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Introduction

The field of industrial com-munications continues to developat an astonishing pace with theresult that the field of automationtechnology is constantly changing.Initially, automation focused almostexclusively on production;however, it has now grown toinclude service and maintenance,warehousing, resource optimizationand the provision of data for MESand ERP systems in addition to theactual task of automation. Fieldbustechnology, which has facilitated

migration from centralized todecentralized automation systemsand supports the use of distributedintelligence, has been the drivingforce behind this development.

Ethernet-based communicationsystems provide a link betweenautomation technology andinformation technology, therebyenabling consistent communicationfrom the field level to the corporatemanagement level.

PROFIBUS and PROFINET arestandardized solutions charac-terized by their unusual ability tocombine total integration with higha high degree of applicationorientation. With its standardprotocol, PROFIBUS encompassesall sub-processes found in factoryand process automation, includingsafety-related communication andmotion control applications. Itthereby provides the ideal basis for ensuring horizontal automationsystem integration. PROFINET

also features a standard protocolwhich, in addition to horizontalcommunication, also supportsvertical communication, therebylinking the field level with thecorporate management level.Therefore, both communicationsystems are able to facilitatenetwork-wide, integrated solutionsthat are optimized for the relevantautomation tasks.

The main reason that PROFIBUSstands out from other industrial

communication systems is becauseit offers such an extraordinarybreadth of applications. Appli-cation-specific requirements havebeen incorporated into applicationprofiles and these have beencombined as a whole to create astandardized and open commu-nication system. This provides thebasis for ensuring extensiveprotection for the investments of both end users and manufacturers.

The application profile for PA

devices (PA profile) plays a keyrole in process automation. Itdefines manufacturer-independentdevice parameters and function-alities for devices used in processengineering, e.g., transmitters,actuators and analyzers. Theprofile provides the foundation for harmonized applications, simplifiedengineering and increasedavailability by means of stan-dardized diagnostic information.


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PROFIBUS PA technology and application, August 20072

Contents

Introduction..................................................................1

Contents ................................................ ......................2

Content ......................................................................2

1. Industrial communication with PROFIBUS ...........3

1.1 Consistent communication with PROFIBUS..3 1.2 PROFIBUS for process automation

(PROFIBUS PA)............................................4 1.3 PROFIBUS for all system components .........5 1.4 Integration of existing systems ......................5

2. Transmission technology and installation.............6

2.1 Power and communication via a singlecable .............................................. ......................6

2.2 Topology .......................................................6

2.3 Connection of DP and PA .............................6 2.4 PROFIBUS PA in hazardous areas...............7 2.5 Bus diagnostics........................................ .....7 2.6 Redundancy............................................... ...8 2.7 Remote I/O....................................................8

3. PROFIBUS communication protocol ....................9

3.1 Device classes ........................................... ...9 3.2 Configuring a PROFIBUS system ...............10 3.3 Cyclic communication..................................11 3.4 Acyclic communication................................11

4. The PA profile.....................................................12

4.1 Structure......................................................12 4.2 Block model and signal flow .......................12 4.3 Device parameters ......................................13

4.4 Operating profile devices............................ 14 4.5 PROFIBUS in safety-related applications... 14 4.6 Functions for device identification and

maintenance support (I&M) ........................ 14 4.7 Device diagnostics...................................... 15

5. Device integration.............................................. 17

5.1 Device master data file (GSD).................... 17 5.2 Electronic device description (EDD)........... 17 5.3 Device type manager (DTM) and field

device tool (FDT) interface ......................... 17

6. System technology ........................................... . 18

6.1 Paradigm shift in process automation......... 18 6.2 PROFINET in automation technology......... 18

7. Conformity and certification ............................... 20

7.1 Quality control through certification ............ 20 7.2 PA device certification ................................ 20

8. User benefits ..................................................... 21

9. PI PROFIBUS & PROFINET International...... 22

9.1 Responsibilities of PI .................................. 22 9.2 Technological development........................ 22 9.3 Technical support ....................................... 22 9.4 Certification ................................................ 22 9.5 Training ...................................................... 22 9.6 The Internet: An information hub ................ 22

9.7

Further reading........................................... 22

Index ................................................. .................. 23

Content

This document describes theessential aspects of PROFIBUSused in process automation andtakes into account the level of technology available at thebeginning of 2007. Its objective isto provide a comprehensivedescription of PROFIBUS andPROFINET, the worlds leadingfieldbus systems, without enteringinto specific details.

This brochure not only offerssufficient information to readerswith a basic knowledge who areinterested in obtaining an overview,but it also introduces experts tomore extensive specializedliterature. In this context, we shouldlike to point out that although every

care has been taken in the draftingof this brochure, only the official PI(PROFIBUS & PROFINETInternational) documents are to beconsidered definitive and binding.

Chapter 1 provides anintroduction to PROFIBUS and itsuse in process automation.

Chapters 2 to 4 deal with thecore aspects of PROFIBUS PA.

Chapter 5 offers a brief outline of engineering.

Chapter 6 deals with theintegration of existing structuresinto PROFIBUS PA and thetransition to PROFINET.

Chapter 7 outlines the testprocedures required for certification.

Chapter 8 explains the advantagesof using PROFIBUS PA.

Chapter 9 concludes thedocument with information about PIand its range of products andservices.

This chapter is followed by theindex.


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PROFIBUS PA technology and application, August 2007 3

1. Industrialcommunication withPROFIBUS

Since the cost-pressure associated

with the operation of productionfacilities is so high, achievingmaximum system availability andminimum total cost of ownershiphave high priorities. Therefore,holistic approaches not only takeinto account the procurement andmaintenance costs associated withsystem components but also thecosts of optimizing process control.In process engineering, idealprocess control should supportmonitoring and controlling of aprocess in the most cost-effectiveway given the requirements of theprocess and system. This requiresextensive information about theprocess and the system. Today,this information is made availableby intelligent field devices andcommunicated via fieldbuses. Theproblem-free and consistentavailability of all necessary data isan important prerequisite for optimized processes.

1.1 Consistent

communication withPROFIBUS

Operators of process engineeringsystems find themselves facing awhole range of very differenttechnical challenges and arelooking to achieve standardizationwherever possible. Accordingly,Integration instead of interfacesand One technology instead of multiple technologies are therequirements to be met byfieldbuses to support suchstandardization. PROFIBUS is thehomogeneous technology meetingthese requirements, therebygenerating significant added valuethroughout the life cycle of asystem.

PROFIBUS is the fieldbus-basedautomation standard from PI(PROFIBUS & PROFINET Interna-tional). It offers comprehensivesolutions encompassing actualcommunication, applicationprofiles, system integration andengineering. The standard for

PROFINET, an Ethernet-basedautomation fieldbus, was recentlyreleased by PI. PROFIBUS andPROFINET use identical profiles,thereby creating investment

security and investment protectionfor both the users andmanufacturers of these tech-nologies. Both PROFIBUS andPROFINET are characterized bytheir support for both factory andprocess automation and, in

particular, by their ability tofacilitate implementation of hybridapplications.

PROFIBUS consistency is basedon the standardized PROFIBUSDP communication protocol. Itsupports a wide variety of applications in factory automationand process automation as well asmotion control and safety-relatedtasks, thus facilitating planning,assembly and service. Additionally,training, documentation andmaintenance are only required tosupport a single technology.

Users with hybrid automationapplications (see Chapter 1.3) inparticular benefit from the uniqueability of PROFIBUS technology toseamlessly integrate process-oriented and factory-oriented tasks.This is of particular relevance in thepharmaceutical and foodstuffsindustries.

The modular structureof PROFIBUS

PROFIBUS technology has amodular structure, comprised of mutually compatible technologycomponents which can be selectedand combined in accordance withapplication requirements in muchthe same way as a modular system(Figure 1).

At the heart of the system is thePROFIBUS DP protocol, which isidentical for all applications (seeChapter 3). Various datatransmission media are available:RS485 for standard applications,RS485-IS for areas with explosion

protection, MBP for intrinsically-safe transmission with devicepower supply via the bus, fiber optics, radio-based transmission(see Chapter 2), infrared- andlaser-based transmission, sliprings, etc.

In order to ensure theinteroperability of devices bydifferent manufacturers that is sovital to a wide range of applicationsand to transmit extensiveinformation from complex devicesin accordance with definedstandards, application profileshave been specified for PROFIBUS. These profiles specifyapplication-typical device featureswhich profile devices must exhibitas a mandatory requirement.These profile features might spanmultiple device classes, e.g.,safety-relevant behavior, or features that are specific to aparticular device class, e.g., to beexhibited by process devices or drives. Devices with differentprofiles can operate on the samebus system. Very simple devices,e.g., decentralized binary I/Odevices, do not usually useapplication profiles. PI hasspecified the profile for PA devices(Profile for Process ControlDevices or PA profile) for processautomation (see Chapter 4).

