Smart Solutions For Automated Systems

Glossary List_2

2009-08-29T13:13:00.004+02:00

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Definition

Link

A Link is the logical medium by which H1 Fieldbus devices are interconnected. It is composed of one or more physical segments interconnected by bus Repeaters or Couplers. All of the devices on a link share a common schedule which is administered by that link's current LAS.

Link Active Scheduler (LAS)

A Link Active Scheduler (LAS) is a deterministic, centralized bus scheduler that maintains a list of transmission times for all data buffers in all devices that need to be cyclically transmitted. Only one Link Master (LM) device on an H1 fieldbus Link can be functioning as that link's LAS.

Link Master (LM)

A Link Master (LM) is any device containing Link Active Scheduler (LAS) functionality that can control communications on an H1 fieldbus Link. There must be at least one LM on an H1 Link; one of those LM devices will be elected to serve as LAS.

Link Object

A Link Object contains information to link Function Block (FB) Input/Output (I/O) parameters in the same device and between different devices. The Link Object links directly to a Virtual Communications Relationship (VCR).

MAC Address

A MAC Address is a unique hardware address given to each Ethernet interface chip.

Methods

Methods are an optional (but highly desirable) addition to Device Descriptions (DDs). Methods are used to define/automate procedures (such as calibration) for operation of field devices.

Mode

A Mode is a control block operational condition, such as manual, automatic, or cascade.

Network

A Network as applied in this document is the termination of one or more fieldbus segments into an interface card of the host system.

Comments: In this document, as has become industry practice, the term segment is used to represent a cable and devices installed between a pair of terminators.

Network Management (NM)

Network Management (NM) permits Foundation Network Manager (NMgr) entities to conduct management operations over the network by using Network Management Agents (NMAs). Each Network Management Agent (NMA) is responsible for managing the communications within a device. The NMgr and NMA communicate through use of the Fieldbus Messaging Specification (FMS) and Virtual Communications Relationship (VCR).

Noise AV

The Noise AV is the average noise in the network during the silence period between frames.

Object Dictionary

An Object Dictionary (OD) contains all Function Block (FB), Resource Block (RB) and Transducer Block (TB) parameters used in a device. Through these parameters, the blocks may be accessed over the fieldbus network.

Object Dictionary (OD)

OPC (Object Linking and Embedding for Process Control)

OPC is a software application which allows bidirectional data flow between two separate applications. These applications may be running on the same or on separate servers.

Operator Console

An Operator Console is a console used by an operator to perform the functions required to monitor and control his assigned units.

Physical Layer

The Physical Layer receives messages from the Communications Stack and converts the messages into physical signals on the fieldbus transmission medium, and vice-versa.

Quiescent Current

The device power consumption, the current drawn while the device is not transmitting. Shall be as low as possible to enable many devices and long wires, particularly in intrinsic safety.

Rate/Stale Count

Rate/Stale Count is a number corresponding to the allowable missed communications before a device will shed mode. This is basically a Watchdog Timer.

Redundant Configuration

Redundant Configuration is a system/subsystem configuration that provides automatic switchover, in the event of a failure, without loss of a system function.

Regulatory Control

Regulatory Control is the function of process measurement, control algorithm execution, and final control device manipulation that provides closed loop control of a plant process.

Resource Block (RB)

A Resource Block (RB) describes characteristics of the fieldbus device such as the device name, manufacturer and serial number. There is only one Resource Block (RB) in a device.

Schedules

Schedules define when Function Blocks (FBs) execute and when data and status is published on the bus.

Segment

A Segment is a section of an H1 fieldbus that is terminated in its characteristic impedance. Segments can be linked by Repeaters to form a longer H1 fieldbus. Each Segment can include up to 32 H1 devices.

Comments: In this document, as has become industry practice, the term Segment is used to represent a cable and devices installed between a pair of terminators. The Fieldbus Foundation specifications use the term Network to describe the system of devices though this document uses the terms interchangeably. See ANSI/ISA–50.02, Part 2 (IEC 61158-2): SEGMENT = The section of a fieldbus that is terminated in its characteristic impedance. Segments are linked by repeaters to form a complete fieldbus. Several communication elements may be connected to the trunk at one point using a multi-port coupler. An active coupler may be used to extend a spur to a length that requires termination to avoid reflections and distortions. Active repeaters may be used to extend the length of the trunk beyond that of a single Segment as permitted by the network configuration rules. A fully loaded (maximum number of connected devices) 31,25 kbit/s voltage-mode fieldbus segment shall have a total cable length, including spurs, between any two devices, of up to 1,900 m. There shall not be a non-redundant segment between two redundant Segments.

Self-Diagnostic

The capability of an electronic device to monitor its own status and indicate faults that occur within the device.

Splice

A Splice is an H1 Spur measuring less than 1 m (3.28 ft.) in length.

Spur

A Spur is an H1 branch line connecting to the Trunk that is a final circuit. A Spur can vary in length from 1 m (3.28 ft.) to 120 m (394 ft.).

Standard Function Block (FB)

A Standard Function Block (FB) is built into fieldbus devices as needed to achieve the desired control functionality. Automation functions provided by Standard FBs include Analog Input (AI), Analog Output (AO) and Proportional/Integral/Derivative (PID) control. The Fieldbus Foundation has released specifications for 21 types of Standard FBs. There can be many types of FBs in a device. The order and definition of Standard FB parameters are fixed and defined by the specifications.

System Management (SM)

System Management (SM) synchronizes execution of Function Blocks (FBs) and the communication of Function Block (FB) parameters on the fieldbus, and handles publication of the time of day to all devices, automatic assignment of device addresses, and searching for parameter names or "tags" on the fieldbus.

Tag

A Tag is a collection of attributes that specify either a control loop or a process variable, or a measured input, or a calculated value, or some combination of these, and all associated control and output algorithms. Each tag is unique.

Tag ID

A Tag ID is the unique alphanumeric code assigned to inputs, outputs, equipment items, and control blocks. The tag ID might include the plant area identifier.

Terminator

A Terminator is an impedance-matching module used at or near each end of a transmission line. Only two Terminators can be used on a single H1 segment.

Topology

Topology refers to the shape and design of the fieldbus network (for example, tree branch, daisy chain, point-to-point, bus with spurs, etc.).

Transducer Block (TB)

A Transducer Block (TB) decouples Function Blocks (FBs) from the local Input/Output (I/O) functions required to read sensors and command output hardware. Transducer Blocks (TBs) contain information such as calibration date and sensor type. There is usually one TB channel for each input or output of a Function Block (FB).

Transmitter

A Transmitter is an active fieldbus device containing circuitry which applies a digital signal on the bus.

Trunk

A Trunk is the main communication highway between devices on an H1 fieldbus network. The Trunk acts as a source of main supply to Spurs on the network.

User Application

A User Application is based on "blocks," including Resource Blocks (RBs), Function Blocks (FBs) and Transducer Blocks (TBs), which represent different types of application functions.

