Intro4u2u

Virtual Field Device (VFD)
A fieldbus device may have user applications,
which are independent from each other and do not
interact. A fieldbus device consists of Virtual Field
Devices for such individual applications. An
identifier, given to a VCR, identifies the VFD.
A Foundation device has at least two VFDs. One
is Management VFD where network and system
management applications reside. It is used to
configure network parameters including VCRs as
well as to manage devices in a fieldbus system.
The other is a Function Block VFD where Function
Blocks exist. It is possible for a field device to have
two or more Function Block VFDs.

1. Communication Models
1.1 OSI Reference Model
Communication specifications are often explained with reference to the Open System Interconnect
(OSI) layered model. FOUNDATION fieldbus is specified according to the simplified OSI model,
consisting of three (3) layers: Physical Layer (PHL), Data Link Layer (DLL) and Application Layer (APL).
See Figure A-1 for OSI model. Layers 2 to 7 are implemented mostly by software and therefore are often called the “communication stack.” Fieldbus Foundation specifies not only communication but also some user applications,
which use FOUNDATION fieldbus communication, though the OSI model does not specify any user application.
Application Layer of Foundation fieldbus consists of two sublayers: Fieldbus Access sublayer (FAS) and Fieldbus Message Specification (FMS). FAS is the “glue” to map FMS services to Data Link Layer.
Figure A-2 shows the architecture of FOUNDATION fieldbus.
1.2 Protocol Data Unit
Figure A-3 shows how a user data is transferred over the FOUNDATION fieldbus. Each layer appends layer-control information called Protocol Control Information (PCI) and more information to the message of the higher layer.
A data unit exchanged between the same layers is called “Protocol Data Unit (PDU).” A PDU may
contain an optional data called “Service Data Unit (SDU),” which is a PDU of the next higher layer. A
communication layer exchanges other PDUs without SDU to perform its functionality.

• Application Layer
• Presentation Layer
• Session Layer
• Transport Layer
• Network Layer
• Data Link Layer
• Physical Layer
• FMS Sub-Layer
• FAS Sub-Layer
• Data Link Layer
• Physical Layer

1.3 Communication through VCR
Messages are exchanged between applications sitting on the FOUNDATION fieldbus. When a
message is transferred, it goes down through a channel called Virtual Communication Relationship
(VCR) to add PCI before it goes to the wire. At the destination, it goes up through the partner VCR to
the receiving application. PCIs are appended and removed when a message goes through VCRs to
allow layers to perform their specific functionality. See Figure A-4.
A fieldbus device has many VCRs so that it can communicate with various devices or applications
at the same time. It is possible because the VCR guarantees the message goes to the correct
partner without risks of losing information. A VCR is identified by an application with device-local
identifier called “index” specified in Application Layer. It is also identified from other devices with
DL-address specified in Data Link Layer. A VCR has a queue (fast-in, fast-out memory) or a buffer
(memory to store data) to save messages.
It is the responsibility of network configuration to
give the correct information of the index and DLaddress
as well as other operating information to
VCRs through Network Management.
2. Physical Layer
Physical Layer is a mechanism to transmit and
receive electric or optic signals to/from medium so
that data consisting of ones and zeros is
transmitted from one node to the others. Physical
Layer interests are wires, signals, waveform,
voltage, and others all related to electricity and
optics.
Though the IEC/ISA standard specifies various
media with various speeds, Fieldbus Foundation
chose its own subset, low speed wire and fiber
media, and Ethernet. Ethernet is discussed in a
later chapter of this textbook.
2.1 31.25kbps Physical Layer
31.25kbps Physical Layer is the most common
since IEC and ISA approved it in 1992. This
textbook explains only wire medium but optical
fiber can be used as an alternative.
Though 31.25kbps sounds slow compared with the
latest telecommunication technologies, it is
necessary to replace traditional 4-20mA analog
transmissions. It is intended to apply to field
devices for various environments of industries.
Many users want to enjoy the simple installation of
two-wired transmitters. Explosive gases prevent
high-performance electronics in the hazardous
area of the plant. Transmission of 31.25kbps was
chosen for those applications, which demand
devices of very low power consumption.
A field device can draw electric current from the
medium to feed energy to its electronics. It is
called a “bus-powered” device and is the fieldbusequivalent
of two-wire installation.
2.2 Signaling Method
Fieldbus utilizes a similar technology for smart
transmitters to transmit an electric signal to the
wire. Figure A-5 shows the electric equivalent
circuit of signal transmission. Supply voltage is
applied by a power supply through an impedance
conditioner, typically consisting of inductors. DC
current through the impedance conditioner feeds
devices. Supply voltage is between 9V and 32V at
the device terminals. The impedance conditioner
makes output impedance of the power supply
higher than 400Ω in the signal frequency
bandwidth.
Each cable end is terminated with a terminator of
100Ω impedance. It makes an instrumentation
cable a balanced transmission line so that a signal
of relatively high frequency can be transmitted with
a minimum distortion.

