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 International Symposium on Electrical and Electronics Engineering – ISEEE-2015, Galati, Romania

control, and used to na)igate and edit the logic. Most

ha)e a s"all !lug for connecting )ia R-(:3: or R-(/9= to

a !ersonal co"!uter so that !rogra""ers can use si"!le

7indo*s a!!lications for !rogra""ing instead of #eing

forced to use the tiny LCD and !ush(#utton set for this

 !ur!ose. nli'e regular PLCs that are usually "odular 

and greatly e&!anda#le, the PLRs are usually not "odular 

or e&!anda#le, #ut their !rice can #e t*o orders of "agnitude less than a PLC and they still offer ro#ust

design and deter"inistic e&ecution of the logic.

III. +>ATR>-

 A  Co""unications

Control !anel *ith PLC $grey ele"ents in the center%.The unit consists of se!arate ele"ents, fro" left to right?

 !o*er su!!ly, controller, relay units for in( and out!utThe "ain difference fro" other co"!uters is that PLCsare ar"ored for se)ere conditions $such as dust, "oisture,

heat, cold% and ha)e the facility for e&tensi)e in!ut6out!ut$I6O% arrange"ents. These connect the PLC to sensors andactuators. PLCs read li"it s*itches, analog !rocess

)aria#les $such as te"!erature and !ressure%, and the !ositions of co"!le& !ositioning syste"s. -o"e use"achine )ision.@/ On the actuator side, PLCs o!erateelectric "otors, !neu"atic or hydraulic cylinders,"agnetic relays, solenoids, or analog out!uts. Thein!ut6out!ut arrange"ents "ay #e #uilt into a si"!le

PLC, or the PLC "ay ha)e e&ternal I6O "odules attachedto a co"!uter net*or' that !lugs into the PLC.  PLCs "ay need to interact *ith !eo!le for the !ur!oseof configuration, alar" re!orting or e)eryday control. A

hu"an("achine interface $BMI% is e"!loyed for this !ur!ose. BMIs are also referred to as "an("achineinterfaces $MMIs% and gra!hical user interface $Is%. Asi"!le syste" "ay use #uttons and lights to interact *iththe user. Te&t dis!lays are a)aila#le as *ell as gra!hicaltouch screens. More co"!le& syste"s use !rogra""ingand "onitoring soft*are installed on a co"!uter, *ith the

PLC connected )ia a co""unication interface.PLCs ha)e #uilt in co""unications !orts, usually (!inR-(:3:, #ut o!tionally >IA(/9= or >thernet. Mod#us,EACnet or D+ is usually included as one of theco""unications !rotocols. Other o!tions include )ariousfield#uses such as De)iceNet or Profi#us. Other 

co""unications !rotocols that "ay #e used are listed inthe List of auto"ation !rotocols.Most "odern PLCs can co""unicate o)er a net*or' toso"e other syste", such as a co"!uter running a -CADA$-u!er)isory Control And Data Ac5uisition% syste" or *e# #ro*ser.

PLCs used in larger I6O syste"s "ay ha)e !eer(to(!eer $P:P% co""unication #et*een !rocessors. This allo*sse!arate !arts of a co"!le& !rocess to ha)e indi)idualcontrol *hile allo*ing the su#syste"s to co(ordinate o)er the co""unication lin'. These co""unication lin's arealso often used for BMI de)ices such as 'ey!ads or PC(

ty!e *or'stations.

 !  Progra""ing

PLC !rogra"s are ty!ically *ritten in a s!ecial

a!!lication on a !ersonal co"!uter, then do*nloaded #y adirect(connection ca#le or o)er a net*or' to the PLC. The !rogra" is stored in the PLC either in #attery(#ac'ed(u!RAM or so"e other non()olatile flash "e"ory. Often, a

single PLC can #e !rogra""ed to re!lace thousands of relays.

nder the I>C 23(3 standard, PLCs can #e !rogra""ed using standards(#ased !rogra""inglanguages. A gra!hical !rogra""ing notation called-e5uential +unction Charts is a)aila#le on certain !rogra""a#le controllers. Initially "ost PLCs utili8edLadder Logic Diagra" Progra""ing, a "odel *hich

e"ulated electro"echanical control !anel de)ices $suchas the contact and coils of relays% *hich PLCs re!laced.This "odel re"ains co""on today.I>C 23(3 currently defines fi)e !rogra""inglanguages for !rogra""a#le control syste"s1 function

 #loc' diagra" $+ED%, ladder diagra" $LD%, structuredte&t $-T? si"ilar to the Pascal !rogra""ing language%,instruction list $IL? si"ilar to asse"#ly language% andse5uential function chart $-+C%. These techni5uese"!hasi8e logical organi8ation of o!erations.