User Layer

The User Layer provides scheduling of Function Blocks (FBs), as well as Device Descriptions (DDs) which allow the host system to communicate with devices without the need for custom programming.

Virtual Communication Relationship (VCR)

Configured application layer channels that provide for the transfer of data between applications. Foundation fieldbus decribes three types of Virtual Communication Relationships (VCRs): Publisher/Subscriber, Client/Server, and Source/Sink.

Virtual Field Device (VFD)

A Virtual Field Device (VFD) is used to remotely view local device data described in the object dictionary. A typical device will have at least two Virtual Field Devices (VFDs).

Wizard

A Wizard is a means of automating procedures in Windows. Wizards can be used to implement methods.

Workstation

A Workstation is a set of electronic equipment including, at a minimum, one monitor, keyboard(s) and associated pointing device(s).

Glossary List_1

2009-08-29T13:00:00.006+02:00

Term Definition
Acyclic Period The Acyclic Period is that portion of the communication cycle time, during which information other than Publish/Subscribe data is transmitted. Typical information transmitted during this time includes Alarms/Events, Maintenance/Diagnostic Information, Program Invocations, Permissives/Interlocks, Display information, Trend Information and Configuration.

Application Layer The Application Layer is a layer in the communication stack containing the object dictionary.

Auto Sense Auto Sense is the capability of the system to automatically detect and recognize any hardware upon addition to, or removal from, the system without any user intervention.

Automation System A process automation, control, and diagnostic system that is composed of distinct modules. These modules may be physically and functionally distributed over the plant area. The automation system contains all the modules and associated software required to accomplish the regulatory control and monitoring of a process plant. This definition of automation system excludes field instruments, remote terminal units, auxiliary systems and management information systems.

Auxiliary System An Auxiliary System is a control and/or monitoring system that is stand-alone, performs a specialized task, and communicates with the automation system.

Basic Device A Basic Device is any device not having the capability to control communications on an H1 fieldbus segment.

Brick A Brick is a fully connectorized passive junction located on the bus.

Bus A Bus is an H1 fieldbus cable between a host and field devices connected to multiple segments, sometimes through the use of repeaters.

Capabilities File A Capabilities File describes the communication objects in a fieldbus device. A configuration device can use Device Description (DD) Files and Capabilities Files to configure a fieldbus system without having the fieldbus devices online.

Common File Format File (CFF) A Common File Format File is a software file used by the host to know the device detailed FF capabilities without requiring the actual device. This file format is used for Capabilities and Value files.

Communications Stack A Communications Stack is a layered software supporting communication between devices. It is the device communications software which provides encoding and decoding of User Layer messages, deterministic control of message transmission, and message transfer.

Configurable The capability to select and connect standard hardware modules to create a system; or the capability to change functionality or sizing of software functions by changing parameters without having to modify or regenerate software.

Configuration The physical installation of hardware modules to satisfy system requirements; or the selection of software options to satisfy system requirements.

Connector A Connector is a coupling device used to connect the wire medium to a fieldbus device or to another segment of wire.

Console A Console is a collection of one or more workstations and associated equipment such as printers and communications devices used by an individual to interact with the automation system and perform other functions.

Control Loop A Control Loop is a group of Function Blocks (FBs) that execute at a specified rate within a fieldbus device or distributed across the fieldbus network.

Coupler A Coupler is a physical interface between a trunk and spur, or a trunk and a device.

Cycle The scanning of inputs, execution of algorithms and transmission of output values to devices.

Data Link Layer (DLL) The Data Link Layer (DLL) controls transmission of messages onto the fieldbus, and manages access to the fieldbus through the Link Active Scheduler (LAS). The DLL used by Foundationfieldbus is defined in IEC 61158 and ISA S50. It includes Publisher/Subscriber, Client/Server and Source/Sink services.

Deterministic The ability to measure the maximum worst-case delay in delivery of a message between any two nodes in a network. Any network protocol that depends on random delays to resolve mastership is nondeterministic.

Device Description (DD) A Device Description (DD) provides an extended description of each object in the Virtual Field Device (VFD), and includes information needed for a control system or host to understand the meaning of data in the VFD.

DI Discrete Input – the signal is from the field device to the host system.

Discrete Control Control where inputs, algorithms and outputs are based on logical (yes or no) values. In the case of Foundation fieldbus, discrete includes any integer operation between 0-255.

DO Discrete Output – the signal is generated by the host system and transmitted to a field device.

EDDL Enhanced Device Description Language

Ethernet Physical and data link layer used by HSE fieldbus

Factory Acceptance Test (FAT) The Factory Acceptance Test (FAT) is the final test at the vendor's facility of the integrated system being purchased.

FF Foundation fieldbus

Fieldbus A Fieldbus is a digital, two-way, multi-drop communication link among intelligent measurement and control devices. It serves as a Local Area Network (LAN) for advanced process control, remote input/output and high speed factory automation applications.

Fieldbus Access Sublayer (FAS) The Fieldbus Access Sublayer (FAS) maps the Fieldbus Message Specification (FMS) onto the Data Link Layer (DLL).

Fieldbus Messaging Specification (FMS) The Fieldbus Messaging Specification (FMS) contains definitions of Application Layer services in Foundation fieldbus. The FMS specifies services and message formats for accessing Function Block (FB) parameters, as well as Object Dictionary (OD) descriptions for those parameters defined in the Virtual Field Device (VFD).
Comments: Network Management (NM) permits FOUNDATION Network Manager (NMgr) entities to conduct management operations over the network using Network Management Agents (NMAs). Each NMA is responsible for managing the communications within a device. The NMgr and NMA communicate through use of the FMS and Virtual Communications Relationship (VCR).

FISCO Fieldbus Intrinsic Safe COncept. Allows more power to an IS segment for approved FISCO devices, allowing for more devices per IS segment.
Comments: FISCO eliminates the requirement of calculating entity parameters of capacitance and inductance when designing networks.

Flexible Function Block (FFB) A Flexible Function Block (FFB) is similar to a Standard FB, except that an application specific algorithm created by a programming tool determines the function of the block, the order and definition of the block parameters, and the time required to execute the block. Flexible Function Blocks (FFBs) are typically used for control of discrete processes and for hybrid (batch) processes. A Programmable Logic Controller (PLC) can be modeled as a Flexible Function Block device.

FNICO Fieldbus Non-Incendive COncept. Allows more power to a fieldbus segment in a Zone 2 Area, thus allowing for more devices per segment.

Gateway A Gateway translates another protocol to fieldbus, for example HART to fieldbus or Modbus to fieldbus.

H1 H1 is a term used to describe a fieldbus network operating at 31.25 kbit/second.

H1 Field Device An H1 Field Device is a fieldbus device connected directly to an H1 fieldbus. Typical H1 Field Devices are valves and transmitters.