Fieldbus is expected to reduce the life-cycle cost of production line and then total cost of ownership
(TCO) of the plant.
Planning Phase
Fieldbus allows you to integrate your plant assets on a single plant automation system on digital communication networks. You can connect devices from multiple suppliers without custom software and these network-based systems allow
for smaller control rooms, smaller cabinet rooms
and more information productivity.
Installation Phase
Fieldbus offers reduced installation and material
cost by replacing the traditional one-to-one wiring
scheme with networking or multi-drop
configuration, while intelligent field instruments
make commissioning and plant startup much faster
and less expensive.
Operation Phase
Fieldbus integrates various installations of control
functions into one system to effectively optimize
control of your plant. In addition, a unified humanmachine
interface (HMI) is provided for your
operation. Function Blocks allow control functions
to migrate into field devices allowing control
functions to move to the field.
Maintenance Phase
Fieldbus allows for the reporting of selfdiagnostics,
calibration, and environmental
conditions of field instruments without
disturbing the plant control. Since it uses
intelligent instruments, your stock for spare or
replacement instruments can be dramatically
reduced. Software packages for asset
management are useful to minimize
maintenance costs.
Renovation Phase
Enhanced functionality of field instruments is
endless. Fieldbus devices are becoming
standard off-the-shelf instruments, which make
it very cost-effective and easy for you to extend
the life of your plant. By simply connecting a
new device, you can immediately benefit from
advanced functionality. And, upgrade costs
can be reduced because network-based
systems are modular, which means they are
done on-line.
FOUNDATION Fieldbus
Fieldbus is not a product but a technology to make
above benefits available to end-users. The
following two conditions are necessary to make
them come true:
• Many vendors provide fieldbus instruments.
• Those devices are interoperable.
Fieldbus Foundation was established in 1994 to
achieve these goals. Its major activities are
• To promote a single international fieldbus to
both users and vendors,
• To deliver FOUNDATION fieldbus specification,
• To provide technologies for fieldbus
implementation including education, and
• To install an infrastructure to achieve
interoperability.
FOUNDATION fieldbus is a subset of IEC/ISA
standard (IEC61158 and ISA s50.02). Fieldbus
Foundation and its members adopt FOUNDATION
fieldbus as an enabling technology to utilize it to
bring the above benefits to end-users.

What is Fieldbus?
Fieldbus Foundation defines “Fieldbus is a digital,
two-way, multi-drop communication link among
intelligent measurement and control devices.” It is
one of several local area networks dedicated for
industrial automation.
Modern industries could not survive without
information technologies and networks in the 21st
century. From production line to enterprise level,
digital communication supports all economical and
social activities by its latest and powerful
technologies. Fieldbus is a part of it and cannot be
separated from others. Fieldbus is the lowest level
in the hierarchy and exchange information with
higher-level databases.
We have “standards” to transfer measurement and
control data between control room and plant floor.
They are pneumatic and 4-20mA electric signals.
We have enjoyed their finest features of
interoperability and easy maintenance. Smart
communication introduced in mid 80’s opened an
era of digital communication, but it had many
limitations such as proprietary protocols, slow
transmission speed and different data formats.
The idea of fieldbus was proposed to solve such
problems. A “standardized” digital communication
for industrial automation is changing the production
system very quickly.

FOUNDATION Fieldbus H1 (FF H1) supplies power and transmits communication digitally between host systems such as the DCS or a PLC and field instrumentation. Status information and control commands are transmitted between up to 31 participants connected to the same cable. Fieldbus is more than just pure process control. Remote configuration, asset management, and pro-active maintenance is all made possible with fieldbus.

FieldConnex is the right system to protect and integrate field device data into DCS. Simplistic by design, the reliable components provide ease of use and durability. Multiple Explosion protection concepts of choice make this the enabling technology for installation, commissioning, and dependable operation.

FF H1 conforms to IEC 61158-2. The Fieldbus Foundation is the governing body, it issues guidelines and definitions and ensures interoperability of devices. All constituencies such as plant operators, suppliers, contractors and DCS vendors are represented.