Figure 1: The PROFIBUS modular system


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1.2 PROFIBUS for process automation(PROFIBUS PA)

Defined in general terms,

PROFIBUS PA designates aspecific selection of PROFIBUStechnology components (modular system components) meeting theparticular requirements of processautomation. PROFIBUS PAencompasses all technologycomponents used to connectintelligent field devices tocontrollers, control systems andengineering stations and offeringideal solutions for processautomation.

MBP (Manchester-encoded, BusPowered) technology, a 2-wiretechnology which combines thefunctions of data transmission andpower supply, is usually used onPROFIBUS PA. MBP-IS (IS =intrinsically safe) is available for use in hazardous areas. Withshort-circuit protection and power limitation, the installation tech-nology supports the explosion-protected operation of field devicesin Zones 0, 1 and 2 and/or ClassI/Div.1 and Class I/Div.

The simple topology of PROFIBUSPA pays off as early as theplanning phase: The scope of documentation can be reduced byup to 90% when compared to a 4-20 mA installation. During thecommissioning phase, loop checkscan be completed much morequickly, significantly reducing thetotal time line from planning tocommissioning. The flexibility of PROFIBUS installation also makesadding more devices, retrofitting or replacing devices easier onceoperation is underway. When add-ons or expansions affecting older systems are required, 4-20 mAdevices or HART devices can be

integrated into PROFIBUSinstallations with ease. PROFIBUSPA installations have shownevidence of very high availabilityeven in the harsh conditions of day-to-day operations. However,the use of diagnostic tools, e.g., tomonitor voltage levels and jitter anddetect evidence of wear at an earlystage (see Chapter 2.5), isrecommended duringcommissioning and periodicallyonce a system is in operation.Redundancy solutions for PROFIBUS PA to increase systemavailability (see Chapter 2.6) are

available for applications with highavailability requirements.

The PA profile classifies thedevices used in processautomation as transmitters,actuators, devices for digital inputsand outputs, or analyzers. For eachdevice class, the profile specifiesthe associated functions andparameters which can be used toadapt the device functions to theindividual application and processconditions. The specification isbased on function blocks andparameters types are classified asinput, output and internal. Theprofile also specifies how theservices of the PROFIBUScommunication protocol are used.For example, process dataexchanged cyclically is based on astandard format for all processautomation devices. In addition tothe measured value and/or manipulated value, this format alsofeatures a status byte providinginformation about the quality of thevalue and possible limit violations.

The device functionality specified inthe PA profile facilitates standardhandling of process devices not

only from the point of view of thecontroller but also from theperspective of asset management.Furthermore, the interoperability of like devices from differentmanufacturers facilitates theexchange of devices on the bus.The best way to appreciate thewide and varied range of PAdevices, control systems and assetmanagement systems available onthe market is to take a look at theOnline product guide atwww.profibus.com.

The diagnostics concept defined in

the PA profile also provides thebackbone for comprehensive assetmanagement. PROFIBUS PA canutilize these concepts to tap intothe enormous potential for cuttingcosts, since necessary mainte-nance operations can be plannedin line with the production scheduleand/or scheduled downtimes.

PROFIBUS is internationallystandardized in IEC 61158/61784and is the most successful andproven fieldbus technology on themarket. More than 20 millioninstalled PROFIBUS devices makePROFIBUS the most successfulcommunication standard in theworld. Of this total, over 3.5 millionare in use in the process industryand more than 700,000 devicesconform to the PA profile andutilize MBP communication. Usersfrom all sectors of industry can usePROFIBUS to significantly improvetheir production processes anddramatically reduce the total cost of ownership. Supporting PROFIBUS,PI is an organization with

representation at national levels,with competence centers and testlaboratories in countries all over the world (see Chapter 7).


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1.3 PROFIBUS for allsystem components

Many production facilities runprocess control procedures that are

characterized by continuousmeasurement and control pro-cesses alongside sequences thatrely heavily on manufacturingtechnology that is very much basedon discrete process stages. In suchsystems, the overall processcomprises three stages: inboundlogistics (pre-production), produc-tion itself and outbound logistics(post-production). Inbound logisticsincludes processes such ashandling of incoming goods,warehousing and supply of materials. Outbound logisticsincludes the packaging andshipping of finished products, for example.

Some typical examples are:

In the pharmaceuticalsindustry, the manufacture of medicines is a process controlprocedure, but packaging,e.g., of tablets, is a discretemanufacturing procedureusing complex packagingmachines.

In a brewery, the processcontrol tasks typical of thebrewhouse and fermentationcellar are followed by discretemanufacturing tasks. Suchtasks might include bottlecleaning and filling as well asthe stacking of crates for delivery, a task for whichrobots may be used.

In vehicle construction, thepaint shop, with its processcontrol requirements, is part of a production chain that isotherwise typical of discretemanufacturing.

The use of PROFIBUS enables allareas within a production facility tobe automated with a singletechnology. Production facilitieswith heterogeneous fieldbus

solutions for different areas andtheir associated additionalexpenditures for engineering, datastorage and documentation, andthe additional costs involved intraining, have become a thing of the past.

For comprehensive planning andoptimization, the consistency of acommunication system at the fieldlevel should also take into accountthe capability for vertical integrationinto the corporate managementlevel utilizing, for example,Ethernet-based communicationstechnology. Network transitionsfrom PROFIBUS to PROFINETenable PROFIBUS systems to belinked seamlessly to PROFINETand thus into the corporationmanagement level (see Chapter 6).

1.4 Integration of existing systems

These days, a significant share of the investments made in process

engineering is spent on expansionand modernization. Many projectshave proved just how suitablePROFIBUS is for such situations.The Remote I/O and HART onPROFIBUS profiles support theintegration of installed 4-20 mAdevices into a PROFIBUScommunication system withoutrequiring changes to be made tocables, thereby allowing maximumbenefit to be derived from theadvantages of a fieldbus system(see Chapters 2.7 and 6.1).

InboundLogistics

OutboundLogistics

ProductionProcesses

PROFIBUS PROFIBUSPROFIBUS

Identifying

Conveying

Storing Storing

Packing

Filling

Conveying

Separating

Heating

Mixing

Drying

Checking

InboundLogistics

OutboundLogistics

ProductionProcesses

PROFIBUS PROFIBUSPROFIBUS

Identifying

Conveying

Storing Storing

Packing

Filling

Conveying

Separating

Heating

Mixing

Drying

Checking

Figure 2: Integrated PROFIBUS solution in a production facility


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2. Transmissiontechnology andinstallation

2.1 Power andcommunication viaa single cable

Like conventional 4-20 mA or HART communication technol-ogies, fieldbus technology supportsthe simultaneous transmission of power and communication data viaa single cable, even in potentiallyexplosive atmospheres. Further-more, with wiring overheadssignificantly reduced, it meets therequirements for simpler and safer installation and boasts all thebenefits of digital transmission.

IEC 61158-2 defines MBP(Manchester-encoded, BusPowered)

,as a transmission

technology satisfying allrequirements of and developedspecifically for the needs of process automation. Thistransmission technology makes itpossible to supply power to theconnected devices directly via thebus medium. MBP is characterizedby the following features:

Transfer rate: 31.25 kbps Transmission technology: Half-

duplex, synchronous, self-clocking, with Manchester biphase L encoding

CRC (cyclic redundancycheck)

Data security: Preamble, fail-safe start-end delimiters

Cable: Shielded, twisted pair line (type A or type B)

Topology: Line and treetopology with termination;combined topology possible

Number of stations: Up to 32stations per segment

Ignition protection: Severalmethodologies andtechnologies

Explosion protection isimplemented via power limiting of the incoming bus supply as well asinstallation components in the field.Live maintenance on field devicesduring plant operation is madepossible, for example, by means of intrinsically safe explosionprotection. The easiest way toverify intrinsic safety of a segmentis to use the FISCO model. In this

case, since all components usedcomply with FISCO standardssimple comparisons of power voltage and current eliminatefurther calculations (see Chapter 2.4).

2.2 Topology

PROFIBUS PA offers quite flexibleinstallation concepts which, thanksto the advanced installationtechnologies available on themarket, can lead to incrediblyrobust systems. In principle, alltopologies are supported.However, in practice, the trunk &spur topology (Figure 3) hasestablished itself as the de factostandard due to the fact that it is so

clear and easy to understand andmaintain. The total length of asegment in the most ideal situationmust not exceed 1,900 meters.Transmission conditions for PROFIBUS PA can be optimizedby using type A cable consisting of a single shielded, twisted pair. Allsegments must be terminatedcorrectly with terminating resistors(T in Figure 3). Theseterminations are very important for reliable operation due to their effecton signal quality.

