ISA 77.22 – Working Copy Ta ble of Contents 1.0 Scope.. .................................................................................................................. ....1 2.0 Pur pos e....................................................................................................................1 .0 !efin itio ns.... ...........................................................................................................2 ".0 Concepts............................................................................................................. .....#.0 Sy$bo ls.... ...............................................................................................................%.0 &lock !efin itions.....................................................................................................%.1 !ri'e s(............................................................................................................... ...%.1.1 )otor Control * Sin gle spee+, $ai nta ine+ control out put -.. .............................%.1.2 )/ *openclose oper ati on, $o$entary output-............................................%.2 Te ro up Contro l &lo cks ................................................................................. ..%.2.1 T3 o !e'ice Cont rol ler ................................................................................. %.2. 2 Tr ee !e'ice Controlle r.. ............................................................................7.0 Se4uenc e Contr oller ............................................................................................... ..5.0 Pla nt Auto$ation.....................................................................................................Anne6 A 8eferences..........................................................................................................Anne6 & – Tutorial Infor$ation..........................................................................................Anne6 C 9igures................................................................................................................Anne6 ! – Application :6a$ples.......................................................................................Anne6 : – Plant configuration............................................................................................Anne6 9 – ;otes – Startup Se4uence.................................................................................utline of 77.22 ;otes( 1. Tis out line follo3s t e general for$at of ote r 77 serie s +ocu$ents for consistency. Preface an+ cre+its to fol lo3 te sa$e for$at . 2. I<$ n ot sur e 3y te 9i gures are at te ba ck in Anne 6 C. I 3ou l+ a'e tougt it $ore con'enient for te rea+er to a'e tese i$be++e+ in te te6t for $ore rea+y reference. Is tere a reason for not i$be++ing te 9igures= CONTENTS 1.0 Scope Tis tecnical report pro'i+es gui+ance in te +esign an+ application of auto$ation strategies for plants 3itfuel input rati ngs of 2# )W ter$al or greater . Tis tecnical report a++resses te ter$inology, +ocu$entation, an+ relate+ $eto+ology for +e'eloping auto$ation strategies. 2.0 Purpose
%.1.1 )otor Control *Single spee+, $aintaine+ control output-...............................
%.1.2 )/ *openclose operation, $o$entary output-............................................%.2 Te roup Control &locks...................................................................................
;otes(1. Tis outline follo3s te general for$at of oter 77 series +ocu$ents for
consistency. Preface an+ cre+its to follo3 te sa$e for$at.
2. I<$ not sure 3y te 9igures are at te back in Anne6 C. I 3oul+ a'e tougt it$ore con'enient for te rea+er to a'e tese i$be++e+ in te te6t for $ore rea+y
reference. Is tere a reason for not i$be++ing te 9igures=
CONTENTS
1.0 Scope
Tis tecnical report pro'i+es gui+ance in te +esign an+ application of auto$ation
strategies for plants 3it fuel input ratings of 2# )W ter$al or greater. Tis tecnical
Te purpose of tis tecnical report is to pro'i+e a+'ice an+ gui+ance for te
+e'elop$ent of fossil po3er plant auto$ation.
3.0 Definitions
>+efinitions go ere? I a'e taken a first atte$pt at a fe3>
I;T:8@CS are also signals acting to protect e4uip$ent fro$ +a$age, to pre'ent
unsafe operation, to pre'ent process upset, or any co$bination of tese. Wat+ifferentiates te$ fro$ trips is tat te actions +o not sut +o3n te e4uip$ent or
process in 4uestion. Te process or e4uip$ent is protecte+ by oter $eans.
I;T:8@CS are sub+i'i+e+ into t3o types( per$issi'e an+ correcti'e. Tese ter$s
are analogous to Bpassi'e an+ acti'e so$eti$es use+ by oters.
P:8)ISSI/: I;T:8@CS per$it or pre'ent a control action, 3eter $anual
or auto$atic, for$ occurring if te progra$$e+ criteria are not $et. Te salient
feature is tat action is pre'ente+ an+ tus noting occurs, inclu+ing te unsafeactions. An e6a$ple of a per$issi'e interlock is not per$itting a pu$p to be
starte+ if its suction isolation 'al'e is close+.
C88:CTI/: I;T:8@CS a'oi+ unsafe situations by taking a correcti'e
action. Tis is +istinctly +ifferent fro$ te per$issi'e interlock 3ic $erely pre'ent actions. Typically, te correcti'e interlock initiates a $inor operation
necessary to preclu+e an unsafe con+ition fro$ occurring.