Fieldbus Device Couplers and Fieldbus Power Supplies
MooreHawke, the company formed from a recent acquisition by Moore Industries of Hawke International’s fieldbus products, provides FOUNDATION fieldbus ™/PROFIBUS PA Fieldbus Device Couplers and fieldbus power supplies that deliver industry-first advantages. This includes TRUNKGUARD™, the first fieldbus Device Coupler that provides fully automatic segment termination. This patented technology prevents fieldbus segment failure from under- or over-termination. Also featured are the patented ROUTE-MASTER™ I.S. Fieldbus Power Supplies. ROUTE-MASTER enables 350mA power per segment in intrinsically safe applications, which permits up to 16 fieldbus devices at 500 meters (1,500 feet) even in hydrogen-risk areas. Find out more about our fieldbus Device Couplers and fieldbus power supplies.
Fieldbus, Temperature Sensors, Signal Conditioners

We’re Your One Stop Temp Shop.
Moore Industries offers temperature transmitters, temperature sensors and fieldbus products to fit a wide range of process control applications. Site-programmable, PC-programmable, and HART-programmable models of temperature transmitters with temperature sensors are available with one of the industry’s most complete offerings of worldwide agency safety approvals. Isolated and RFI/EMI-protected, our temperature transmitters with temperature sensors can be easily programmed and installed on a DIN-rail, surface, relay track, pipe or in the field. We also offer complete temperature transmitters, temperature sensors and fieldbus assemblies. One simple model number is all it takes to order ready-to-install temperature transmitters with temperature sensors assembly. Find out more about our temperature sensors and fieldbus products.

Signal Conditioners Stop Problems and Increase the Capabilities of Your Control Loop.
Signal conditioners are available in 2-wire (loop-powered) and 4-wire (line-powered) versions. These signal conditioners provide up to up to 1500Vrms signal isolation and RFI/EMI protection. Our signal conditioners can be quickly programmed using on-board controls or a PC, for a broad range of input and output configurations. Signal conditioners isolate signals to stop erratic measurements caused by ground loops. Use our signal conditioners to interface field instruments with the control room, or to split one signal to allow one primary measurement to be sent to two separate systems.

The fieldbus system by the very nature of the environment in which it will be placed, is at risk from surges across the fieldbus system. Because the fieldbus system is controlling and handling the data transactions across a common trunk, the importance of safeguarding the integrity of the fieldbus system is paramount in order that the shutdown of multiple processes does not occur. These fieldbus solutions can be applied without impacting the length of the fieldbus run or the number of devices.

MTL surge protection devices supply complete fieldbus protection, whether for AC power, transmitter or trunk protection - MTL Surge Technologies supplies that power protection.

The adoption of fieldbuses in manufacturing continues to grow rapidly, especially in the heavy process industries such as oil & gas and chemical where the penetration of fieldbuses is still small. Manufacturers are realizing the benefits of homogeneous fieldbus architectures that enable industrial networking across domain boundaries from simple sensors to complex field instrumentation. PROFIBUS, with its common communications layer, many application profiles, and breadth of media alternatives, offers manufacturers a solid long-term value proposition to help protect their automation investments.

The value proposition of fieldbus has changed from the initial perceptions of the marketplace. Benefits such as reduced wiring and installation costs are apparent, but often mask the long-term benefits of fieldbus and device networks. According to ARC’s research, the greatest benefits of fieldbus and device networks are realized in the areas of maintenance and operations, long after a plant has been commissioned. In other words, fieldbus itself is often not the cost-saver, but merely an enabler to a new level of asset management effectiveness that can significantly reduce operating costs and help manufacturers achieve operational excellence. Many of the benefits of fieldbus are still being discovered as users gain more experience with these technologies in real world plant settings.

In typical process industries such as oil & gas or bulk chemicals, fieldbuses can contribute significantly to the achievement of operational excellence by enabling the sharing of critical information about the condition of devices. A fieldbus simplifies the gathering of data for Plant Asset Management (PAM) systems that watch over devices, tracking their “health”, and even detecting problems before they occur – a process known as predictive or proactive maintenance.

As a provider of humidity measurement technology, Testo has made a common field bus available: Profibus-DP. This has become standard in production automation and is also used for drying processes.

While humidity measuring systems in particular are sparking off a price war in air conditioning technology and requirements such as precision and system availability become of secondary importance, precision and reliability are key requirements in industrial humidity measuring technology for all those responsible for plants.

This applies equally to clean room applications and industrial drying processes.

Many of these applications, such as those in the food or pharmaceuticals industry, are embedded in an environment of factory automation in which readings are transmitted not only by means of analogue signals but increasingly via field buses.

Compared to alternative field buses, the humidity transmitter has established itself good. More than 20 million Profibus nodes (measuring points) have now been installed worldwide, and the voices which dismissed this humidity transmitter as merely the proprietary bus of all Siemens control systems have long been silenced.

In view of this, it is somewhat difficult to understand how or why humidity measurement has so far failed to make use of the Profibus connection.

Even highly-specialised analytical measuring variables are now available as Profibus versions; variables such as temperature and pressure are offered by well over a dozen providers with a Profibus output.