2.3 Connection of DP and PA

The connection between aPROFIBUS DP and a PROFIBUSPA segment is accomplished usingsegment couplers or DP/PA links.Essentially, both componentsperform the following tasks:

Converts the asynchronousRS485 bus physics into thesynchronous MBP bus physics

Supplies voltage for the PAsegment and limits thesegment current supply

Decouples the transmissionspeeds of RS485 and MBPbus physics

Optional: Provides isolationand power limitation for hazardous areas

An essential feature of segmentcouplers is the ease with which theentire network can be configured.All PA devices are visible byaddress (transparent solution) onthe DP side. The couplers

themselves do not need to beconfigured.

The DP/PA link appears on the DPbus as a separate modular slavedevice with the connected PAdevices appearing as plug-inmodules. An essential feature of the DP/PA link is the provision of atotally isolated address space for its connected PA devices (non-transparent solution). It has to beconfigured separately and restrictsthe total amount of data which canbe transferred to and from the

connected PA devices to 244bytes. The cyclic data from all theconnected PA devices iscompressed into a single DPtelegram.

The faster DP segment enables anumber of PA segments to beintegrated into a DP network viasegment couplers or links.

T

T

Field devices

Fieldbus Distribution Terminator

Segment Coupler/Linkand Power Supply

PROFIBUS DP

PROFIBUS PA

Trunk

Spur

T

T

Field devices

Fieldbus Distribution Terminator


PROFIBUS DP

PROFIBUS PA

Trunk

Spur

Figure 3: Trunk & spur topology


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2.4 PROFIBUS PA

in hazardous areas

Significant care must be takenwhen designing segments if PROFIBUS PA is to be used inhazardous areas. The FISCO(Fieldbus Intrinsically SafeConcept) model referred to abovecan make planning, installing andexpanding PROFIBUS networks inhazardous areas significantlyeasier. The model is based on theconcept that a network segmentcan be considered intrinsically safe(with no separate intrinsic safetycalculation required) if the voltage,current, power, inductance andcapacitance values of the relevantcomponents (cable, segment

couplers, bus terminators) arewithin the boundaries of prescribedFISCO limits and all field devicesare FISCO certified.

The FISCO model is based on thefollowing principles:

Each segment only has onepower source (the supply unit).

Each field device consumes aconstant basic current of atleast 10 mA.

The field devices always actas passive current sinks.Even when a station istransmitting, no power is fedinto the bus.

There is a passive lineterminator at each end of themain bus line.

Line, tree and star topologynetworks are possible.

Components and instrumentationby various manufacturers can beoperated on the same segmentprovided that all of them meet the

requirements described. Intrinsicsafety is considered proven if allstations on an electrical circuithave been certified in accordancewith FISCO as defined in IEC60079-27. A simple comparison of current, voltage and power of thesupply and the field device isrequired to validate explosionprotection. For Zone 2, energy canbe limited to Ex nL (non-incendive).Both concepts have been includedin the revised version of IEC60079-27. (Entity is another intrinsically safe model which isused in the USA and regions withclose ties to the United States.)

Power limiting in potentiallyexplosive atmospheres cansignificantly restrict cable lengthsand the number of configurablefield devices per segment. Thehigh-power trunk conceptovercomes this obstacle by means

of the spatial distribution of the"fieldbus power supply" and"protection via intrinsic safety"functionalities. This concept isbased on the typical practice thatservice operations and/or deviceexpansions are usually performedon field devices and their connecting cables (spurs) and onlyrarely on the main trunk linebetween the control room and the

distributors in the field. Based onthis typical practice, it is thereforepossible to split the fieldbusinstallation into two different typesof explosion protection.

The trunk between the safe areaand the fieldbus distributors isdesigned with Ex-e (increased

safety) and, unlike Ex-i (intrinsicsafety), imposes virtually norestrictions in terms of power limitations. The "fieldbus barriers",which support the connection of upto four field devices, then act asdistributors mounted in Zone 1.Connecting several fieldbusbarriers in series enables thepossible cable length and number of stations per segment to bemultiplied many times over incomparison with either the Entity or the FISCO model. Here too, theFISCO or Entity concept is appliedto each spur to verify Ex-safety;each output is verified separately,with the fieldbus barrier as power source and the field device as sink.

Since the incoming power suppliedvia the Ex-e-protected trunk is sohigh, this concept is also referredto as the high-power trunkconcept.

2.5 Bus diagnostics

Fieldbus diagnostics enables thephysical layer to be measured on asegment- and field device-specificbasis. Bus diagnostics consid-erably simplifies commissioning.Once installation is complete, theloop check can be carried out atthe touch of a button (subject toappropriate software

support). Extensive expertknowledge about waveforms andpossible causes are no longer always required for commissioning.

Although no evidence of artificialageing was detected duringlaboratory testing, there are other substantive reasons for permanent

monitoring. The most commoncausecauses of changes on afieldbus areis authorized or unauthorized interventions in thecontext of maintenance or assembly operations. Allparameters affecting transmissionquality are monitored usingdiagnostics tools to ensure thatthey remain within permissiblelimits.

By integrating diagnostics into thepower supply technology, itbecomes possible to monitor systems permanently rather thanjust sporadically, thereby facilitatingthe identification of errors whichmight otherwise go unnoticed

T

T

Field devices

Terminator


PROFIBUS DP

PROFIBUS PA

Safe Area

High Power Supply, non-Ex

Spur, energylimited

Trunk, withoutenergy limitation

Smart installation technology

Ex Area

T

T

Field devices

Terminator


PROFIBUS DP

PROFIBUS PA

Safe Area

High Power Supply, non-Ex

Spur, energylimited

Trunk, withoutenergy limitation

Smart installation technology

Ex Area

Figure 4: Fieldbus barriers with High Power Trunk


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during operation. This also makesit possible to detect changes on thephysical layer and rectify errorswhich might cause the bus to fail.Bus diagnostics also makestroubleshooting much easier, asmaintenance personnel are

provided with detailed information,often with content in plain text,about possible errors.

(Note: Chapter 4.4 deals withdiagnostics relating to the state of field devices.)

2.6 Redundancy

Redundant systems are generallyused for applications requiringincreased availability, e.g.,

continuous processes. In suchsystems, both the master and thecommunication system (media andsegment couplers) are designedwith redundancy. There are variousredundancy concepts: Master redundancy: The

control system/controller isdesigned with redundancy,e.g., flying redundancy (Figure5, right).

Media redundancy: The cableroutes are designed withredundancy.

Segment coupler redundancy:The segment couplers aredesigned with redundancy(Figure 5, left). If one DP-PAgateway fails, the other willtake over its functionseamlessly. The master isunaware of the switchover andno frames are lost.

Ring redundancy: In additionto the redundant design of theDP-PA couplers, the ringstructure also enables mediaredundancy to be achieved onthe PA side (Figure 6).

Slave redundancy: The fielddevices/PROFIBUS interfacein the field device aredesigned with redundancy.

Concepts for slave redundancy aredescribed in the PROFIBUSspecification titled Slave Redun-dancy. Field devices designedwith redundancy must negotiatebetween themselves which is to actas the primary station and which asthe secondary station. Manu-facturer-specific solutions areavailable for transmission mediaand master redundancy.

2.7 Remote I/O

PROFIBUS PA devices can beused in a wide range of applications. Some devices are,able to transmit multiple measuredvalues, thereby reducing the needfor additional instruments. They are

supplied with power via the bus,thus helping to reduce wiringoverhead. Digital transmissionhelps to increase system accuracyand avoids the potential scalingerrors common with 420 mAtechnology by differentiatingbetween the settings in the controlsystem and those in the fielddevice. Devices can beparameterized via the bus andtypically have a reduced footprint.

However, there are some process

signals and/or devices which donot have a direct PA connectionand for which the costs associatedwith a fieldbus interface

bear no relationship to the lowoverall costs of the device. In suchcases, when existing systems arebeing modernized, use is made of existing equipment wherever possible and installed field devicescontinue to be used. Remote I/Otechnology provides a means of integrating devices of this type into

PROFIBUS PA installations.Analog and binary input and outputsignals are collected by a remoteI/O device that is in turn connectedto the control system via thefieldbus. Where HART-compatibleremote I/O are concerned,parameter data is transmitted viathe bus to the remote I/O device,where it is converted into HARTcommands on the appropriate inputor output channel. In this way, thefield devices can be configuredfrom the control system or by useof a parameterization tool viaPROFIBUS and the downstreamHART communication system.