H1 Repeater An H1 Repeater is an active, bus-powered or non-bus-powered device used to extend the range over which signals can be correctly transmitted and received for a given medium. A maximum of four Repeaters and/or active Couplers can be used between any two devices on an H1 fieldbus network. Repeaters connect segments together to form larger networks.

High Speed Ethernet (HSE) High Speed Ethernet (HSE) is the Fieldbus Foundation's backbone network running Ethernet and IP.

HIST Host Interoperability Support Test performed by the foundation to test host conformance to the Foundation specifications.

HSE Field Device An HSE Field Device is a fieldbus device connected directly to a High Speed Ethernet (HSE) fieldbus. Typical HSE Field Devices are HSE Linking Devices, HSE Field Devices running Function Blocks (FBs), and Host Computers.

HSE Linking Device An HSE Linking Device is a device used to interconnect H1 fieldbus networks/segments to High Speed Ethernet (HSE) to create a larger system.

HSE Switch An HSE Switch is standard Ethernet equipment used to interconnect multiple High Speed Ethernet (HSE) devices such as HSE Linking Devices and HSE Field Devices to form a larger HSE network.

Input/Output (I/O) Subsystem Interface An Input/Output (I/O) Subsystem Interface is a device used to connect other types of communications protocols to a fieldbus Segment or Segments.

Instantiable The ability, for function block, to create multiple tagged function blocks of different types from a library as required by the application. Quantity per device restricted by device memory and other resources.

Interchangeability Interchangeability is the capability to substitute a device from one manufacturer with that of another manufacturer on a fieldbus network without loss of functionality or degree of integration.

Interoperability Interoperability is the capability for a device from one manufacturer to interact with that of another manufacturer on a fieldbus network without loss of functionality.

IS Intrinsic Safety

ITK Interoperability Test Kit used by the foundation to register devices and confirm compliance with the relevant Foundationstandards. This is a pass/fail test. Only devices passing the full suite of tests receive the foundation's official registration mark.

Junction Box / Quick Connection Station A Junction Box/Quick Connection Station allows for quick installation of four to eight field instruments via terminal connectors.

Fieldbus News-Press Releases

2009-08-23T23:28:00.004+02:00

FOUNDATION Fieldbus Developer Training To Be Offered During October In Austin, Texas
Vendor-neutral instruction covers key aspects of Foundation technology
AUSTIN, Texas, August 18, 2009 – The Fieldbus Foundation today announced it will offer Foundationfieldbus developer training during October 2009 at its headquarters in Austin, Texas. The vendor-neutral “Introduction to Foundation Fieldbus” and “Advanced Principles of Foundation Fieldbus” courses cover all key aspects of open, non-proprietary Foundation fieldbus technology.
Read more...

Fieldbus Foundation Announces FOUNDATION Positioner Transducer Block Final Specification
New specification release supports advanced field diagnostics capabilities
AUSTIN, Texas, Aug. 4, 2009 — The Fieldbus Foundation has announced that its Foundation fieldbus Positioner Transducer Block final specification is now available. The new specification release supports the implementation of advanced field diagnostics capabilities benefiting end-users of Foundation fieldbus technology.
Read more...

FDI Project Team Achieves Development Milestones
Karlsruhe, May 12th 2009 — The Steering Committee of the Electronic Device Description Language (EDDL) Cooperation Team (ECT) announces, that their technical team has achieved important milestones in its effort to develop a common solution for field device integration (FDI). The FDI Project Team has successfully worked over the past 18 months to identify use cases encompassing all facets of plant operations: from start up and commissioning; to ongoing maintenance activities and plant operations. It has also drafted an architecture concept migrating participating technologies to a common device integration standard.
Read more...

Fieldbus Foundation Announces Copyright Agreement With PROLIST® INTERNATIONAL
Fieldbus parameter names and definitions to be included in standardized device specifications
AUSTIN, Texas, June 3, 2009 — The Fieldbus Foundation today announced it has signed a copyright agreement with PROLIST® INTERNATIONAL. The agreement allows PROLIST to publish Foundationfieldbus parameter names and definitions in its standardized process control device/system specifications and database.
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Fieldbus Foundation EMEA Operations Joins Applied Control Technology Consortium
ACTC Undertakes Quantitative Evaluation of Foundation Fieldbus Control in the Field (CIF)
GLASGOW, Scotland, June 2, 2009 — The Fieldbus Foundation, through its EMEA Operations, has joined the Applied Control Technology Consortium (ACTC), based in Glasgow, Scotland. ACTC is wholly owned and managed by Industrial Systems and Control Ltd., a specialised control engineering consultancy with close links with the Industrial Control Centre at the University of Strathclyde, Scotland.
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FOUNDATION™ Fieldbus Developer Training To Be Offered During June At STC Brielle, The Netherlands
AUSTIN, Texas, May 20, 2009 – The Fieldbus Foundation today announced it will offer Foundationfieldbus developer training during June 2009 at STC Brielle, located in the Netherlands. The vendor-neutral “Introduction to Foundation Fieldbus” and “Advanced Principles of Foundation Fieldbus” courses cover all key aspects of open, non-proprietary Foundation fieldbus technology.
Read more...

Fieldbus Foundation Conducts Press Briefing at Interkama 2009
HANNOVER, Germany, April 21, 2009 — The Fieldbus Foundation, conducting a press briefing at the INTERKAMA+ 2009 Trade Fair in Hannover, Germany, made the following announcements:
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Fieldbus Foundation Announces Updated FOUNDATION Fieldbus Host Test Kit
Host testing solution has been enhanced with powerful performance features
AUSTIN, Texas, April 9, 2009 – The Fieldbus Foundation today announced the release of its updated Foundation fieldbus Host Test Kit (HTK) DD Application Module (Version 1.1.0). This powerful test kit, driven by the foundation's End User Advisory Council (EUAC), includes hardware and software for testing the functionality of a fieldbus host and its conformance with the Foundation host profile specifications.
Read more...

Fieldbus Foundation Announces First Registered FOUNDATION Fieldbus Hosts
Host registration provides new level of consistency in multi-vendor fieldbus environment
AUSTIN, Texas, April 8, 2009 - The Fieldbus Foundation today announced that two initial FOUNDATION fieldbus host systems have passed its new Host Profile Registration Process. The registered hosts include Yokogawa's STARDOM™ Network-based Control System and CENTUM® VP Integrated Production Control System, and ABB's System 800xA Extended Automation Product.
Read more...