"  Digital and analog signals

Digital or discrete signals #eha)e as #inary s*itches,yielding si"!ly an On or Off signal $ or 0, True or +alse,res!ecti)ely%. Push #uttons, li"it s*itches, and !hotoelectric sensors are e&a"!les of de)ices !ro)iding adiscrete signal. Discrete signals are sent using either 

)oltage or current, *here a s!ecific range is designated asOn and another as Off. +or e&a"!le, a PLC "ight use :/< DC I6O, *ith )alues a#o)e :: < DC re!resenting On,)alues #elo* :<DC re!resenting Off, and inter"ediate)alues undefined. Initially, PLCs had only discrete I6O.Analog signals are li'e )olu"e controls, *ith a range of 

)alues #et*een 8ero and full(scale. These are ty!icallyinter!reted as integer )alues $counts% #y the PLC, *ith)arious ranges of accuracy de!ending on the de)ice andthe nu"#er of #its a)aila#le to store the data. As PLCsty!ically use 2(#it signed #inary !rocessors, the integer )alues are li"ited #et*een (3:,29 and F3:,2.

Pressure, te"!erature, flo*, and *eight are often

re!resented #y analog signals. Analog signals can use)oltage or current *ith a "agnitude !ro!ortional to the)alue of the !rocess signal. +or e&a"!le, an analog 0 ( 0< in!ut or /(:0 "A *ould #e con)erted into an integer 

)alue of 0 ( 3:2.Current in!uts are less sensiti)e to electrical noise $i.e.fro" *elders or electric "otor starts% than )oltage in!uts.

 # $%" compared &it' ot'er control systems

PLCs are *ell(ada!ted to a range of auto"ation tas's.These are ty!ically industrial !rocesses in "anufacturing*here the cost of de)elo!ing and "aintaining the

auto"ation syste" is high relati)e to the total cost of theauto"ation, and *here changes to the syste" *ould #ee&!ected during its o!erational life. PLCs contain in!ut

and out!ut de)ices co"!ati#le *ith industrial !ilot

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 International Symposium on Electrical and Electronics Engineering – ISEEE-2015, Galati, Romania

de)ices and controls? little electrical design is re5uired,and the design !ro#le" centers on e&!ressing the desiredse5uence of o!erations. PLC a!!lications are ty!ically

highly custo"i8ed syste"s so the cost of a !ac'aged PLCis lo* co"!ared to the cost of a s!ecific custo"(#uiltcontroller design. On the other hand, in the case of "ass( !roduced goods, custo"i8ed control syste"s are

econo"ic due to the lo*er cost of the co"!onents, *hichcan #e o!ti"ally chosen instead of a ;generic; solution,

and *here the non(recurring engineering charges ares!read o)er thousands or "illions of units.

+or high )olu"e or )ery si"!le fi&ed auto"ation tas's,different techni5ues are used. +or e&a"!le, a consu"er dish*asher  *ould #e controlled #y an electro"echanicalca" ti"er   costing only a fe* dollars in !roduction

5uantities.A  "icrocontroller (#ased design *ould #e a!!ro!riate

*here hundreds or thousands of units *ill #e !roducedand so the de)elo!"ent cost $design of !o*er su!!lies,in!ut6out!ut hard*are and necessary testing and

certification% can #e s!read o)er "any sales, and *herethe end(user *ould not need to alter the control.Auto"oti)e a!!lications are an e&a"!le? "illions of unitsare #uilt each year, and )ery fe* end(users alter the !rogra""ing of these controllers. Bo*e)er, so"es!ecialty )ehicles such as transit #uses econo"ically usePLCs instead of custo"(designed controls, #ecause the

)olu"es are lo* and the de)elo!"ent cost *ould #eunecono"ic.

<ery co"!le& !rocess control, such as used in theche"ical industry, "ay re5uire algorith"s and !erfor"ance #eyond the ca!a#ility of e)en high( !erfor"ance PLCs. <ery high(s!eed or !recision controls

"ay also re5uire custo"i8ed solutions? for e&a"!le,aircraft flight controls. -ingle(#oard co"!uters  usingse"i(custo"i8ed or fully !ro!rietary hard*are "ay #echosen for )ery de"anding control a!!lications *here thehigh de)elo!"ent and "aintenance cost can #e su!!orted.;-oft PLCs; running on des'to!(ty!e co"!uters can

interface *ith industrial I6O hard*are *hile e&ecuting !rogra"s *ithin a )ersion of co""ercial o!eratingsyste"s ada!ted for !rocess control needs.