Host Host

DP-Master DP-Master

Flying Redundancy combined withSegment Coupler Redundancy

Segment coupler

Segment coupler

Host

DP-Master

Segment coupler redundancywith single host

Segment coupler

Segment coupler

PROFIBUS PA

PROFIBUS DP

PROFIBUS PA

PROFIBUSD

P

Host Host

DP-Master DP-Master

Flying Redundancy combined withSegment Coupler Redundancy

Segment coupler

Segment coupler

Host

DP-Master

Segment coupler redundancywith single host

Segment coupler

Segment coupler

PROFIBUS PA

PROFIBUS DP

PROFIBUS PA

PROFIBUSD

P

Figure 5: Segment coupler redundancy (left) and flying redundancy (right)

PROFIBUS PA

DP/PA Link(redundant)

PROFIBUS DP

Active junction boxes

PROFIBUS PA

DP/PA Link(redundant)

PROFIBUS DP

Active junction boxes

Figure 6: PA ring redundancy


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3. PROFIBUScommunicationprotocol

PROFIBUS devices communicate

using the standardized PROFIBUSDP (Decentralized Periphery)communication profile whichdefines the rules governingcommunication. At the heart of thecommunication profile is what isknown as the master/slaveconcept, whereby a master (activecommunication peer) polls theassociated slaves (passivecommunication peers) cyclically.When polled, a slave will react bysending a response frame to thepolling master. A request frame

contains the output data, e.g.,setpoint speed of a drive, and theassociated response framecontains the input data, e.g., thelatest measured value from asensor. In one bus cycle, themaster polls, e.g., exchanges I/Odata with, all associated slaves.This polling cycle is repeated asfast as possible.

In parallel with this type of communication, which is describedas cyclic and supports the regular exchange of input and output databetween a master and its slaves,parameter data, e.g., devicesettings, can also be transmittedvia PROFIBUS. This action isinitiated by the master (typicallyunder user program control)between I/O cycles to read and/or write slave parameter data. Thistype of communication is referredto as acyclic communication.

There can be more than onemaster on a PROFIBUS system. Insuch systems, access rights are

passed from one master to the next(token passing).

In order to meet the specificrequirements of the various fieldsof application in the best wayspossible, the PROFIBUScommunication system has beenexpanded beyond its basicfunctionality to include a number of additional levels supporting specialfunctions. There are currently threesuch protocol levels: DP-V0, DP-V1 and DP-V2.

The major features of the three areas follows:

DP-V0 supports the basicfunctionality of the PROFIBUSprotocol. In particular, thisincludes cyclic I/Ocommunication and diagnosticreporting.

DP-V1 adds optional functionsfor acyclic communication andalarm handling (enhancementsto diagnostic reporting) to thePROFIBUS protocol.

DP-V2 adds optional functionsto the PROFIBUS protocolwhich are needed particularlyin the field of drive control.

These include functions for producer-consumer communication between slavedevices, time synchronizationand time stamping.

Field devices for processautomation are typically slavedevices which support the basicfunction of the PROFIBUScommunication protocol (DP-V0)and are also capable of acycliccommunication for the reading/writing of device parameters (DP-

V1).

3.1 Device classes

PROFIBUS devices can becategorized into three deviceclasses:

Class 1 PROFIBUS DPmaster A class 1 DP master (DPM1) is amaster which uses cycliccommunication to exchangeprocess data with its associatedslaves.

Class 1 masters are usuallyintegrated into a programmablelogic controller or form part of theautomation station on a process

control system.

Class 2 PROFIBUS DPmaster A class 2 DP master (DPM2) wasoriginally defined as a master to beused as a tool in the context of PROFIBUS device and systemcommissioning. In the course of theDP-V1 and DP-V2 functionalexpansions, a DPM2 has beenmore specifically defined as amaster which can be used to setdevice parameters via acycliccommunication over what is knownas the MS2 channel.

Cycle:

DP Slave 1

PROFIBUS DP

Master Class 1

PROFIBUS DP

Master Class 2

DP Slave 2 DP Slave 3

Token

Slave 1 Slave 3Slave 2 Slave 3

Cyclic Access of Master 1 Acyclic Accessof Master 2

.....Cycle:

DP Slave 1

PROFIBUS DP

Master Class 1

PROFIBUS DP

Master Class 2

DP Slave 2 DP Slave 3

Token

Slave 1 Slave 3Slave 2 Slave 3

Cyclic Access of Master 1 Acyclic Accessof Master 2

.....

Figure 7: Cyclic and acyclic communication on DP-V1


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Class 2 masters are usually part of an engineering station used for device configuration. A DPM2 doesnot have to be permanentlyconnected to the bus system.

PROFIBUS slaveA PROFIBUS slave is a passivecommunication peer which reactsto polling by the master by sendinga response frame. Devices in thisclass are usually field devices(remote I/O, drive, valve,transducer, analyzer) whichacquire process variables or play apart in the process by means of manipulated variables.

There are two different types of slave devices, compact devices

and modular devices. A modular device comprises a head stationcontaining the fieldbus interfaceand a number of slots into whichvarious modules can be inserted.By combining different modules,modular slaves can be configuredto satisfy the specific I/Orequirements of the user. Compactdevices have a fixed I/Oconfiguration comparable to amodular device with onepermanently installed module.

Slave devices for processautomation may have discrete or word I/O. The majority of suchdevices provide measured valuesas input(s), with some being single-variable and some being multi-variable devices. Multi-variabledevices can be thought of asmodular devices on which, rather than being physically present, theindividual modules simply exist inthe device software (virtualmodules). Access to the associatedinput and output data, e.g.,measured values, setpoints, etc.,

are activated when cycliccommunication is established. Theprocess I/O data (virtual modules)associated with a processautomation slave device arespecified in the profile for PAdevices.

Frequently, PROFIBUS master devices support the functions of both a DPM1 and a DPM2.Similarly, there are also automationdevices which are able to operateas both masters and slaves. Inpractice, it is not always possible tounequivocally categorize physical

devices into the functional classesoutlined above.

3.2 Configuring aPROFIBUS system

When a PROFIBUS system isconfigured, slaves with which themaster is to communicate cyclicallyare assigned to a class 1PROFIBUS DP master. During theconfiguration process, master andslave addresses are assigned, thebus parameters are defined, thetypes and numbers of modules (inthe case of modular slaves) arespecified, user-selectable param-eter choices are made, etc.

PROFIBUS protocol message

frames have a source and targetaddress by means of which thesender and receiver can beuniquely identified. The PROFIBUSdevice address range runs from 0to 126 and, within a singlePROFIBUS network, deviceaddresses can only be assignedonce. Broadcast address 127 canbe used to address multiple slavessimultaneously. The deviceaddress can be set using thephysical address switches on thedevice or the PROFIBUS messagefor address setting, e.g., sent fromthe configuration tool. The physicaladdress assigned to the devicemust match the address assignedto the device in the configurationsetup. If a DP/PA link is being usedas the coupler, it has a slaveaddress on the RS485 side and amaster address on the MBP side.Addresses on the RS485 side areindependent of those on the MBPside, i.e., the two sides haveseparate address spaces. Rather than being limited by the number of available addresses, the scope of aPROFIBUS PA system is usuallyrestricted by physical propertiessuch as cable lengths and devicecurrent consumption (see Chapter 2).

Major bus parameters are transfer rate, watchdog time, slot time, andtarget token rotation time. AsPROFIBUS masters usually havean RS485 interface, the transfer rate can be set to a value between9.6 kbps and 12 Mbps. Althoughmost modern couplers can operateat any transfer rate on the RS485side, some older models only sup-

ported a fixed rate of 93.75 kbpsand/or 45.45 kbps and sometimesrequired that the bus parametersbe modified to manufacturer-defined values. The slave deviceswatchdog is used in monitoringcyclic communication and must be

set significantly higher than thetime required for one bus cycle. If aslave does not receive a requestframe for a period of time longer than the set watchdog time, it willrevert to its initial, power-up stateand cyclic communication will haveto be reestablished. If the master does not receive a valid responsefrom a slave within the configurableslot time, it will resend the requestframe as many times as it can upto the maximum retry limit. Thetarget rotation time is the

configuration tool-calculated timefor the token to traverse the tokenring. It should be set to the samevalue on all masters in a multi-master system. A master calculates its own token holdingtime by taking the differencebetween the target token rotationtime and the measured rotationtime.

