i lng yu cu ti thi im ly mu n

- SPn-1: i lng yu cu ti thi im ly mu n-1

- PVn: i lng thc t ti thi im ly mu n

- PVn-1: i lng thc t ti thi im ly mu n-1

Nh vy trn thc t khng cn nh sai s thi im ly mu k trc m ch cn

nh i lng thc t. Trong ln tnh ton u tin PVn-1 = PVn

Ty theo ng dng thc t, c th b bt thnh phn trong b iu khin PID ch

khng nht thit phi bao gm c ba thnh phn, chng hn c th to b iu khin t

l (P) hay b iu khin ch cha cc thnh phn t l v tch phn (PI). S la chn ny

da trn cch t cc tham s.

Nu mun b thnh phn tch phn (b I), ta chn h s tch phn bng v cng (T i =

0). Trong trng hp ny, thnh phn tch phn vn khng nht thit bng khng m c

th bng mt gi tr khng i thng qu gi tr bias MX ban u.

Nu mun b thnh phn vi phn (b D), ta chn h s vi phn bng khng (Td =

0.0). Nu mun b thnh phn t l (b P), ta chn h s khuch i bng khng (Kc =

0.0). Trong trng hp ny, v cc hng s ca cc thnh phn tch phn v vi phn c

tnh theo Kc nn i vi nhng thnh phn y, Kc c hiu l bng 1.0

Mt b iu kin PID c hai u vo: i lng yu cu v i lng thc t. y l

nhng i lng tht trong ng dng nh nhit , p sut, tc ,. a vo tnh

ton trong mt b iu khin, chng phi c o, chuyn i v gi tr thch hp v

chun ha (nu cn). Cc bc ny u cn thit cho mt b iu khin PID, b ny i

hi cc gi tr u vo l nhng gi tr s thc (du phy ng) nm trong khong t 0.0

n 1.0

Thng thng, nhng gi tr o c c a vo PLC qua cc u vo tng t

(quy v in p trong khong 0 10VDC hoc dng in 0 20mADC) thnh nhng gi

tr s nguyn 16 bit c du. Trc ht nhng gi tr ny phi c i thnh cc s thc

32 bit (du phy ng).

Bc tip theo l chun ha v khong [0.0 1.0] theo phng trnh:

NNorm = (NRaw / Span) + Offset

Trong :

NNorm : l gi tr chun ha, i din cho mt i lng tht

NRaw : l gi tr thc cha chun ha, i din cho mt i lng tht

Span : l hiu ca gi tr ln nht c th c tr i gi tr nh nht c th c ca gi tr

cha chun ha. Trong S7 200 thng l 32000 0 = 32000 i vi cc i lng

khng i du (unipolar) v khi offset = 0.0 hay 32000 (-32000) = 64000 i vi

cc i lng c th va c gi tr dng va c gi tr m (bipolar) v khi Offset =

0.5

Mt cch logic chng ta thy rng cn phi c qu trnh ngc li vi qu trnh trn

i vi gi tr u ra ca b iu khin PID. Ngha l bin i v a v thang gi tr

thch hp cho u ra t gi tr u ra chun ha trong khong 0.0 n 1.0. Phng

trnh thut ton

RScale = (MNorm - Offset) * Span

Trong :

-RScale l gi tr thch hp cho u ra, i din cho mt i lng tht

-MNorm l gi tr u ra chun ha, i din cho mt i lng tht

-Span l hiu ca gi tr ln nht c th c tr i gi tr nh nht c th c ca gi tr

cha chun ha. Trong S7 200 thng 32000-0 = 32000 i vi cc i lng khng

du (unipolar) v khi Offset = 0.0 hay 32000 (-32000) = 64000 i vi cc i

lng c th va c gi tr dng va c gi tr m (bipolar) v khi Offset = 0.5.

Chng ta thng ni v vng lp iu khin thun khi h s khuch i dng (Kc >

0) hay vng lp iu khin o (nghch) khi h s khuch i m (Kc < 0). Trong trng

hp khng c thnh phn P (Kc = 0), ta xt du ca cc h s Ti v Td

Cc gi tr yu cu v gi tr thc t (bin iu khin) l nhng u vo ca b iu

khin PID, do cc trng tng ng vi chng trong bng d liu ca PID s khng b

thay i bi lnh ny.

Ngc li trng tng ng vi u ra c cp nht bi PID. N s b ct (chn)

nu vt ra ngoi khong cho php [0.0 1.0].