Progra""a#le controllers are *idely used in "otioncontrol, !ositioning control and tor5ue control. -o"e"anufacturers !roduce "otion control units to #e

integrated *ith PLC so that (code  $in)ol)ing a CNC

"achine% can #e used to instruct "achine "o)e"ents.PLCs "ay include logic for single()aria#le feed#ac' 

analog control loo!, a ;!ro!ortional, integral, deri)ati)e;or ;PID controller ;. A PID loo! could #e used to control

the te"!erature of a "anufacturing !rocess, for e&a"!le.Bistorically PLCs *ere usually configured *ith only afe* analog control loo!s? *here !rocesses re5uiredhundreds or thousands of loo!s, a  distri#uted controlsyste" $DC-% *ould instead #e used. As PLCs ha)e #eco"e "ore !o*erful, the #oundary #et*een DC- and

PLC a!!lications has #eco"e less distinct.PLCs ha)e si"ilar functionality as Re"ote Ter"inal

nits. An RT, ho*e)er, usually does not su!!ort control

algorith"s or control loo!s. As hard*are ra!idly #eco"es"ore !o*erful and chea!er, RTs, PLCs and DC-s areincreasingly #eginning to o)erla! in res!onsi#ilities, and

"any )endors sell RTs *ith PLC(li'e features and )ice

)ersa. The industry has standardi8ed on the I>C 23(3functional #loc' language for creating !rogra"s to run onRTs and PLCs, although nearly all )endors also offer 

 !ro!rietary alternati)es and associated de)elo!"enten)iron"ents.

In recent years ;-afety; PLCs ha)e started to #eco"e !o!ular, either as standalone "odels $Pil8 PNOG Multi,

-ic' etc.% or as functionality and safety(rated hard*areadded to e&isting controller architectures $Allen Eradley

uardlogi&, -ie"ens +(series etc.%. These differ fro"con)entional PLC ty!es as #eing suita#le for use insafety(critical a!!lications for *hich PLCs ha)etraditionally #een su!!le"ented *ith hard(*ired safetyrelays. +or e&a"!le, a -afety PLC "ight #e used tocontrol access to a ro#ot cell *ith tra!!ed('ey access, or 

 !erha!s to "anage the shutdo*n res!onse to ane"ergency sto! on a con)eyor !roduction line. -uchPLCs ty!ically ha)e a restricted regular instruction setaug"ented *ith safety(s!ecific instructions designed tointerface *ith e"ergency sto!s, light screens and so forth.

The fle&i#ility that such syste"s offer has resulted inra!id gro*th of de"and for these controllers.

I<. TRI>N>RATION

Trigeneration, also called CCBP $co"#ined cooling, heatand !o*er%, refers to the si"ultaneous generation of 

electricity, useful heating and useful cooling fro" thesa"e original heat source such as fuel or solar energy.7aste heat insufficient in energy to !roduce electricitythrough "echanical "eans, such as through a stea"tur#ine, contains usa#le energy that is harnessed for ther"al regulation !ur!oses as descri#ed in cogeneration.

Trigeneration differs fro" cogeneration in that so"e of the *aste heat is used for cooling. CCBP syste"s canattain higher efficiencies !er unit fuel than cogenerationor traditional !o*er !lants.

Trigeneration $CCBP% is defined as the e&traction of electrical !o*er and heat fro" fuel *here a !ercentage of 

the heat  #y!roduct is used for cooling. Beating andcooling out!ut "ay o!erate concurrently or #einterchanged #ased need and syste" construction.A !o*er !lant o!erating on the #asis of the Carnot cycle*ill con)ert energy fro" heat to "echanical energy #asedon a te"!erature differential as descri#ed #y the Ran'ine

cycle.@  Mechanical energy is con)erted into electrical

 !o*er #y an electric generator.  7aste heat *hich isinsufficient in energy as in!ut to the electric generator isthen recycled for other !ur!oses such as heating or cooling of li)ing s!ace or industrial facility or as in!ut to

other industrial !rocesses. Cooling is achie)ed through ana#sor!tion chiller or an adsor!tion chiller as the original #y!roduct is heat.