In the case of modular slaves, theindividual slave modules must beconfigured. The configuredmodules should match slot-for-slotthose which are physically presentin the device. In the case of PROFIBUS PA slaves, the slavewill have a default, power-upconfiguration of virtual modules.The types and numbers of virtualmodules are either profile- or manufacturer-specified dependingupon whether the device isoperating in profile- or manufacturer-identifier mode. Theconfigured modules determine thesize and format of any I/O dataexchanged during cyclic

communication.A configuration tool (usuallyprovided by the manufacturer of the class 1 PROFIBUS DP master)is used for building a busdescription. The configuration tooltakes the device-specific prop-erties, e.g., the transfer rates sup-ported or the available modules,from the device master file (GSD)of a slave device. This is an ASCIIfile describing the communication-specific and I/O properties of aPROFIBUS device that is providedby the device manufacturer.


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3.3 Cycliccommunication

Once the configuration (busdescription) has been loaded intothe class 1 master with the help of the configuration tool, the master

establishes cyclic communicationwith the specified slave devices viathe MS0 channel. During thisphase, the slave adopts a two-stage approach to checking theconfiguration data received fromthe master.

First, the parameters set in theconfiguration, e.g., watchdog timeand PROFIBUS ID number, aretransferred to the slave andchecked. The ID number is uniquefor each device type and isassigned by PI (PROFIBUS &PROFINET International). Cycliccommunication can only takeplace if the ID number from theconfiguration matches the IDnumber stored in the slave.

Next, the description of theconfigured I/O modules istransferred to the slave andchecked. Cyclic communicationcan only be established if themodules which are physicallypresent match those specified inthe configuration or, in the case of

PA devices, if the device canassign virtual modules to match theconfiguration received.

Successful establishment of I/Odata communication is then verifiedvia the requested diagnostics data.Invalid parameter or configurationdata is indicated by correspondingerror indicators in the standardPROFIBUS diagnostics. If both theparameter and configuration data

are valid, the master will initiatecyclic I/O data communication withthe slave device.

PROFIBUS diagnostics comprisesboth the required standarddiagnostics and the optional

extended diagnostics. The latter contains device-specific diagnosticdata, for example, analog over-voltage, operating temperatureexceeded, output short circuit, etc.Any changes in device-specificdiagnostics data will be indicatedby a flag in the response frameduring cyclic communication. Themaster will respond accordingly inthe next bus cycle by polling for thediagnostic data instead of theprocess data.

A DP slave can only enter intocyclic data exchange with oneDPM1. This ensures that a slavecan only receive output data fromone master, thereby avoidinginconsistent output control.

3.4 Acycliccommunication

A key part of the acyclic dataexchange process is the writing or reading of device parameters ondemand by a master. These deviceparameters can be used to tailor the configuration of a field device toexactly match the applicationrequirements. Two different chan-nels, MS1 and MS2, exist for acyclic communication. An acycliccommunication link between amaster and a slave (MS1 link for short) can only be established if cyclic data exchange is takingplace between that master and theslave.

Since a slave can exchange cyclicI/O data with only one master at atime, it follows that a slave can onlyhave one MS1 link. If supported bythe device (indicated in the GSDfile), the MS1 link is establishedwhen cyclic communication is

established with the device.

It is possible for a slave to have anMS2 link with a number of masterssimultaneously. Each MS2connection must be establishedexplicitly by a master. Each MS2connection has its own timemonitoring mechanism and will beclosed if it is not used for a setperiod of time. Unlike cycliccommunication, a configurationbased on the device master file isnot required for acycliccommunication. Typically, theaddress of the device is all that isneeded to establish an MS2 linkfrom the master.

Device parameters are addressedin a slave device by means of slotnumber and index. The virtual or physical slot is identified by a slotnumber (0 254) on a modular device. On PA devices a slotaddresses a function block (seeChapter 4). An index (0 to 254)into the slot addresses a parameter of the function block.

Devices conforming to PA profile3.0 and higher must support anMS2 channel, although the MS1channel is optional. In practice,very few PA profile devicesimplement an MS1 channel.Therefore, the MS2 channel isused almost universally for acyclicdata transmission in processautomation devices.


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4. The PA profile

The PROFIBUS profile for PAdevices standardizes the corefunctionalities of devices in processautomation. Process devices arecategorized into individual deviceclasses with functionality asdescribed in detail by the profile.Users benefit from the commonmanufacturer-independent corefunctionality of the devices in adevice class due to the identicalway in which those devicesoperate. A generic, profile-specificdevice driver (see Chapter 5) canbe used to integrate a device of this type into a control/assetmanagement system and operate itwithin the functional scope

specified in the profile, i.e., inprofile mode, without the need for manufacturer-specific drivers.

4.1 Structure

The PA profile is structuredaccording to the functionalclassification of the processautomation devices.

Part 1 contains the basicspecifications. In this part, thedevice model illustrated below isbased on function blocks. Thestandard parameters available ineach block are defined and thebasic functions, e.g., saving andtransfer of a linearization table, arespecified. Part 1 also containstables with codes for manufacturer names, technical units of measurement, etc.

Part 2 describes the PROFIBUS-specific properties of a processdevice and the relationshipbetween the profile and the

PROFIBUS communication proto-col. Specifications to be made bythe manufacturer from the point of view of the PROFIBUS protocol areindicated here for the benefit of process device uniformity. Theseinclude, for example, specific

configuration bytes for each deviceclass. This ensures that in thecontext of manufacturer-independent cyclic I/O dataexchange, PA devices in the sameclass communicate using the samedata formats. The data formatspecified for transmitters andactuators consists of five bytes.The first four bytes contain themeasured or manipulated value asa 32-bit floating point number andthe fifth byte, the status byte,provides information about the

quality of the measured value. Part2 also contains specificationsregarding uniform support of anyoptional PROFIBUS commu-nication services, a specification of the encoding of device-specificdiagnostic information and a list of the communication services whichmust be used to transfer theparameters specified in theprotocol.

Parts 3 to 8, also referred to asdata sheets, provide very detailedspecifications for the functionalitiesof transmitters, devices with digitalinputs, devices with digital outputs,actuators, analyzers, and multi-variable devices.

The remaining parts of the profiledeal with the functionality of theindividual process device classes.In addition to this division, theprofile also draws a distinctionbetween class A and class Bdevices. A class B device hasadditional functions not supportedby a class A device.

4.2 Block model andsignal flow

The PA profile uses what is knownas a block model to describe

device functionality. The modelencapsulates individual functions inblocks and then represents theoverall function of a device bymeans of links between theseblocks. These function blocksdescribe the flow of themeasured/actuating signal withinthe device, i.e., how it is processedfrom sensor to fieldbus interface or from fieldbus interface to physicalactuator.

Figure 8 illustrates signal flow andfunction blocks using the exampleof a transmitter. The digital sensor signal is processed initially in anassociated transducer block (TB).Structured according to variousmeasured variables and mea-surement principles, the trans-mitter-specific part of the profiledescribes the functionality andassociated parameters of thetransmitter. Examples of TBfunctions, for example, include theconversion of the sensor value vialinearization characteristics (whichmay depend on the sensor used or

the properties of the process), theselection of the measurement unitor interference compensation.

The TBs output signal (primaryvalue) is then transferred to theinput of an analog input functionblock (AI), where the measuredvalue is processed independentlyof the specific measurementprocedure. If this process does notresult in a correct value, the AIfunction block will automaticallyswitch to a preset substitute value

Sensor andsensor signal

Digitalvalue

Transducer Block

FunctionBlock

Sensor andsensor signal

Digitalvalue

Transducer Block

FunctionBlock

Figure 8: Functional structure of PA devices


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or to the last valid measured value.The measured value is subject tocontinuous limit value monitoring. If it undershoots or overshoots theselimits, the alarm information will beset accordingly and a limit violationwill be indicated in the associated

status byte. Simulation modedisconnects the AI from the TB anda specified simulation value isprocessed by the AI.

The measured value madeavailable at the AI output isdetermined by the setting of thechannel parameter in the AI; itassigns the AI to a TB and can - ondevices with multiple sensors - beconverted to a different TB.

In addition to transducer andinput/output blocks, every PAdevice features an implementationof what is known as the physicalblock (PB). It is not part of thesignal flow but contains informationabout the device itself, e.g.,manufacturer code, serial number,installation date and diagnosticinformation. A complete overviewof a PA device in the block modelincluding data flows via the threedata channels MS0, MS1 and MS2appears in Figure 9. For moredetailed information, see the booktitled Profibus PA" referenced in

Chapter 9.

4.3 Device parameters

The individual data sheets of thePA profile define a set of profileparameters for each device class.Each of these parameters isassociated with a function block.Depending on the type of parameter, a distinction is madebetween input, output and internalFB parameters.

Input parameters can be assignedtheir value by the outputparameters of another block or bythe user. Input parameters areused to adapt device functionalityto a specific application. They canusually be set by a central stationon PROFIBUS and saved there for archival and documentationpurposes.

FB output parameters can belinked to the input parameters of other blocks. They can also beread via PROFIBUS, e.g., in order to provide information about thecurrent status of the device.Block-internal parameters are assigned

values used in internal FBcalculations and can usually onlybe read via PROFIBUS.