Nu c s dng thnh phn tch phn (I), bias cng c cp nht v li c dng

lm u vo cho ln ly mu k tip. Tuy nhin n c th c iu chnh trong trng

hp u ra b chn (v vt ra ngoi khong [0.0 1.0]) theo phng trnh sau:

-Khi u ra ln hn 1.0 : MX = 1.0 - (MPn + MDn )

-Khi u ra nh hn 0.0: MX = - (MPn + MDn )

Trong :

-MX l gi tr bias c iu chnh

-MPn : l gi tr thnh phn t l (P) ca u ra thi im ly mu n

-MDn l gi tr thnh phn vi phn (D) ca u ra thi im ly mu n

-Mn l gi tr ca u ra thi im ly mu n

Bng s iu chnh ny, gi tr u ra s c a v khong hp l. Gi tr bias cng

b chn trong khong [0.0 1.0] v ghi vo bng d liu cho ln ly mu tip theo s

dng.

Gi tr bias trong bng d liu c th thay i c ngay trc khi thc hin lnh PID

nhng phi ch y l mt s thc nm trong khong [0.0 1.0].

Gi tr i lng thc t ca ln ly mu trc c lu li trong bng d liu tnh

ton thnh phn vi phn, khng bao gi c thay i gi tr ny.

Mt b iu khin PID c th hot ng mt trong hai ch : Auto hoc Manual.

Thc ra khng c ch hot ng no c xy dng sn cho PID trong S7-200. S

tnh ton ch c thc hin khi c dng nng lng (powerflow) n u En (enable)

ca b PID. PID c xem nh hot ng ch Auto khi n thcu75 hin tnh ton

mt cch tun hon lin tc. Trong trng hp ngc li, PID c xem nh hot ng

ch Manual. Vn chng ta cn xt n l s chuyn i m bo tnh lin tc t

ch Manual sang ch Auto. iu i hi u ra c tnh trong ch Manual

phi c ghi vo u vo thi im chuyn i: khi dng nng lng thay i t 0 ln

1. Lc CPU s thc hin mt lot thao tc cn thit:

-t gi tr yu cu bng gi tr thc t: SPn = PVn

- t gi tr k trc ca gi tr thc t: PVn-1 = PVn

-t bias bng gi tr u ra: MX = Mn

Bit nh ca mt b PID c gi tr mc nh l 1 (ON), c t khi CPU khi ng

hay chuyn t ch STOP sang ch RUN. iu cng c ngha l khi b PID

c thc hin ln u tin, CPU khng nhn bit s chuyn i trng thi ca dng

nng lng t 0 ln 1 v do khng thc hin cc thao tc nu trn.

Lnh PID l mt lnh n gin nhng rt mnh trong vic tnh ton thut ton PID.

Nu cn mt s tnh nng khc, v d nh bo ng hay nhng thay i c bit, c th

s dng cc lnh khc can thip. Khi chng trnh s dng c bin dch, li bin

dch c th xut hin nu a ch bng tham s [TBL] hoc ton hng [LOOP] ca b PID

vt ra ngoi phm vi cho php (out of range). Mt s phm vi cho php khng c

kim tra, v vy ngi lp trnh phi ch . Chng hn nh nhng gi tr yu cu v thc

t phi l cc s thc nm trong khong t 0.0 n 1.0 cng nh cc gi tr thc t k

trc hay bias, nu c s dng, khng c vt ra ngoi khong [0.0 1.0]. Nu li

xut hin trong qu trnh tnh ton thut ton PID, bit c bit SM1.1 (overflow) s bng

1 v qu trnh tnh ton b dng li. Trong nhng trng hp nh vy , u ra ca b PID

c th cha c hon thnh, v vy ngi lp trnh phi ch kim tra bit c bit ny

s dng u ra mt cch hp l cng nh iu chnh cc u vo nu cn thit. nh

dng bng cc tham s ca mt b PID bao gm 36 bytes nh sau:

-0 Bin x l (process variable) PVn : Bao gm bin x l, chun ho t 0 n 1.

-4 im t (setpoint) SPn : Bao gm im t, chun ho t 0 n 1.

-8 Output Mn : Ng ra PID c tnh ton, chun ho t l t 0 n 1.

-12 li vng (Gain) Kc : Bao gm li l hng s t l. C th dng hoc m.

-16 Thi gian ly mu (Sample time) Ts : Thi gian ly mu, n v l giy, l s dng.

-20 Thi gian tch phn (Integral time) hoc reset Ti : Cha thi gian tch phn v tc

(rate), n v tnh: pht, l s dng.

-24 Thi gian vi phn (Derivative time) hoc reset TD : Cha thi gian vi phn v tc

(rate), n v tnh: pht, l s dng.

-28 Mc ngng (bias) MX : Bao gm mc ngng v gi tr tng vi phn nm t 0 n

1.

-32 Bin x l trc PVn-1 : Tr s o gi tr ca bin x l trc c lu t lc

thc thi lnh PID cui cng.