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 International Symposium on Electrical and Electronics Engineering – ISEEE-2015, Galati, Romania

+ig. :. Trigeneration Cycle

Trigeneration $CCBP% is defined as the e&traction of electrical !o*er and heat fro" fuel *here a !ercentage of 

the heat #y!roduct is used for cooling. Beating and

cooling out!ut "ay o!erate concurrently or #einterchanged #ased need and syste" construction.

A !o*er !lant o!erating on the #asis of the Carnotcycle *ill con)ert energy fro" heat to "echanical energy #ased on a te"!erature differential as descri#ed #y the

Ran'ine cycle.@ Mechanical energy is con)erted intoelectrical !o*er #y an electric generator. 7aste heat*hich is insufficient in energy as in!ut to the electricgenerator is then recycled for other !ur!oses such asheating or cooling of li)ing s!ace or industrial facility or as in!ut to other industrial !rocesses. Cooling is achie)ed

through an a#sor!tion chiller or an adsor!tion chiller asthe original #y!roduct is heat.

<. DI-TRIET>D >N>RATION

Trigeneration has its greatest #enefits *hen scaled to fit

 #uildings or co"!le&es of #uildings *here electricity,heating and cooling are !er!etually needed. -uchinstallations include #ut are not li"ited to1 data centers,"anufacturing facilities, uni)ersities, hos!itals, "ilitaryco"!le&es and colleges. Locali8ed trigeneration hasaddition #enefits as descri#ed #y distri#uted generation.

Redundancy of !o*er in "ission critical a!!lications,lo*er !o*er usage costs and the a#ility to sell electrical !o*er #ac' to the local utility are a fe* of the "aHor  #enefits.

Most industrial countries generate the "aHority of their electrical !o*er needs in large centrali8ed facilities *ith

ca!acity for large electrical !o*er out!ut. These !lantsha)e e&cellent econo"ies of scale, #ut usually trans"itelectricity long distances resulting in si8a#le losses,negati)ely affect the en)iron"ent. Large !o*er !lants canuse cogeneration or trigeneration syste"s only *hensufficient need e&ists in i""ediate geogra!hic )icinity for 

an industrial co"!le&, additional !o*er !lant or a city. Ane&a"!le of cogeneration *ith trigeneration a!!licationsin a "aHor city is the Ne* 4or' City stea" syste".

R >+>R>NC>-

@ E.. Bodge, $:00%. JAlternati)e >nergy -yste"s K

A!!lications. Ne* 4or'1 7iley(I>>> Press..

@: ;Trigeneration -yste"s *ith +uel Cells;. Research Pa!er.

Retrie)ed 9 A!ril :0.

@3 Masters, il#ert $:00/%. Rene*a#le and efficient electric !o*er syste"s. Ne* 4or'1 7iley(I>>> Press.

@/ >. A. Parr, Industrial Control Band#oo', Industrial Press Inc.,

I-EN 093309=@= M. A. Laughton, D. . 7arne $ed%, >lectrical >ngineers Reference

 #oo', 2th edition,Ne*nes, :003 Cha!ter 2 Progra""a#le

Controller 4.

@2 ;The father of in)ention1 Dic' Morley loo's #ac' on the /0th

anni)ersary of the PLC;. Manufacturing Auto"ation. :-e!te"#er :009.

@ Bar"s, Toni M. K inner, Russell B. P.>., >nhancing PLC

Perfor"ance *ith <ision -yste"s. 9th Annual >-D6BMI

International Progra""a#le Controllers Conference Proceedings,9, !. 39(3.

@9 Maher, Michael . Real(Ti"e Control and Co""unications. 9th

Annual >-D6-MI International Progra""a#le ControllersConference Proceedings, 9, !. /3(/32.

@ inner, Russell B., P.>. Designing Progra"a#le Controller 

A!!lication Progra"s sing More than One Designer. /th

Annual International Progra""a#le Controllers ConferenceProceedings, 9=, !. (0.

@0 7. Eolton, Progra""a#le Logic Controllers, +ifth >dition,

 Ne*nes, :00 I-EN 9((9=2(=(, Cha!ter

@ eller, 7illia" L r. rafcet, A +unctional Chart for -e5uentialProcesses, /th Annual International Progra""a#le Controllers

Conference Proceedings, 9/, !. (2.

@: regory . McMillan, Douglas M. Considine $ed%,

Process6Industrial Instru"ents and Controls Band#oo' +ifth>dition, Mcra*(Bill, I-EN 0(0(0:=9:( -ection 3

Controllers