Where profile parameters areconcerned, a distinction is madebetween parameters which mustbe supported by every profiledevice in the associated class andparameters which are optional.Furthermore, the manufacturer of adevice is free to implement other parameters in a device, e.g., inorder to support the execution of amanufacturer-specific devicefunction. Every block also hasfixed, standard parameter components, e.g., the type of blockand the device class. The PAprofile specifies the function blockswhich must be implemented for each device class. In addition tothe functional description of thefunction block, a list of associatedblock parameters is also specified.This list contains the sequence of

the parameters as well as their attributes, e .g., data type, length,read/write access rights,input/output or internal parameters,memory characteristics andinformation about whether theparameter is required or optional.

The profile also specifies whether aparameter can only be transferredacyclically or both cyclically andacyclically. Typically, onlyindividual output parametersassociated with an analog inputand digital input block or inputparameters associated with ananalog output and digital outputblock are communicated.

Parameter addressing isaccomplished using the slot andindex model specified for acyclicreading and writing. The profileonly defines the relative position(relative index) of a parameter within the block. The number andtypes of implemented blocks, theslot and index of the firstparameter, as well as the number of parameters per block are allencoded in the directory object(DO) which can be read from slot1, index 0 and following indices onall PA devices.

Figure 9: PA device represented in the block model

P h y s i c al B l oc k Transducer Block

(Physical/Electrical)

Profibus-DP/PA

MS1 (acyclic)MS0 (cyclic)

Device = DPV1-Slave

ProcessProcess

Dev i c eManage

ment

( Di r ec t or y )

Prozess value,Status

Parameteri-sation

Operator views

FunctionBlock(s)FunctionBlock(s)

Diagnosisevents

MS2 (acyclic)

Profibus

Directory

P h y s i c al B l oc k Transducer Block

(Physical/Electrical)

Profibus-DP/PA

MS1 (acyclic)MS0 (cyclic)

Device = DPV1-Slave

ProcessProcess

Dev i c eManage

ment

( Di r ec t or y )

Prozess value,Status

Parameteri-sation

Operator views

FunctionBlock(s)FunctionBlock(s)

Diagnosisevents

MS2 (acyclic)

Profibus

Directory


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4.4 Operating profiledevices

The uniform, core functionality of PA devices in a device classsignificantly facilitates the

integration of PA devices intocontrol systems/plant assetmanagement systems. Device-independent drivers (profile GSD,profile EDD and profile DTM)mapping the functionality specifiedin the profile enable devices to beoperated without device-specificdrivers. Cyclic data traffic can beconfigured with a profile GSD. Aprofile GSD can be used tofacilitate the operation andinterchange of devices in the sameclass from different manufacturers.

In order for this to be possible, theID number of the device must beset to the profile ID number (parameter ID number selector inthe physical block). Profile GSDscan be obtained from the PI Website (www.profibus.com).

4.5 PROFIBUS in safety-related applications

Automation equipment having aneffect on or safeguarding plant

safety is subject to strict approvalrequirements in respect of the safeperformance of its safety function.These requirements are not simplyrestricted to automation devicessuch as sensors, actuators andcontrollers but also extend to thecommunication system connectingthese devices.

The PROFIsafe profile increasesthe transmission safety of thePROFIBUS protocol and has beenofficially approved for applicationsup to Safety integrated Level 3 (SIL3).

With PROFIsafe, PROFIBUS wasthe first communication standard tohave a communication layer developed in accordance with therequirements of internationalstandard IEC 61508 and, therefore,supporting the transmission of safety-related and non-safety-

related communication data via thesame communication medium. Theimplementation of the PROFIsafeprofile is independent of both thephysical transmission technologyand the application layer. Thismeans that the PROFIsafe

technology is equally compatiblefor use on process devices with thePA profile and for factoryautomation devices.

PROFIsafe has four ways of detecting data transmission errors:

Sequence numbering Time monitoring Unique identification of

communication peers Cyclic redundancy check

(CRC)

These safety measures areimplemented in the device softwarein the form of a safety layer superimposed on the PROFIBUSprotocol, which remainsunchanged. The safety layer checks the additional safety-relateddata received during cyclic dataexchange, indicating errors whenany are detected. In the sending of data, the safety layer generates thesafety-relevant data.

The device parameters transferredduring acyclic communication arenot subject to the data safetymechanisms specified in thePROFIsafe protocol. In order tomeet the requirements of functionalsafety with respect to deviceparameters, Appendix 1 of the PAprofile (Amendment 1, PROFIsafefor PA Devices) specifies aprocedure for starting up PAdevices under acycliccommunication conditions. As partof this procedure, the safety-relateddevice parameters have achecksum generation performedboth in the device and in theconfiguration tool. Only when bothchecksums match can the devicebe operated in a safety-relatedapplication with its current settings.It is not possible to change devicesettings during safety-relatedoperation.

In process automation, safety-related applications must take intoconsideration issues that go far beyond functional safety.

The required high availabilityof the sensors affects the

details and sequence of devicedevelopment and The term or property known as

"proven performance" (IEC61511) is of great significancein this respect. User guidelinessuch as the NAMURrecommendations NE 79 andNE 97 define requirements inthis respect.

It was already common practice inthe use of 4-20 mA technology touse proven-in-use field devicesfor safety applications. In order tofacilitate such use for morecomplex fieldbus communication,"proven-in-use" devices can beprovided with a bus interface andan "on/off" PROFIsafe layer. Thisallows users to continue to rely onone and the same device type for standard or safety applications.

4.6 Functions for deviceidentification and

maintenance support(I&M)

Identification and maintenancefunctions (I&M for short) describe aconcept for identifying PROFIBUSdevices and accessing device-specific information online via theInternet. I&M parameters describedevice-identifying parameters suchas manufacturer code, serialnumber, order number, hardwareand software version. Both theformat of the parameters and thecommunication services used toread them are identical for allPROFIBUS devices. An operator tool accessing I&M parameters canthen use the manufacturer code toaccess the device manufacturer'sWeb site. The assignment betweenmanufacturer code and Web URLis published on PI's Web site andused by the operator tool. Other


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EngineeringTool

MANUFACTURER_ID: 42PROFILE_ID: F600ORDER_ID: 6ES7 141-1BF00-0XB0

PROFIBUSWeb Server

PROFIBUSDevice

PROFIBUS

MS2

Manufacturer Web Server

ID Company Cust.

42 Siemens 0911-8...

Web

www.siem...

Service

http://.../

XML

EngineeringTool

MANUFACTURER_ID: 42PROFILE_ID: F600ORDER_ID: 6ES7 141-1BF00-0XB0

PROFIBUSWeb Server

PROFIBUSDevice

PROFIBUS

MS2

Manufacturer Web Server

ID Company Cust.

42 Siemens 0911-8...

Web

www.siem...

Service

http://.../

ID Company Cust.

42 Siemens 0911-8...

Web

www.siem...

Service

http://.../

XML

I&M parameters and parametersfrom the context of the operator tool are used by the tool inaccordance with specificregulations in Web URLs to

facilitate dedicated access todevice-specific online informationsuch as device documentation,GSD files or replacement parts. Inthis respect, I&M functions affectnot only the functionality of thePROFIBUS device but also createa concept spanning thefunctionality of operator tools, thecontent of Web URLs and theprovision of information on a Website.

Appendix 3 of the PA profile("Amendment 3, Identification andMaintenance Functions) describesthe relationship between I&Mparameters and their corre-sponding profile parameters(usually physical blockparameters), thereby linking theI&M specification with the PAprofile. I&M functions are specifiedindependently of the profile for allPROFIBUS devices supporting anacyclic communication channel.

4.7 Device diagnostics

Consistent diagnostics" of machines, systems and automation

devices provides huge potential for savings in the context of their operation, maintenance and repair.Intelligent field devices providegood requisite conditions since, inaddition to measured andmanipulated variables, they arealso able to provide operationalstatus information, e.g., remainingwear margin, number of operatinghours or even process-specificstates. This type of status anddiagnostic information must beunambiguous to provide a basis for making relevant and sounddecisions.

In principle in an automationsystem, there are three possibleusers of field device information:the controller, the system operator,e.g., for availability and validity of process values, and maintenance/service personnel, e.g., for locationand cause of faults needed for equipment replacement.

Adaptation to VDI/VDE andNAMURDevice-specific diagnostics and itstargeted distribution to varioususers without additional measures

having to be taken is a veryattractive feature of fieldbustechnology in comparison withconventional analog signaltransmission. The PA profile makesprovision for a diagnosticscapability of this type (seeAmendment 2, Condensed Statusand Diagnostic Messages). Interms of content, specific care wastaken to ensure compatibility withthe requirements of VDI/VDE 2650and its NAMUR equivalent NE107,closing a significant information

gap between fieldbus and controltechnology.