An e6a$ple is starting an au6 lube oil pu$p upon tripping of te pri$arye4uip$ent. Starting te lube oil pu$p constitutes taking a positi'e action, as
oppose+ to te purely passi'e action of a per$issi'e interlock. Te ter$
C88:CT/: I;T:8@C is restricte+ to $ini$al progra$$e+ protecti'eactions. Diger le'els of auto$ation 3ic acti'ates e4uip$ent are not
consi+ere+ interlocks.
S:EF:;CI; refers to progra$$e+ actions 3ic inclu+e $ultiple pieces of
e4uip$ent. Typically, S:EF:;CI; co'ers a nu$ber of actions, nor$ally perfor$e+
se4uentially, 3it eac step co$$encing upon co$pletion of te pre'ious. Altoug
se4uencing can consist of a linear series of connecte+ actions, parallel steps are also per$itte+ 3en concurrent actions are +esire+. Do3e'er, a te function of a +iscrete step
soul+ be retaine+, so tat eac block alar$s in+i'i+ually.
Te +istinction bet3een a correcti'e interlock an+ a se4uence is subtle. 9or tis
+ocu$ent, a correcti'e interlock is restricte+ to actions necessary to protect e4uip$ent or
processes follo3ing an e'ent. A se4uence is initiate+ to acco$plis a series of preprogra$$e+ steps
T8IPS are signals causing a protecti'e action 3ic places e4uip$ent in a safe state,
$ost co$$only sut +o3n. Tis action $ay be to protect e4uip$ent fro$ +a$age, to
pre'ent unsafe operation, to pre'ent process upset, or any co$bination of tese. T8IPS
are spontaneous actions resulting fro$ te logic respon+ing to process an+ e4uip$ent
fee+back. Classic e6a$ples of trips are to sut off a pu$p 3ic as insufficient ea+, or a $otor 3ic is +ra3ing e6cess current. Trips respon+ 3it action to a process
con+ition.
A++itional Clarification
Consi+ering 3at an e6acting process logic +esign is, te ter$inology use+ is re$arkablyloose. Consistent ter$s 3ill be use+ in tis +ocu$ent, an+ since +efinitions are generally
A single con+ition *e.g. lo3 pu$p suction le'el- $ay constitute bot a trip an+ a per$issi'e, +epen+ing upon process con+itions. If te pu$p is running, it $ust be
stoppe+ , an+ te occurrence of tis lo3 signal $ust be progra$$e+ as a pu$p trip.
Con'ersely, if te pu$p is not running, starting te pu$p is $erely pre'ente+. ;ote tereis a tacit assu$ption tat tere is no ar$ in not starting te pu$p – if te conse4uences
of not starting te pu$p are 3orse tan te risks of running, ten suc an interlock 3oul+
not be use+.
4.0 Concepts
Altoug tis cogniti'e capability is taken for grante+, progra$$ing a +igital co$puterto perfor$ a si$ilar task as pro'en re$arkably +ifficult. Te $in+ appears to a'e
+ifficulty keeping si$ultaneous track of 'ery e6plicit ite$s, e'en 3en tose ite$s are
in+i'i+ually straigtfor3ar+. Progra$$ing re4uires e6actly tese sorts of skills, an+ tusas pro'en to be an iterati'e an+ error prone process.
nce te co+e e6cee+s $ore tan a fe3 +oGen lines in lengt *an+ so$e 3oul+ argue
e'en less tan tat-, errors – or bugs – ten+ to creep in. Tis is so per'asi'e tat aB+ebugging pase is consi+ere+ a nor$al part of progra$$ing. !CS progra$$ing is
no e6ception, an+ it is 4uite possibly e6acerbate+ by te nee+ for co$preension of te
pysical plant process to be controlle+.
;o tecni4ue can fully eli$inate u$an error. Do3e'er, engineers 3o +esign logic in
an organiGe+, logical $anner generally pro+uce syste$s 3ic start up faster an+ 3itless confusion tan teir a+ oc progra$$ing counterparts. Tis +ocu$ent atte$pts to
lay fort principles 3ic organiGes an+ stan+ar+iGes logic +esign, to assist in goo+
+esign. Te intent is bot te +esign engineers, startup personnel an+ en+ operations
users 3ill fin+ te !CS pro+uct easier an+ $ore consistent.
Tis +ocu$ent intro+uces te concepts of ierarcical control. Te reasoning bein+ tis
approac is e6plaine+ an+ te ter$s are +efine+. In+i'i+ual control blocks are ten+iscusse+, signals +efine+ an+ operation e6plaine+. 9inally 'arious progra$$ing
e6a$ples are gi'en to clarify usage an+ progra$$ing tecni4ue.
oo+ logic +esign *an+ progra$$ing- is caracteriGe+ by being organiGe+, consistent an+
obHecti'es. :6ceptions e6ist, but tese soul+ be reser'e+ for applications 3icspecifically re4uire +e'iations in or+er to acco$plis te re4uire+ control.