More...
Fieldbus Foundation Seminar Attracts 100 Attendees In Baton Rouge, Louisiana
First Educational Institutions Offering Certified FOUNDATION Fieldbus Training Announced
Marc Van Pelt Appointed Fieldbus Foundation Corporate Secretary
FOUNDATION Fieldbus Developer Training To Be Offered During May In Austin, Texas
Fieldbus Foundation Conducts Press Briefing at 2009 General Assembly
Fieldbus Foundation Announces 2009 North American End User Seminar Schedule
Wireless Cooperation Team Marks Progress
Fieldbus Foundation Announces 2009 General Assembly Keynote Speaker And End User Presentations
Safety Instrumented Functions (SIF) Final Specification and Development Tools Announced
Fieldbus Foundation 2009 General Assembly To Be Held in Yokohama, Japan
Fieldbus Foundation Releases Updated Interoperability Test Kit
FOUNDATION Fieldbus Seminar Attracts Large Crowd In China
Fieldbus Foundation Announces New FOUNDATION SIF White Paper
Fieldbus Foundation To Support ISA104 Demonstration At ISA EXPO 2008 In Houston
Fieldbus Foundation And ISA Announce Collaborative Wireless Initiative
Fieldbus Foundation Registers First H1 Fieldbus Cable
Fieldbus Foundation Establishes Central and Eastern European Marketing Committee
Fieldbus Foundation Releases Final Diagnostic Profiles Specification
Fieldbus Foundation Releases New Device Description (DD) Enhancements
Fieldbus Foundation Names DuPont Executive To Its Board Of Directors
Fieldbus Foundation Releases Final Device Coupler Test Specification
Fieldbus Foundation Demonstrates SIF Technology At Shell Global Solutions In Amsterdam
Fieldbus Foundation Conducts Press Briefing at Interkama 2008
Fieldbus Foundation Conducts 2008 General Assembly
Swedish Marketing Committee Successfully Starts 2008 Training & Marketing Schedule
Choosing The Right Technology For A Digital Automation Architecture
Fieldbus Foundation Establishes Swedish Marketing Committee
Fieldbus Foundation CIS&B Marketing Committee Delighted With End User Seminar
Fieldbus Foundation Releases Standard Temperature Transducer Block Specification
Fieldbus Foundation Releases H1 Cable Test Specification
Fieldbus Foundation Announces 2007-2008 Recipients Of JOG – FF Educational Scholarship
Successful Fieldbus Foundation EMEA End User and Marketing Conference in London, UK
Fieldbus Foundation Establishes Norwegian Marketing Committee
Fieldbus Foundation, HART and PROFIBUS Organizations Launch Wireless Cooperation Team
Fieldbus Foundation Releases Fieldbus End User Podcast
Fieldbus Foundation Releases Host Test Kit
Fieldbus Foundation Establishes Marketing Committee For CIS and Baltics Region
Fieldbus Foundation General Assembly 2008 To Be Held In Antwerp, Belgium
Fieldbus Foundation Outlines Technology Advancements
Fieldbus Foundation Brazilian Marketing Committee Names Officers
Fieldbus Foundation Announces Updated Host Profile Specification
Fieldbus Foundation Establishes India Marketing Committee
Fieldbus Foundation Establishes Brazilian Marketing Committee
Fieldbus Foundation To Conduct Educational Seminar In Brazil
Dr. Graeme Philp Elected Vice-Chairman To Fieldbus Foundation’s EMEA EAC
Fieldbus Foundation Expands SIF Demonstration To Include Multiple End Users
Fieldbus Foundation Delighted With Events At Interkama 2007
Fieldbus Foundation Names Pepperl+Fuchs Executive To Its Board Of Directors
Fieldbus Foundation Praises Unified Device Integration Solution
Fieldbus Training Centers Establish License Agreement
PODCAST: FOUNDATION Technology User Insights
WHITE PAPER: FOUNDATION Technology - End User Perspective on Automation Infrastructure
WHITE PAPER: ARC Market Study Focuses on FOUNDATION Technology Operational Exellence
New ASIC Offered For Foundation H1 Devices
Fieldbus Foundation Names Wes Meger To End User Advisory Council
Fieldbus Foundation Dominates Fieldbus Protocols In Process Industries
Fieldbus Foundation Demonstrates Technology Advancements At Interkama 2007
Fieldbus Foundation Finalizes General Assembly Agenda
Fieldbus Foundation Announces General Assembly Speakers
Recipients Of James O. Gray–Fieldbus Foundation Educational Scholarship Announced
Fieldbus Foundation Announces Site For 2007 General Assembly
First Fieldbus Foundation EMEA Conference at Mannheim, Germany
Fieldbus Foundation Announces Availability Of New Fieldbus Media Attachment Unit (MAU)
ISA EXPO 2006 Press Releases
Fieldbus Foundation Enhances Device Description Library
Fieldbus Foundation Releases Updated HSE Test Kit
End Users To Benefit From Fieldbus Foundation And NAMUR Working Group 2.6 Fieldbus Collaboration
Fieldbus Foundation Launches End User Demonstration Project For Safety Instrumented Systems
Fieldbus Foundation Supports ISA Committee Standardizing EDDL Technology
Yokogawa Executive Shuzo Kaihori Named To Fieldbus Foundation Board
Fieldbus Foundation Hosts 2nd Successful End User Council Meeting in Frankfurt, Germany
Fieldbus Foundation Releases Updated Specifications
Fieldbus Foundation Receives TUV Protocol Type Approval for Safety Instrumented Systems Specs

Installing Fieldbus

2009-08-23T23:06:00.007+02:00

Fieldbus (the use of digital communications networks for distributed instrumentation and control) is a wonderful technology with many benefits, but fieldbus installation requires some additional considerations over and above normal 4–20 mA projects.

Don’t get hung up on which fieldbus to choose. Fieldbus is a generic term for a variety of communications protocols using various media, but all are simply a means to an end. What you want at the end of the project is a satisfactory and functional control system, and practically every installation will use multiple fieldbuses to accomplish the many tasks required. For example, you may use Foundation fieldbus in the process plant, DeviceNet for a PLC network, and PROFIdrive to run motor drives. Every DCS can easily integrate all these functional plant buses into the ethernet-based control room bus.

In process control engineering, ‘fieldbus’ normally means Foundation fieldbus H1 (H1) or Profibus PA (PA); both fieldbuses are perfectly adequate and widely used around the world in refineries and process plants as modern-day enhancements to 4–20 mA two-wire devices. This article focuses on H1 and PA physical layer implementation.

Fieldbus power supplies

A fieldbus segment (Figure 1) begins at an interface device at the control system. On a Foundation fieldbus H1 system, the interface is called an H1 card; on a Profibus PA system, it is a Profibus DP/PA segment coupler. In terms of signal wiring and power requirements for the segment, H1 and PA are identical:

Minimum device operating voltage of 9 V
Maximum bus voltage of 32 V
Maximum cable length of 1900 m (shielded twisted pair)
Communications at 31.25 kHz, Manchester encoded.
The DC power required by devices on the bus is normally sourced through a fieldbus power supply or ‘power conditioner’ (Figure 2) which prevents the high-frequency communications signal from being shorted out by the DC voltage regulators. Typical power conditioners make 350 to 500 mA available on the bus and usually incorporate isolation to prevent segment-to-segment crosstalk.