VDI/VDE Guideline 2650 Sheet 1and its NAMUR equivalent,recommendation NE107, requirethat the diagnostics informationprovided by the field device becategorized into what are known as"status signals" which must bemade available permanently by thedevice. The four status signals areanalogously:

Function check (C):Output signal temporarily invalid(e.g. frozen) due to ongoing workon the device.

Maintenance Request (M):Although the output signal is stillvalid, the wear margin is almostexhausted or, due to applicationconditions, e.g., caking, a functionwill soon be restricted.

Out of Specification (S):The device is operating outside of its specification, e.g., thepermissible physical measurementrange has been exceeded, and/or is operating under processconditions which may lead todeviations from measured valuesor setpoints, e.g., bubbling in thecontext of flow measurements.

Failure (F):Output signal invalid due tomalfunction in the field device or itsperipherals.

Figure 10: I&M functions supporting asset management


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PA devices transfer the measuredvalue status cyclically together withthe process value in the form of easy-to-interpret information aboutthe state of the field device. There

are four specific valuescorresponding to the four statussignals listed above.

Parameterization for thecurrent applicationThe assignment of diagnosticevents to a specific measuredvalue status is often only possiblesubject to the evaluation of themeasurement point with regard tothe specific application. For example, volume build-up on a

level limit switch would typically beassigned to the Maintenancestatus signal. However, in another specific process application,volume build-up might relate to aknown, process-specific build-up

which will be removed during thenext cleaning cycle. In this case,the Out-of-Specification statussignal would be more appropriate.

In order to adapt the assignment of diagnostic events to measuredvalue status in line with specificapplication conditions, the conceptalso supports an option to adaptthe "Diagnostic event - Measuredvalue status assignment made bythe manufacturer via parameteri-zation.

More detailed diagnosticinformationThe two guidelines cited abovealso propose going beyond the

scope of the classification of adiagnostic event as described andmaking available additional andmore detailed diagnosticinformation. This in turn makes itpossible, by means of appropriate

functions in the control system or plant asset management system(PAMS), to provide information onan individual basis to variousaddressees, e.g., operators and

maintenance personnel, viaparameterization.

The new diagnostics concept of PROFIBUS PA is a decisive stepon the road to comprehensiveasset management and asignificant shift from preventive or reactive maintenance to proactivemaintenance or conditionmonitoring. This provides a hugepotential for cutting costs, sincefield devices susceptible to wear,e.g., actuators or ph valueanalyzers, can be virtually fullyutilized since necessary serviceoperations can be scheduled in linewith the production scheduleand/or regularly scheduleddowntimes.

Figure 11: Assignment of a diagnostic event to a value of measured value status

PAMS

Control system level

PAMS

PROFI-

BUS

Field instrumentation

a

MesswertstatusC S F

PAMS

MesswertstatusC S FM

MesswertstatusC S F C S F

PAMS

C S FM

C S F

a) b)

M M M S FCM S FC

Control system Control systemValue status Value status Value status Value status

Value status Value status

Diagnosis events Diagnosis events

configurable configurable

configurable

allocation allocation

allocation

individually

PAMS


PAMS

PROFI-

BUS


a

MesswertstatusC S F

PAMS



PAMS

C S FM

C S F

a) b)

M M M S FCM S FC





configurable


allocation

individually

PAMS


PAMS

PROFI-

BUS


PAMS


PAMS

PROFI-

BUS


a

MesswertstatusC S F

PAMS


MesswertstatusC S F

a

MesswertstatusC S F

PAMS



PAMS

C S FM

C S F

a) b)

M M M S FCM S FC





configurable


allocation

individually

C S F

PAMS

C S FM

C S F

a) b)

M M M S FCM S FC





configurable


allocation

individually

PAMS


PAMS

PROFI-

BUS


PAMS


PAMS

PROFI-

BUS


a

MesswertstatusC S F

PAMS



PAMS

C S FM

C S F

a) b)

M M M S FCM S FMesswertstatus

C S F

PAMS



PAMS

C S FM

C S F

a) b)

M M M S FCM S FC





configurable


allocation

individually

C





configurable


allocation

individually


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5. Device integration

A particular advantage of PROFIBUS is its openness, whichin turn brings with it compatibilityacross a large number of deviceand system manufacturers.However, this does mean that thebenefit of numerous differentdevice and systems suppliers iscountered by a correspondinglyhigh number of different availableHMIs. Standards for the centraland uniform integration of fieldbuses into automation systemshave been developed in order toensure that a disproportionateamount of time and effort is notrequired with respect to installation,version management and deviceoperation. Devices are usually

integrated by means of mappingtheir functionality to operator software. The process is optimizedby consistent data managementthroughout the life cycle of thesystem, with identical datastructures for all devices. Allstandards cited in the followingsections can be used inconjunction with PROFIBUS.

5.1 General StationDescription (GSD)

The GSD is provided by the devicemanufacturer and is the electronicdata sheet for the communicationproperties of any PROFIBUSdevice. It is standardized in ISO15745 and supplies all informationnecessary to specify the cyclic I/Ocommunication with a PROFIBUSmaster and for the configuration of the PROFIBUS network. A GSDfile is in the form of a text-baseddescription. It contains keyinformation about the device, e.g.,

communication baud rates sup-ported, possible I/O configurations,any special features supported and

possible device diagnosticsprovided (if included by thevendor). The GSD alone issufficient to specify the cyclic I/Odata exchange of measured valuesand manipulated variables between

field device and automationsystem.

5.2 Electronic DeviceDescription (EDD)

The GSD alone is not sufficient todescribe the application-specificfunctions and parameters of complex field devices. A powerfullanguage is required to support theengineering system in handling theparameterization, service, mainte-nance, and diagnostics of the

devices. The Electronic DeviceDescription Language (EDDL),standardized in IEC 61804-2, isused for this purpose. It has beenfurther developed by the ECT(EDDL Cooperation Team), acooperative effort including PI, theHART Communication Foundation,the Fieldbus Foundation and theOPC Foundation.

An EDD is a text-based devicedescription which is independent of an engineering system's OS. Itprovides a description of the devicefunctions handled by acycliccommunications, including anygraphics-based functions. It alsoprovides device information suchas order data, materials, main-tenance instructions, etc.

The EDD provides the basis for theprocessing and display of devicedata by the EDD Interpreter. TheEDD Interpreter is the openinterface between the EDDs andthe operator program. It providesthe operator program with data for

visualization with a standard look &feel, regardless of device or manufacturer.

5.3 Device Type Manager (DTM) and Field DeviceTool (FDT) interface

Sharing the principles of the GSDand EDD technologies butexecutable-software-based rather than description-based, FDT/DTMtechnology created a method of device integration permitting avariety of different devices from allmanufacturers to be integrated andmanaged using a single piece of operator software. The DTM is anexecutable software componentcommunicating with the engi-neering system via the FDTinterface. The ongoing devel-opment of FDT/DTM technology isin the hands of the FDT Group and

is subject to internationalstandardization (IEC 62453).

A DTM is a device operator program by means of which devicefunctionality (device DTM) or communication capabilities (com-munication DTM) are madeoperational. It features thestandardized FDT (Field DeviceTool) interface with a frameapplication in the engineeringsystem. The DTM is programmedin a device-specific fashion by the

manufacturer and contains aseparate user interface for eachdevice. DTM technology is veryflexible in terms of how it can beconfigured. The FDT interface is amanufacturer-independent, openinterface specification whichsupports the integration of fielddevices into operator programsusing DTMs. It defines how DTMsinteract with an FDT frameapplication in the operator tool or engineering system.


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6. System technology

6.1 Paradigm shift inprocess automation

Process automation is charac-terized by a number of specificfeatures which determine the useof automation technology to asignificant extent: the service life of systems is frequently more than 20years; such systems often featurehigh risk potential and, therefore,demand that specific safetyrequirements are met; the use of proven-in-use devices and systemsis preferred; old and newtechnologies must coexist in such away that they are functionallycompatible.

This coexistence of old and newtechnologies is a particularlyrelevant requirement wherecommunication between fielddevices, in-process componentsand control systems is concerned.The most frequently used standardfor transferring measured values or manipulated variables isconsistently the 4-20 mA signal,often superimposed with the HARTcommunication technology proto-

col. HART (Highway AddressableRemote Transducer) is a com-munication system stan-dardizedby the HART CommunicationFoundation (HCF) which supportsthe transmission of additional data,e.g., limit values, diagnostics data,and error messages via the 4-20mA signal.Where newer systems or systemexpansions are being installed, theuse of 4-20 mA technology hasgiven way to fieldbuses such asPROFIBUS PA or FF (Foundation

Fieldbus). In order for thesetechnologies to run side-by-side ina single system, integratedcommunication concepts arerequired.