Start by +escribing te 9C principles.
Principles of ierarcical control.
Alar$ing consistency
Alar$ Strategy
A goo+ alar$ strategy 3ill pro'i+e te operator 3it a $a6i$u$ a$ount of useful
infor$ation, 3ile $ini$iGing nuisance alar$s an+ Binfor$ation o'erloa+. A
ierarcical control strategy not only supports a goo+ progra$$ing $eto+ology, it alsolen+s itself to a goo+ alar$ sce$e.
9un+a$entally, ierarcical control can be tougt of as a collection of functions blocks.
:ac block as a specific purpose, an+ controls specific actions for e4uip$ent belo3 it.Te block soul+ alar$ 3en it fails to acco$plis its re4uire+ actions. Tis re4uires
tat a block by +esigne+ 3it te fee+back necessary to $onitor its actions.
9ee+back is so$eti$es not pro'i+e+ as a cost sa'ing $easure. Te a++itional
infor$ation pro'i+e+ to te !CS, 3ile useful, $ay incur a++itional costs 3ic are
+ifficult to Hustify. Tis co$pro$ise affects te engineer<s ability to apply te alar$ principles consistently.
A co$$on e6a$ple is pro'i+ing position fee+back on a $o+ulating control 'al'e. If
position fee+back is a'ailable, ten te operator can be alerte+ tat te control 'al'e $aynot be functioning correctly. Witout suc fee+back, te !CS cannot +eter$ine tat its
output +e$an+ signal to te 'al'e is not being follo3e+. If tere are so$e process
conse4uences resulting fro$ tis lack of control, e'entually so$e para$eter 3ill +e'iateunacceptably resulting in an alar$. Te operator is ten left to +e+uce te cause base+ on
is kno3le+ge an+ e6perience 3it te process.
Current tren+s to3ar+ +igital instru$ent co$$unications alle'iate te cost i$pact since
perfor$ance +ata *$onitoring fee+back- is a'ailable fro$ te en+ controller. A 'al'e
3it a 9iel+bus or Profibus controller can pro'i+e te re4uire+ fee+back at no
incre$ental cost oter tan te effort of progra$$ing. Wen i$ple$ente+ as part of a
consistent progra$, tis effort soul+ be negligible.
!igital co$$unications fro$ in+i'i+ual instru$ents $ay per$it a furter le'el af alar$
+etail. Specifically, infor$ation concerning te nature of te e4uip$ent failure in te
fiel+ $ay be pro'i+e+. Do3e'er, tis infor$ation $ay be $ore useful to $aintenance personnel tan to operations staff. If fiel+ e4uip$ent as faile+, ten te auto$ation
an+or operators $ust co$pensate to per$it te process to continue operation. Wy tis
e4uip$ent as faile+ is secon+ary to process consi+erations. Accor+ingly, signals 3icrelate to +etails of e4uip$ent failure soul+ not be processe+ as alar$s to $ini$iGe
operator loa+. Tese +etails soul+ be a'ailable to te operators as part of e'entalar$
lists, but soul+ not constitute a source of a++itional +istraction +uring operation.
Certain alar$s are generate+ for infor$ation 3ic is e6ternal to te group or e4uip$ent
control logic. Tese inclu+e process 'ariations *pressure, te$perature-, trouble alar$s
fro$ syste$s a'ing little infor$ation in te !CS, e6ternal e'ents *fire alar$-, etc.
Suc alar$s +o not fit 3ell into te general ierarcical structure, but are noneteless
essential since te !CS cannot $onitor all possible causes of failure.
:$pasis $ust be place+ on generating alar$s 3ic are(
Abbre'iations are te nor$ in an alar$ list, but $ust be una$biguous. Te alar$
3or+ing $ust also
Te 9C *ierarcical- part
•
rapic representation• 9C block +efinition
• Sy$bology con'entions
• Signals +efinition
• Se4uencer blocksse4uence tripsnearest safe state
Tere are alrea+y ISA practices co'ering te follo3ing(
• Plant $aster control
• 8unbacks
• 1P& startstop se4uences
•
@ist of ar+3are re4uire+ for support• Alar$ $anage$ent
5.0 Symbols
We nee+ to a++ress o3 to +epict te control reco$$en+ations. ter 77 seriesstan+ar+s use SA)A representation? 3e nee+ to fin+ a goo+ 3ay to present our i+eas. In
* This input is used to defeat the alarming (and therefore any associated automaticactions) of a step, with stopping the entire sequence. The sequence loc! remains acti"e,
and passes through the sequence on signal to the sequence complete signal, while the
equipment command remains off. # typical application is for starting equipment in a
sequence, and then turning the same equipment off later in the same sequence. The sequence string can then remain acti"e without the first loc! going into alarm.