In H1 segments, the power conditioners are separate from the H1 interface card and are often installed in redundant pairs to improve the overall reliability. For PA systems, the DP/PA segment coupler usually incorporates the power conditioning component. There is no absolute requirement for the DC source to be independent per segment, but most designs provide segment isolation via DC/DC converters.

Note that fieldbus power conditioners are not the same as commercial off-the-shelf power supplies which, if connected straight onto any segment, will immediately damp out all segment communications.

H1/PA systems carry both DC power and digital communications on the same wire pair, and a standard 24 VDC power pack would effectively short-circuit the communications signal. The power supply therefore requires low pass ‘conditioning’ to filter out that signal, and this conditioning may be ‘active’ (notch filters, etc) or ‘passive’ (series inductance).

Figure 2: A fieldbus power conditioner prevents the high-frequency communications signal from being shorted out by the DC voltage regulators. Typical power conditioners make 350 to 500 mA available on the bus.

Of course, fieldbus power supplies can fail while in service so it is usually a good idea to specify power supplies that are redundant, can be ‘hot swapped’, and have some sort of alarm that notifies maintenance or operations when a problem occurs. Another good feature is built-in surge protection to protect the DCS system from lightning impulses from the field.
Redundant supplies can be constructed as needed for Foundation fieldbus H1 segments, but Profibus PA segments are constrained by the standard DP/PA segment coupler design which incorporates field power conditioning within the DP/PA protocol converter and only allows redundant power conditioning in the fault-tolerant version.

Segment calculations
When calculating how many devices can fit on a fieldbus segment, the primary factors to be taken into account are the maximum current requirement of each device and the resistance of the segment cable (because of voltage drops along the length). The calculation is a simple Ohm’s law problem, with the aim of showing that at least 9 V can be delivered at the farthest end of the segment, after taking into account all the voltage drops from the total segment current.
For example, driving sixteen 20 mA devices requires 320 mA, so if the segment is based on cable with 50 Ω/km for the loop and a 25 V power conditioner, the maximum cable length is 1000 m to guarantee 9 V at the end.
Note that many users also specify a safety margin on top of the 9 V minimum operating voltage to allow for unexpected current loads and for adding additional devices in the future. Some users also allow a safety margin in case one or more fieldbus devices fail from a short circuit. We’ll discuss safety margins in Part 2 of this article.
The calculations must be done for each segment. An engineer must add up all the power requirements of all the fieldbus transmitters, valve controllers and other devices on the segment, and then factor in the length and resistance of all the cables to make sure that 9 V will be available at the farthest devices. Fieldbus devices can require anything from 10 to 25 mA, with 20 mA a reasonable estimate for mental calculations.
In most cases, the fieldbus device manufacturer will supply the necessary data, but be wary: sometimes they are mistaken. In one case, a customer found that valve controllers specified to draw 10 mA actually required 25 mA when configured in a particular way. When the plant powered up the segment, they found that discrepancy the hard way, and had to add an entire segment to accommodate the high-powered controllers.
Advice: Be certain you know the power requirements of every device you plan to install on a segment.

Terminators

In Foundation fieldbus H1 and Profibus PA, the communications signal is current modulated at 31.25 kHz, 20 mA peak-to-peak. Terminators are required at each end of the segment cable (the square ‘T’ boxes in Figure 1) to prevent line reflections (which may otherwise result from open-ended cables) and to source/sink the communications current.

Figure 3: A device coupler provides short-circuit protection on each spur. Some device couplers have automatic segment termination.

The terminator circuit is very simple — a 100 Ω resistor and 1 µF capacitor in series across the segment. The end-of-line resistor provides a nominal load for the communications signal, and the capacitor stops the DC supply draining through the resistor. Two terminators at 100 Ω gives a nominal 50 Ω load for the communications current (20 mA p-p) and a signal voltage for receiving devices of 1 V p-p.

If instruments worked during lab or staging tests, but don’t work in the field, in many cases it’s an installation problem. Simply put, the technicians didn’t set the segment terminators properly. Instruments can behave erratically, drop off the segment mysteriously and generally raise havoc — all because the terminations are not set properly.

Two terminators are required per segment, one at each end. With one terminator, the signal will be higher, and with three or four terminators, the signal will be lower. Many field devices won’t accept signals at 2 V peak-to-peak and may unexpectedly reset. With three or four terminators, the signal can be so low it is unusable. The absolute minimum signal that devices must be able to recognise is 150 mV peak-to-peak.

Some users may test a segment in a lab, or at the vendor site. In such a case, under carefully controlled conditions, the segment may actually work with incorrect terminators. However, they rarely work in the field when not terminated properly.

Careful installation management to ensure the correct number of terminators is essential. It is unfortunate that many installation subcontractors pay little heed to the terminators and either forget them completely or enable them all if they are part of the device couplers, neither of which allows the segment to operate properly. Often, physical inspection of junction boxes and field enclosures is the only way to locate and correct the terminator position, which is a significant delay to the commissioning process.

Most device couplers (Figure 3) use manual DIP switches to terminate couplers. In a segment, the last device coupler should contain the terminator (Figure 4), and all couplers between the last coupler and the H1 card should have their terminator switches set to off. Diagnosing the problem often requires physically examining each device coupler to determine if the switches are set properly throughout the segment.

Automatic termination

Automatic segment termination simplifies commissioning and start-up. It automatically activates when the device coupler determines that it is the last fieldbus device coupler in the segment; if it is, it terminates the segment correctly. If it is not the last device, it does not terminate the segment, since the downstream device coupler will assume that responsibility. No action, such as setting DIP switches, is necessary by the installer to terminate a segment properly.

If a device coupler is disconnected from the segment accidentally or for maintenance, the automatic segment termination detects the change and terminates the segment at the proper device coupler. This allows the remaining devices on the segment to continue operation.

Figure 4: Terminators (shown as square T boxes) must be turned on at the beginning and at the end of each segment.

Fieldbus cable
One of the central ideas of fieldbus for process control is that it should be as practical as possible. Power and signal shall be available on the same cable, and that cable should not be fundamentally different from conventional instrument cable already in common use.
Some cable manufacturers take advantage of the uninitiated by offering ‘fieldbus’ cable in the same way as they make ‘intrinsically safe cable’ (the same as ordinary instrumentation cable but with an alternate colour sheath at significantly extra cost). In general, if a cable is already in use for instrumentation and control, it is almost certainly fine for H1/PA use. Typically, 0.8 mm²cable is used, with shield on individual spurs and with an overall shield if used as part of a multi-core cable. Table 1 lists the typical cables used in fieldbus applications.