PROFIBUS offers a particularlyeffective integrated communicationsolution for process automationwhich is essentially based on thefollowing technologies andconcepts: The standard PROFIBUS DP

protocol The various profile definitions The Remote I/O for PA

specification

The Profile for HART onPROFIBUS specification for the integration of the largenumber of installed HARTdevices into PROFIBUSsystems

The Profile for HART onPROFIBUS specification defines aprofile which is implemented onmaster and slave above layer 7and as such supports the mappingof the client/master/server model of HART onto PROFIBUS. Fullcompatibility with HART speci-fications has been assured bycollaboration with the HCF indrafting the specification.

The HART client application isintegrated in a PROFIBUS master and the HART master in aPROFIBUS slave, the latter servingas a multiplexer and taking over communication with the HARTdevices. A communication channelwhich works independently of theMS1 and MS2 links has beendefined for the transmission of HART frames. One HMD (HARTmaster device) can support anumber of clients.

6.2 PROFINET inautomation technology

Industrial Ethernet has been usedin automation technology since themid-eighties to network computersand controllers. Now, PROFINETprovides an Ethernet-basedcommunication system which isable to combine the benefits of office communication

(TCP/IP, http, SMTP, etc.) with therequirements of industrial com-munication (real time, determinism,etc.). In so doing, PROFINET turnsthe success of nearly 20 years'experience of Industrial Ethernet toits advantage. Real-time

applications and non-time-criticalprograms (Internet browsers, e-mail clients, etc.) from the officeworld can run on the same networkcable. The use of Ethernet resultsin a uniform company-widenetworking technology for bothoffice and production. The systemsupports communication through-out the production chainfrom thedelivery of materials through thevarious phases of the productionprocess and beyond to packagingand dispatch.

PI has specified the PROFINETtechnology as the Ethernetstandard for industrial automation.

Potential benefitsof PROFINETPROFINET facilitates vertical andhorizontal communication from the field level to the corporate man-agement level, thereby significantly

simplifying the link betweenproduction processes and systemsfor production planning and control,e.g., manufacturing executionsystems (MES) and enterpriseresource planning (ERP).PROFINET uses globallyestablished standard IT services

and offers scalable real timecommunication for all applications

HART clientapplication

HARTmaster

HARTserver

PROFIBUS DP

PROFIBUS master PROFIBUS slave HART device

HART communication

HART profile

7

1

2

HART profile

7

1

2

HARTcomm

HARTcomm

HART clientapplication

HARTmaster

HARTserver

PROFIBUS DP

PROFIBUS master PROFIBUS slave HART device

HART communication

HART profile

7

1

2

HART profile

7

1

2

HARTcomm

HARTcomm

Figure 12: HART devices operating via PROFIBUS


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in the automation sector. Bothreal-time and TCP/IP-basedcommunications can runconcurrently on the same cable.The technical integration of process data into the ITinfrastructure of the company is

thus much easier than is the casewith fieldbus solutions.

PROFINET for process automationNow that PROFINET is firmlyestablished in factory automation,its use is being introduced inprocess automation too. Thestrengths of PROFIBUS which haveserved it so well over the years,e.g.., consistent communicationmethods for process and factoryautomation, the safety and drive

technologies, and applicationprofiles for all important applicationshave all been adopted byPROFINET.

The integration of PROFIBUS PAinto PROFINET targets theprotection of investments inexisting PROFIBUS PAinstallations while also exploitingthe advantages of the PROFINET

technology. This is becauseinstalled PA devices can be used inPROFINET systems with nochanges. To ensure the ability tointegrate these devices into controlsystems or asset managementsystems, mapping onto PROFINET

has been added to the PA profile.

Integration of PROFIBUS PAinto PROFINETThe focus of the requirements onthe use of PROFINET in processautomation is the consistentintegration of PROFIBUS PA intoPROFINET. The proxy concept,which is responsible for conversionbetween the two communicationsystems at both the physical andcommunication layers, is part of

this integration. This means that itremains possible to use theproperties of the PROFIBUS PAtransmission technology developedspecifically for process automationwithout having to sacrifice thebenefits of PROFINET technology.In addition, there are industry-specific product offerings of PROFIBUS PA-compatible process

devices today that cannot beexpanded short-term to offer equivalent PROFINET-compatibledevices.

There are currently no plans todevelop PROFINET-compatible

devices for intrinsically-safe areasof process automation due to thelack of power over the bussolutions for Ethernet that wouldfacilitate the intrinsically-safesupply of power to devices similar to that supported by 2-wire MBP-IS.

PROFINET as acommunication mediumbetween control systemsIn addition to using PROFINET interms of the above scenarios,PROFINET is of great importancein the exchange of data betweencontrol systems. In this respect,PROFINET in automation systemswill also perform the task of acommunication backbone whichwill interconnect PROFINETdevices directly and PROFIBUSPA devices indirectly via proxysolutions.

FD

FD

FD

GGGG

PROFIBUS PA PROFIBUS PA

HMI HMI ES

HMI: Human Machine InterfaceES: Engineering stationFD: Field deviceG: Gateway (Proxy)

Controller Controller

FD

FDFD

FD

FDFD

FD

PROFIBUS DP

FD

FDFD

GG

FD

FD

FD

GGGG

PROFIBUS PA PROFIBUS PA

HMI HMI ES

HMI: Human Machine InterfaceES: Engineering stationFD: Field deviceG: Gateway (Proxy)

Controller Controller

FD

FDFD

FD

FDFD

FD

PROFIBUS DP

FD

FDFD

GG

Figure 13: PROFINET-based automation system


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7. Conformity andcertification

For products of different types andfrom different manufacturers to beable to perform various tasks in the

automation process correctly, theymust exchange information over the bus without errors. Aprerequisite for this is a standards-compliant implementation of thecommunication protocols andapplication profiles by the devicemanufacturers.

Certificates are issued to prove thatthe many devices available (whichvary considerably frommanufacturer to manufacturer andin terms of their functional scope)conform to the communication andprofile specifications. Certificatesare issued by the PI certificationbody on the basis of a test reportfrom an accredited PITL. Thisprovides the user with addedpeace of mind with respect to theinteroperability and interchange-ability of products.

7.1 Quality control throughcertification

To ensure that products aredeveloped in accordance with thestandards, PI has established aquality assurance system wherebycertificates are issued for productsthat meet the necessaryrequirements as indicated in a testreport.

The aim of certification is to provideusers with an assurance thatdevices from differentmanufacturers are capable of fault-free operation when used together.

The devices are tested byindependent test laboratories inaccordance with the approved testprocedures. This makes it possibleto identify any misinterpretation of the standards by developers at anearly stage so that manufacturerscan take the necessary remedial

action before devices are installedin the field. The test also examinesthe devices compatibility with other certified devices. Upon successfulcompletion of the test, themanufacturer can apply for adevice certificate.

The certification procedure isbased on standard EN 45000. Inaccordance with the requirementsof this standard, the testlaboratories accredited by PI arenot associated with any specificmanufacturer. Only theseaccredited test laboratories areauthorized to carry out the devicetests that form the basis for certification.

The test procedure and sequencefor certification are described in theguidelines.

7.2 PA device certification

Figure 14 shows the basiccertification procedure for aPROFIBUS device (device under

test). The devices undergoautomated testing based on testscripts. All the results from theindividual test steps are recordedautomatically in the device test log.The quality system andaccreditation procedure together ensure a consistent level of testquality at the PITLs.

Test campaign intest laboratory

No

Yes

Certification

through PI

OK ?

Deviceunder Test

Test campaign intest laboratory

No

Yes

Certification

through PI

OK ?

Deviceunder Test

Figure 14: Test procedure for certification


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8. User benefits

The concepts of integrationinstead of user interfaces andOne technology instead of multipletechnologies mean thatPROFIBUS is able to generatesignificant cost reductionsthroughout the life cycle of asystem: during planning,installation, operation andmaintenance, as well as in thecontext of system expansions or upgrades. The provision of additional information such asdiagnostics data or supplementarymeasured values increases systemavailability and productivity.

PROFIBUS integration is based on

the standardized PROFIBUS DPcommunication protocol, whichsupports a variety of applications infactory automation and processautomation as well as motioncontrol and safety-related tasks.This integration proves its worthduring planning, assembly andservice while training,documentation and maintenanceare required to support only asingle technology. Users withhybrid automation tasks inparticular benefit from the uniqueability of the PROFIBUStechno

PROFIBUS PA System on

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