The situation in humidity measurement was rather different: none of the providers in this field have yet made the transition from analogue output or from proprietary digital outputs to an interoperative field bus such as the Profibus.

Testo AG has now closed this gap. With the new testo 6681 humidity transmitter, which offers optimum precision and calibration for every application due to digital probes, a humidity transmitter with a Profibus interface has been released.

Ideal for the user: The connection of the Profibus is designed as an intermediate layer, i.e. a sandwich design means that the Profibus interface can either be ordered ex works or be retrofitted on site at a later date. This retrofitting requires neither specialist knowledge nor special tools and can therefore easily be carried out by the customer.

Profibus and Profinet
applications user conference
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In June this year, Profibus UK has scheduled their fifth annual conference, renamed the Profibus and Profinet User Conference because of the growth in application and interest in Profinet

As a result of the excellent feedback from the previous events, the 2008 conference will continue to concentrate on the real issues of implementation, maintenance and management of Profibus and profinet systems, from a user perspective Speakers, many from the user community themselves, will present their experience as installers and users of such systems, with as much information about the problems to avoid, as about the advantages that result.

This article was originally published on Manufacturingtalk on 10 March 2008 at 8.00am (UK)
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The conference is designed for End-Users including installation and maintenance personnel, system designers and decision makers including managers - and indeed anyone concerned with the real issues of implementing fieldbus and/or industrial Ethernet technologies.

The conference programme is designed in a multi-stream format, to contain a mixture of technical presentations, demonstrations and hands-on practical sessions that are suitable for a wide variety of experience; from first-time users to those with extensive experience with working systems.

Some of these sessions will provide a taster of the training and technical support sessions provided by the UK profibus competence centre at the Manchester Metropolitan University (MMU), to support the further introduction of Profibus and Profinet technology into industry.

In addition, the Conference will cover latest developments in both Profibus and Profinet technology for factory and process automation, including safety, motion control, wireless implementations and integration with the internet and MES.

The two-day event will be supported by an Exhibition of the latest products from around 20 commercial and associated organizations, including leading product vendors, trainers, consultants and systems integrators: this free of charge Exhibition is open for any interested industrial visitor, whether attending the conference or not, subject to prior registration.
Further reading

Profisafe specified for wireless networks
Profisafe profile now specifies conditions for safely transmitting data via WLAN and Bluetooth and has been assessed and approved by the BGIA and TUV

Profinet now integrates with Hart
Draft specification for the integration of Hart into Profinet has been released in time for Interkama 2007

Maintenance operations guidelines for Profinet
Open integration path between MES and Profinet based automation systems by Dr Peter Wenzel, PI (Profibus and Profinet International), Karlsruhe, Germany

The venue this year is Stratford Manor, near Stratford-upon-Avon, in Warwickshire.

This hotel sits in its own 21 acres of grounds just 5 minutes from junction 15 of the M40, and is within easy reach of Birmingham International Airport.

It has recently completed a multi million pound refurbishment to give all the benefits of a modern Conference centre, providing a new larger venue and a great base for our 2008 event.

The conference dates will be Tuesday 24 and Wednesday 25 June.

DELEGATE INPUT.

The conference programme places great emphasis on serving the needs of the User community, i.e companies that own, operate, design, build or maintain manufacturing facilities and process plant.

The aim is to assist companies to plan, and to make the transition from conventional to fieldbus systems as easy (and jargon free) as possible.

As a part of this the sessions will include audience participation, and attendees are encouraged to submit the questions they wish to see answered in advance, for the presenters to cover that topic.

Further discussions with the presenters and suppliers can be developed during the conference breaks.

The programme of parallel conference presentations, hands-on practical sessions and exhibition mean that this event is a ‘must’ for anyone involved in, or thinking about, fieldbus, intelligent instrumentation and actuation, or networked control systems applications.

Supported by live demonstrations of the actual tools used in calibration and maintenance, the conference will be of great value to the System Engineers, C+I Engineers/Managers and Instrument Technicians/Engineers involved in the design, operation and maintenance of modern process and manufacturing plant.

Feedback from delegates in previous years has included ‘Good variety of presentations and good to have customers’ viewpoint to tell the negatives as well as the positives’; ‘Good insight for a person with limited knowledge of subjects covered, excellent workshop/primer sessions, useful exhibition’.

‘Will come again’; and ‘As a user in the Water Industry, the conference provided us with the necessary stimulus to decide to adopt Profibus technology more widely’.

‘The event provided a good balance between academic and practical subjects, and between workshops or lectures, with a good mix of suppliers and users also’.

‘The number of exhibitors gave confidence that Profibus is being widely supported, and that co-operation exists to evolve standards and products which will be inter-operable’.

To register for the conference, please complete and return the registration form available on the Profibus website, registration on line is also possible if you wish to pay by credit or debit card.