Table 1:Maximum length of cables.
Cable Type Description Size Max length
A Tristed pair with shield #18 AWG 1900 m
B Multi-twisted pair with shield #22 AWG 1200 m
C Multi-twisted pair without shield #26 AWG 400 m
D Multi-core w/o twisted pairs having and having an overall shield #16 AWG 200 m
Conventional instrumentation cable may not have digital communications parameters included on its data sheet (effective impedance at 31.25 kHz, attenuation rate in dB/km, etc) and so its performance in fieldbus applications cannot be guaranteed. The Fieldbus Foundation’s test specification for cable allows manufacturers to test conformance to a proper performance specification.
Advice: If you intend to use cable glands to seal the cable entry into a device coupler or junction box, check that the fieldbus cable used is properly round — many less-expensive two-wire cables have a distinct lay evident in the outer sheath of the cable and this will not seal effectively in the cable gland.
Fieldbus wiring
Fieldbus cable may be virtually indistinguishable from 4–20 mA cable, but field wiring techniques and accessories are definitely different. Fieldbus systems are simple to design because all of the device wire-pairs are connected in parallel but, in practice, any attempt to fill a box full of terminals and just ‘jump’ between all positives and all negatives will result in a ‘rats nest’ of cables within the enclosure. This may be acceptable in some plants, but will lead to all sorts of maintenance problems once the installers have left the site.
A better idea is to use device couplers — junction boxes specifically designed for fieldbus implementation. These units automatically provide the necessary system interconnections without confusion and greatly speed up the process of device installation. They should incorporate the required terminator with either manual or automatic activation.

Foundation Fieldbus

2009-08-23T22:35:00.007+02:00

FOUNDATION™ fieldbus - the path to the future

The Internet is having a major impact on information flows. Yesterday's hierarchical systems with vertical information flows are being replaced by systems that have a flatter structure and more diverse information flow patterns. In today's world, it is essential to construct networks that are integrated with the Internet and can make use of the information available on it.

More and more today, process instrumentation is being field networked. As both the quantity and quality of field information increase, new instrumentation technologies will surely develop. The following table summarizes the key differences between conventional systems and field networked systems.

Field wiring Info.
flow Quantity of info. Info.
type Control functionality Maintenance location Maintenance type
Conventional 4 to 20 mA system Point-to-point Uni-directional Single data value Measure-ment numerical value Centered on a control system Mainly in the field Corrective maintenance
Field network Multi-drop Bi-directional Multiple data values Various data types Optimally allotted to control system and/or field devices From a remote location Predictive maintenance
The field signals used in process instrumentation have been standardized so that control systems and field devices from a variety of suppliers can be interconnected using standard 4 to 20 mA analog signals. The FOUNDATION™ fieldbus standard developed by the Fieldbus Foundation™ constitutes the next level of standardization and it is designed to meet modern needs. In addition to having interconnectivity equivalent to that available using 4 to 20 mA analog signals in a conventional field network, FOUNDATION™ fieldbus allows multiple devices to be connected to a single FOUNDATION™ fieldbus, permits the interactive communication of various types of information, and enables the distribution in the field of intelligent functions including self-diagnostics and control functionality.

When FOUNDATION™ fieldbus was first proposed, more attention was given to its ability to convey multiple field signals over a single cable and the benefit this would have in reducing wiring costs. But now the focus is on its ability to transmit various types of information in addition to field signals and to distribute intelligence to distributed field devices. These features enable remote monitoring, real-time self-diagnostics, and proactive maintenance of field devices, as well as plant resource management using field communication. This will enable the costs of operating instrumentation systems to be greatly reduced.

2009-08-21T08:56:00.002+02:00

Profibus-evolution

RS485 cable type and speed

2009-08-17T19:44:00.005+03:00

The maximum permissible bus length depends on the transmission rate and the bus cable type. Different cable types (designation A to D) for different applications are available for connecting PROFIBUS devices either each other or to network elements (Linking Devices, Repeaters).

The electrical lines are shielded twisted two-wire cables with a circular cross-section. The RS 485 interface operates on voltage differences. It is therefore less sensitive to interference than a voltage or current interface. Depending on the transmission speed, segments can be implemented in lengths of from 100 meter to over 1000 meter. The bus cable to be used for the bus modules is specified in DIN 19245/EN 50170 as cable type A and can be used according to the following table:

Parameter	DP, Cable Type A
Cable Design	Twisted pair and shielded
Surge Impedance	135 … 165 Ohm at f =3…20Mhz
Operating Capacity	=<>
Loop Resistance	=<>
Wire Diameter	>0.64 mm
Wire Cross-section	>0.34mm2

From the line parameters specified above result the following bus segment lengths:

Transmission Rate in kbits/sec	9.6	19.2	93.75	187.5	500	1500	12000
Range in Meter/Segment	1200	1200	1200	1000	400	200	100

NOTE: In a PROFIBUS DP installation, a data transfer rate must be chosen which is supported by all devices connected to the bus. The chosen data transfer rate then determines the maximum segment lengths as shown above.

If other transmission rate shall be used which is not listed in the table above, an approximation can determine the permissible length through linear interpolation of two adjacent transmission rates from the table.

Calculation of a bus length against of two transmission rates:

A transmission rate of 3 Mbit/s shall be used. The transmission rates in the table close to this value are 1.5 Mbit/s with l 1.5 Mbit/s and 12 Mbit/s with l 12Mbit/s. Thus, you can calculate the line length l 3Mbit/s:

RS485 network limits

Up to 32 nodes (master and slaves) can be grouped in a single segment. When using more than 32 nodes, several segments linked to each other through repeaters (power amplifiers) are needed. Note that the repeater has to be considered as another bus node, since the integrated bus drivers are an additional load on the bus. It is recommended to use not more than three series-connected repeaters on a line. However, the number of repeaters in a single PROFIBUS network is limited to 9.

The maximum admissible distance between two bus stations in each PROFIBUS network can be calculated as follows:

(Number of repeater + 1) * Segment length

Number of repeater = The maximum number of repeaters connected in series.

Example:

The repeater manufacturer’s specifications allow nine repeaters to be connected in series.

The maximum distance between two bus stations at a data transfer rate of 1500 kbit/s is then as follows: => (9 + 1) * 200 m = 2000 m

Adding field devices to the RS485 network

A shielded twisted-pair copper cable is the hardware required for RS485 transmission. It connects all devices to the bus structure (line). The bus structure allows for non-reactive coupling and decoupling of stations or step wise commissioning of a system. Later extensions have no impact on stations that are already working on the bus.

When connecting the field devices it must be ensured that the data lines are not reversed. Always use a shielded data line to ensure high interference immunity of the system against electromagnetic emissions. The shield should be grounded on both sides and large-area shield clamps should be used for grounding to ensure good conductivity. Furthermore the data lines should be laid separately and away from all power cables. Never use spur lines for transmission rates > 1.5 Mbit/s.

A 9-pin D-Sub connector is primarily used to connect PROFIBUS devices on the bus, which complies with DIN 19245/ EN 50170. Normally connectors are used, which supports direct connection of the incoming and outgoing data cable.

This eliminates the need for spur lines and the bus connector can be connected and disconnected to the field device at any time without interrupting data communication. The type of connector suitable for RS485 transmission technology depends on the degree of protection.