* Typically used to initiate susequent sequence loc!
Status(
1. Se4uence step faile+ to co$plete *$aintaine+-
Alar$s(
1. Se4uence step faile+ to co$plete
2.
Se4uence &locks
Se4uencer blocks are typically use+ to eiter start or stop e4uip$ent in a se4uential$anner. ;or$ally, a separate string of se4uencer blocks is use+ for te start an+ te stop
se4uence. Te co$$an+ outputs of te se4uencer blocks $ust not affect te e4uip$entunless tat particular se4uence string is in ser'ice.
%.0 Pl&nt 'utom&tion
@e'el of auto$ation – to 3at e6tent are 3e going= Single button start=
Do3 to organiGe – suggest startup an+ sut+o3n be togeter for eac plantconfiguration.
Suggeste+ organiGation(roup control Syste$s
• Co'er in+i'i+ual plant syste$s ere – te ones 3ic len+ te$sel'es to group
*ierarcical- control(
o 9ee+3ater syste$
o Con+ensate syste$
o &oiler airgas *9!I! fans-
o PA syste$
o ter Bstan+alone type applications
• Te o'erall plant *an+ so$e syste$s- 3ill re4uire
o 'erall startup an+ sut+o3n se4uenceso 9uel se4uencing *$ills, burners-
Anoter 4uestion is o3 $uc to co'er. &elo3 is a list of te $aHor plant types. Wecoul+ a++ress te +ifferent types by
a- a'ing a separate stan+ar+ *or section of a stan+ar+- for eac configuration,
Te si$plifie+ figure belo3 +epicts a si$ple group control for 6#0J con+ensate pu$ps.
:ac pu$p as an in+i'i+ual $otor +ri'e $o+ule. Per$issi'es an+ trips are use+ ere for e4uip$ent protection. enerally, tis protection is connecte+ at te lo3est le'el, an+
superse+es any control co$$an+s, 3eter auto or $anual. :ac pu$p $ay be operate+
in $anual $o+e, or place+ in auto for by iger le'els of auto$ation.
Te group of tree pu$ps is controlle+ by a tree +e'ice controller, 3ic starts or stops
te in+i'i+ual +ri'es as re4uire+. Internal to tis block are containe+ i$portant control
features(
• Te nu$ber of operating pu$ps is co$pare+ against te re4uire+ nu$ber, an+
pu$p*s- starte+ an+ stoppe+ accor+ingly.
• Te +ri'e priority se4uence *or+er of pu$p starting- $ay be $anually set, but
3ill auto$atically a+Hust for te una'ailability of te subor+inate +ri'e, as+eter$ine+ fro$ te +ri'e $o+ule Ba'ailable status signal
• Te +ri'e priority se4uence transfers to auto in a bu$pless $anner, so as to
I reco$$en+ 3e target te CC 26261 an+ PC 161 for our first +raft +ocu$ent.
Denrik<s notes, fyi(
Tis +raft outline is largely a collection of $y 3riting to +ate, 3it so$e input fro$
oters. Tis $eans it as no consensus, an+ I a$ sure te 77.22 $e$bers 3ill not be sy3it reco$$en+ationsK I a'e inclu+e+ te personal notes erein to con'ey $y tougt
process an+ intent – tis too is fair ga$e for criti4ue.
A 3or+ on state +iagra$s>
State +iagra$s 3ere suggeste+ at te last subco$$ittee $eeting as a $eans of
representing te logic. I – along 3it a couple of colleagues ere at &ectel – re'ie3e+tis possibility. )y only pre'ious e6perience 3it tis $eto+ +ates fro$ $y college
+ays, 3en tis 3as taugt as a $eto+ of logic +esign *to be built 3it cips in te lab-.
Pros for tis $eto+(
• Taugt for$ally to engineering gra+s *not sure o3 $any-
• Alrea+y +ocu$ente+ in ISA S55
•8igorous treat$ent of states an+ state transitions *goo+ for a'oi+inguninten+e+ states-
Cons for tis $eto+(
• ;ot use+ $uc in po3er plant applications? I a'e not seen it use+ by utilities,
A: fir$s, or 'en+ors *on te oter an+, te proponents $ust use an+ like it-
• 9unctional block *9&- representation 3oul+ be $ore fa$iliar to $ost po3er