To avoid signal reflections on the bus line, the line structure must be terminated by a bus termination resistor network at either end. The bus is terminated at each end of a segment with an active bus termination. Both bus terminators have a permanent power supply to ensure error-free operation. The bus terminator is usually switched in the devices or in the connectors.

RS485 installation recommendation

Problems with data transmission in PROFIBUS networks can be attributed to incorrect wiring or installation. These problems can often be solved using bus test equipment such as bus monitors, which are able to detect many typical wiring errors even before commissioning.

The list below helps to build up a RS485 network quick and accurate:

• Only use shielded and twisted-pair wiring as a RS485 bus line.

• Use a PROFIBUS bus connector plug to connect the RS485 bus segment.

• If the module is at the beginning or end of a bus segment, this connector must have an activated bus terminal resistor combination.

• Ensure that the bus segment connected to the RS485 interface is terminated at both ends.

• All PROFIBUS bus connector plugs in a network must be securely screwed onto the RS485 interfaces.

• Attaching or removing the bus connector plugs, inadequately attached bus connector plugs or loose bus wires within the plug can lead to malfunctions in the networks.

• Attach or remove the RS485 bus connector plug quickly and without twisting them.

Fieldbus Topology with RS485 (PROFIBUS DP)

2009-08-17T19:37:00.005+03:00

Bus length and speed

When a PROFIBUS network is installed, boundary conditions of the RS485 transfer technology must be observed. The electrical network uses a shielded, twisted pair cable. All subscribers are connected in a line-shaped bus. The transmission rate can be adjusted in steps from 9.6 kbit/s to 1.5 Mbit/s. For extremely time-critical PROFIBUS-DP applications, additional transmission rate of 3, 6 and 12 Mbit/s are possible. The maximum segment length depends on the transmission rate.

RS485 limits and network design

As described in the PROFIBUS RS485 specification, each bus segment can have a maximum of 32 active devices. In order to be able to connect a larger number of PROFIBUS DP devices, it is necessary to segment the bus. The segments are then interconnected with repeaters which amplify and refresh the data signals. Repeaters can also be used for galvanic isolation of bus segments or bus sections. Each repeater allows the PROFIBUS system to be extended by an additional bus segment with the maximum admissible cable length and the maximum number of fieldbus

devices. Repeaters increase the signal propagation times. This should be taken into account during planning.

Redundancy Concepts

2009-08-17T19:30:00.004+03:00

Using a redundant PROFIBUS system makes it possible to considerably increase the availability and thus the reliability in comparison with a single system. One particular advantage is scalable redundancy that begins with a redundant PROFIBUS transmission link, continues with a redundant master and ends with a redundant PROFIBUS slave.

Master redundancy

The AC 800M controller is linked to the PROFIBUS master module CI854A. When a CI854A module fails or bus communication is interrupted, the redundancy partner is automatically activated. A CI854A pair balances the data cyclically over a fast link.

Line Redundancy

Line redundancy requires a redundant transmission medium and a redundant bus connection on the PROFIBUS master. The two transmission media are electrical cables in the simplest case, or fiber optical cables for higher requirements. For optimal usage of line redundancy, master/slaves/links with two bus terminals are required.

NOTE: The ABB PROFIBUS master module CI854A has a build in line redundancy. For slaves with only a single PROFIBUS DP interface, the Redundancy link Module RLM 01 can be used to integrate the device in the redundant line structure.

The master, slave or link detects the failure of a line and continues communication over the intact redundant line. The requirements for line redundancy involve immunity to open circuit, short circuit and error adaptation in respect of cables, connectors, repeaters, media converters and links.

If the PROFIBUS slave has not been implemented a redundant PROFIBUS interface, and if, however, an analysis of the system availability shows the necessity of redundant PROFIBUS cabling, it is recommended to use a Redundancy Link Module RLM 01.

Slave redundancy

Slave redundancy refers to a situation in which at least redundant links/gateways and optionally redundant I/O modules are present. If a gateway module fails or a disturbance in communication occurs, the second gateway module takes over the task. The same principle applies to the I/O modules. The redundant module continues to record and/or output measured values in the case of an error. The connected sensors or actuators including the signal and command lines are generally

only set singly.

Fieldbus Topologies

2009-08-17T19:20:00.006+03:00

Line Topology

With this topology, the fieldbus cable is routed from device to device on this segment, and is interconnected at the terminals of each fieldbus device. Installations using this topology should use connectors or wiring practices such that disconnection of a single device is possible without disrupting the continuity of the whole segment.

Line Topology with spurs

With this topology, the fieldbus devices are connected to the bus segment through a length of cable called a spur. A spur can vary in length from 1 m to 120 m. A spur that is less than 1 m in length is considered a splice.

PROFIBUS provides a wide range of possible transmission rates. The permissible lengths of possible spur cables depend upon the transmission rate used. No spurs are permitted for transmission rates over 1,5 Mbit/s. With transmission rates less than 1.5 Mbit/s the total length of all spur cables should be less than 6,6 m. When using spurs with low transmission rates (93.75 kbit/s), the ratio between spur cable length and next bus termination should be at least 1:20.

NOTE: There is always a cable of several centimeters between a PROFIBUS connector and the transceiver of a node. When connecting 32 nodes to the bus, an important total spur cable length will result from this. If there should encounter transmission problems in the installation although everything works reliably at a low transmission rate, it is recommended to perform a dynamic bus analysis. This analysis will reliably detect mismatches.

Tree Topology

With this topology, devices on a single fieldbus segment are connected via individual twisted wire pairs to a common junction box, terminal, or I/O card. This topology can be used at the end of a home run cable as well as in between. It is practical if devices on the same segment are well separated, but in the general area of the same junction box. When using this topology, the maximum spur length must be taken into consideration. Maximum spur lengths are discussed in Line Topology with spurs.

NOTE: Combinations of the topologies above are possible. However, all rules for maximum fieldbus segments length, including spurs, must be taken into account for the calculation of the total bus length.

PROFIBUS DP

2009-08-17T19:12:00.005+03:00

The PROFIBUS DP (RS485) is responsible for communication between the Controller level of a process automation system and the decentralized periphery in the field, also intrinsic safety (RS485-IS) via DP-Ex barriers into hazardous area.

One feature of PROFIBUS DP is its scalable high speed of transmission up to 12 Mbit/s.

Each device, connected to a PROFIBUS network, needs a unique address for selectively identify a field device. For this purpose, PROFIBUS device addresses are assigned either by an address switch (hard addresses) or by parameter assignment during commissioning (soft addresses).

A 7-bit device address serves to identify the bus participants in the network. The addresses range from 0 to 127 and the following are reserved:

• Address 126: default for automatic address assignment via the master;

• Address 127: sending broadcast telegrams.

If the address 0 is used for the class-1 master, the addresses 1 to 125 are available for addressing the field devices. Therefore up to 126 DP or PA field devices (master and slaves) can be addressed. Each address can only be used once in a single PROFIBUS network.

RS485 is the most commonly used transmission technology for PROFIBUS DP. It uses a shielded twisted pair copper cable and enables transmission rates up to 12 Mbit/s. Because of its simply installation it is cost-effective and requires no expert knowledge.

The bus structure allows adding or removing of field devices as well as step by step commissioning without influencing the system. Later extensions have no impact on devices that are already working on the bus. RS485 is scalable in its transmission rate from 9.6 kbit/s up to 12 Mbit/s, which is set in the PROFIBUS master.

Profibus System Overview

2009-08-17T18:47:00.006+03:00

PROFIBUS is a manufacturer-independent field bus standard for applications in manufacturing, process and building automation. PROFIBUS technology is described in fixed terms in DIN 19245 as a German standard and in EN 50170 / IEC 61158 as an international standard.

It specifies the technical and functional properties of a serial bus system. The PROFIBUS standard is thus available to every provider of automation product. PROFIBUS distinguishes between master and slave. The masters determine the data communication on the bus.

A master can send messages without an external request if it has access rights to the bus (token). The slaves are peripheral devices. Typical slaves are I/O devices, valves, motors and transmitters.

They have no bus access rights. They can only confirm received messages or send a message on the request of the master. Slaves are passive devices on the PROFIBUS. PROFIBUS is composed of three types of protocol, each of which is used for different tasks. Of course, devices with all three protocols can communicate with each other in a complex system by means of a PROFIBUS network.

The three types of protocols are: PROFIBUS FMS, DP, PA.

Only the two protocol types DP and PA today are important for process automation and are supported within the 800xA System.

For this Project we will only be concentrating on Profibus DP (with a brief description of Profibus PA only to the extent of documentation).

PROFIBUS PA is an all-digital, serial, two-way communication protocol that connects field devices (instruments), such as sensors, actuators, and controllers.

PROFIBUS PA enables advanced diagnostics from all field bus components including the physical layer. This allows higher plant availability. A typical Field bus installation provides connection from a network of field devices via a segment coupler to a host system via a two way, serial communication link. The cabling and connections are arranged in a multi-drop fashion, requiring only a single pair cable with parallel connections to field devices.

PROFIBUS PA is different from the traditional approach of connecting 4 to 20mA devices to a DCS/PLC system using dedicated pairs of wires for each device.

Each Field bus running from the segment coupler to the field is known as a segment.

Each segment consists of a trunk or home-run, running from the segment coupler to the processing plant with parallel connected spurs linking to field devices such as transmitters and control valves.

Smart wiring blocks with integrated short circuit protection, such as Segment Protectors or Field Barriers, protect the trunk against short circuit on a spur.

Such protectors are preferred to connect the individual instruments to the trunk.

The interconnection from a PROFIBUS PA trunk to PROFIBUS DP is realized with a segment coupler.

Profibus

2009-08-10T15:58:00.008+03:00

The masters determine thedata communication on the bus. A master can send messages without an external request if it has access rights to the bus (token). The slaves are peripheral devices. Typical slaves are I/O devices, valves, motors and transmitters. They have no bus access rights. They can only confirm received messages or send a message on the requestof the master. Slaves are passive devices on the PROFIBUS. PROFIBUS is composed of three types of protocol, each of which is used for different tasks. Of course, devices with all three protocols can communicate with each other in a complex system by means of a PROFIBUS network.The three types of protocols are: PROFIBUS FMS, DP, PA.

Only the two protocol types DP and PA today are important for process automation and are supported within the 800xA System developed by ABB

Introduction to Fieldbus

2009-07-13T21:12:00.012+03:00

What is Fieldbus?

Fieldbus is a generic-term which describes a new digital communications network which will be used in industry to replace the existing 4 - 20mA analogue signal.

The network is a digital, bi-directional, multidrop, serial-bus, communications network used to link isolated field devices, such as controllers, transducers, actuators and sensors. Each field device has low cost computing power installed in it, making each device a ‘smart’ device. Each device will be able to execute simple functions on it’s own such as diagnostic, control, and maintenance functions as well as providing bi-directional communication capabilities.

With these devices not only will the engineer be able to access the field devices, but they are also able communicate with other field devices. In essence fieldbus will replace centralised control networks with distributed-control networks. Therefore fieldbus is much more than a replacement for the 4 - 20mA analogue standard.The fieldbus technology promises to improve quality, reduce costs and boost efficiency.

These promises made by the fieldbus technology are derived partly from the fact that information which a field device is required to transmit or receive can be transmitted digitally. This is a great deal more accurate than transmitting using analogue methods which were used previously. Each field device is also a ‘smart’ device and can carry out it’s own control, maintenance and diagnostic functions. As a result it can report if there is a failure of the device or manual calibration is required, this increases the efficiency of the system and reduces the amount of maintenance required.

Each field device will be more flexible as they will have computing power. One fieldbus device could be used to replace a number of devices using the 4 - 20mA analogue standard. Other major cost savings from using fieldbus are due to wiring and installation - the existing 4 - 20mA analogue signal standard requires each device to have is own set of wires and its own connection point. Fieldbus eliminates this need so only a single twisted pair wiring scheme is required.

The International DebateAlthough fieldbus technology has been around for the past 8 years it is still not widely used. The reason for this delay is due to the lack of an international fieldbus protocol standard which will ensure complete interchangeability and interoperability between different suppliers. The major players in the fieldbus debate are WorldFIP and ISP. The completion of a fieldbus standard is not forecasted until 1997 meaning there is still a long time to wait. With consumers becoming impatient many companies have decided to released there own systems which work off different standards.The WorldFIP standard is based on the Factory Information Protocol (FIP). It works on a distributed database and time-service system and has a bus manager which issues tokens on an accurate time basis which matches device requests. The InterOperable System Project (ISP) is based on Profibus, which controls messages by using a token-passing method where a token circulates through all participating stations and the station may talk while in possession of the token. The token is circulated according to a preconfigured timing.

There is a technical report which defines the full functionality of the user layer in the ISA’s SP50 version of the standard. The focus of the report is to define the complete distribution of data acquisition and control functions within the field devices. It is this layer on which a decision is needed to be reached to result in true interchangeability and interoperability. This would give users a free choice of equipment instead of having to be locked into using equipment which uses one of two totally different standards. Currently both WorldFIP and ISP organisations are both trying to implement as many high level control functions as possible in to their new fieldbus products, Therefore we may be on the path to two different standards.
Fieldbus is no longer simply a communications standard but is a complete open, integrated measurement and control system which is looking to change the face of process control forever.

Here is a tutorial shows you the way to Fieldbus,its very useful for begginers and also experts.

Introduction to Fieldbus

Cable Type	Description	Size	Max length
A	Tristed pair with shield	#18 AWG	1900 m
B	Multi-twisted pair with shield	#22 AWG	1200 m
C	Multi-twisted pair without shield	#26 AWG	400 m
D	Multi-core w/o twisted pairs having and having an overall shield	#16 AWG	200 m