Fieldbus Glossary

« A B C D E F G H I J K L M N O P Q R S T U V W X Y Z »

« A »

Application Layer
The Application corresponds to Layer 7 in the ISO/OSI communications model. This layer is NOT the process application. It is the responsibility of this layer to provide protocols/services both internally within and between devices on a fieldbus. For FOUNDATION fieldbus the Application layer is described in two parts, the Fieldbus Message Specification Layer (FMS) and the Fieldbus Access Sublayer (FAS). The Fieldbus Message Specification Layer (FMS) allows easy access to data via object dictionaries and also the structuring of Virtual Field Devices (VFD s) allowing access to data via TAG s. The Fieldbus Access Sublayer (FAS) is where relationships such as Publisher/Subscriber and Client-Server are set up.
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Asynchronous communication
Describes communication where the transmitting device clock is not synchronised to the receiving device clock. Generally it indicates that individual data characters are preceded by a start character and terminated with a stop character. The start and stop characters add extra overhead and reduce the effective transmission speed.
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« B »

Backbone
Often described as the home run cable or main trunk. It is the main communication highway acting as a source for other lines (spurs) from the control room. For PROFIBUS it is likeley that the backbone will be the high speed PROFIBUS DP and for FOUNDATION Fieldbus it would be the High Speed Ethernet (HSE)
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Balanced Transmission Line
A pair of wires carrying an AC Analogue or DC Digital signal with both sides isolated from ground.Both ends must be terminated.This describes the transmission for H1 fieldbus.
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Bandwidth
The difference between the maximum and minimum frequency which can be transmitted along a network.This relates to the maximum data /information carrying capacity of the network.
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Blocks
Blocks are used to collect together related data in a single structure.Blocks can be interconnected or ‘soft-wired ’to perform more complex functions. See Function Block, Resource Block, Transducer Block
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Broadcast
A communications method where one device transmits onto the network and many devices read the data.The transmitting device does not get acknowledgement that all the devices who wished to receive the data actually received it. See Publisher/Subscriber and Token Passing
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Bridges
A Bridge allows to connect different segments using the same media access method i.e. the segments may operate at different baud rates. Unlike repeaters,which simply repeat the data on the input port onto the output port,a bridge will allow you to filter only the data that needs to be transferred to the other segment, so reducing communications traffic. A Gateway provides a similar function but extends it to transfer data between protocols (Between FOUNDATION fieldbus and PROFIBUS-PA)
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Bus
The Trunk / Backbone / Homerun with all the devices connected to it. See also Topology.
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« C »

CFF Capability File - values File
This is a file required by the FF Interoperability Test Kit V4 tick mark that provides configuration tools and host systems detail required for device integration. The type of information contained within a Capabilities file includes device functional capabilities,size and resource limitations,manufacturer-specific default values,network management and system management capabilities supported.Examples of the type of data stored in the Values file are: Device information,address,id,tag Network management and system management configuration data Function block schedules Communications settings and parameters Function blocks,parameters,link objects,trend objects,views,program invocations,and tag information It is the CFF file which allows an FF device to be configured off-line.
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Chicken Foot
Describes a network consisting of a number of devices connected to one Junction Box.
See also Spur, Segment, Topology.

Note:
- The sum of all the spur lengths and segment length should not exceed the maximum for the fieldbus cable i.e.Type ‘A ’ cable maximum =1,900m Segment length +All Spur Lengths <1,900m
- Maximum Spur Length is reduced by 30m for each device on the spur
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Collision Detection CSMA/CD
Describes a method for controlling data communication on a network. A device wishing to gain access to the network listens,if it hears silence it can then speak,if it then hears a collision it waits for a random time and then retries. Ethernet uses this type of control.
(CSMA/CD =Carrier Sense,Multiple Access with Collision Detection)
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Conditioner
A normal power supply would not be compatible with a fieldbus installation,as it would interfere with the fieldbus signal. A power supply (PSU) conditioner can be used to stop the fieldbus signal entering the power supply therefore making it compatible.The conditioner is usually an electronic equivalent of Inductor/Resistor.
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Coupler
The Coupler connects devices to the network.It can be simply terminals in a small box,plugs and sockets or specially designed DIN rail mounted connection units.It has at least 3 connections,One for the spur and one for each side of the trunk. An Active Coupler may contain components for signal amplification and retransmission.
A coupler in Profibus is a device that converts PROFIBUS DP to PROFIBUS PA. In this case the coupler is transparent to the system,as has no address or other functions. The coupler reduces the DP baud rate to 93.75Kbit/sec. See also Splice, Link Coupler
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« D »

DLL
Device Descriptions DD ’s are written in a special computer programming language called Device Description Language (DDL).The DD is used to allow the integration of an FF device into a configuration tool or system. For FF the DD is supplemented by the CFF file which allows for off-line configuration of the device and contains the so called "capabilities file"
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Deterministic
A deterministic communications protocol is predictable in the maximum time a device must wait in order to gain access to the network to make data transmissions. For real time control a deterministic protocol is desirable so that data transmission deadlines can be met e.g.for cyclic data transfers.In practice,even protocols designed to be deterministic,can become non-deterministic when a random error occurs in a message. So,in the real world one can only speak about a probability of successfully transmitting a message when access to the network is gained. The possibility of errors tends to equalise the differences in the Ethernet and Central control token approaches.
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Device
A physical entity connected to a fieldbus that is composed of at least one communication element.E.g.Pressure transmitter. See also Host.
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Device Description (DD)
Device descriptions are provided to host systems so that the host can "interpret"the meaning of the data provided by fieldbus devices.The DD knows the indices in the Object Dictionary of the device,so the host can use it to access variables. The DD is a clear unambiguous structured text description that precisely describes the field device data and operations to host systems.This text file is then passed to a tokenizer tool that generated the binary DD used by the host.
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Device Type Manager (DTM)
A Device Tape Manager (DTM) is a software program which interfaces to the Field Device Tool (FDT) to provide engineers with 100%access to configure a field device with a rich graphic user interface(GUI). The GUI is the same regardless of configuration tool used.The DTM is provided by the device manufacturer (CD ROM).
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« E »

Ethernet
Ethernet see also FOUNDATION fieldbus-HSE and PROFINet Network protocol commonly used to link PC ’s.10BASE-Tx(10Mbit/sec)100BASE-Tx(100Mbit/sec) -100BASE-Tx most popular today Runs over 2-pair (twisted)Category 5 cable -100BASE-T4 Runs on 4-pair (twisted)Category 3,4 or 5 cable -100BASE-FX Runs on two strands of 62.5/125micron fibre
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End Delimiter
A bit sequence used to signal the end of a frame. See also Frame,start delimiter
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« F »

Fast Ethernet
A term to describe Ethernet at 100Mbit/sec as opposed to 10Mbit/sec. See also Ethernet, FF-HSE
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Field Device Tool (FDT)
The Field Device Tool is a method to provide a set of standard interfaces from an engineering tool to the Device Type Manager (DTM). If your configuration tool of choice supports FDT then you can use the advanced features of the DTM to configure your field device. Supported by PROFIBUS and HART.
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Fieldbusses
A fieldbus is a method to allow digital communications between field devices including control room equipment. There are many fieldbusses available each one providing advantages for particular applications. For process control including devices such as pressure transmitters then the most suitable protocols would be PROFIBUS PA/DP and FOUNDATION Fieldbus, as they both supply power on the network. LON and DeviceNet are examples of sensor busses that cater for simple devices such as status switches.
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Flexible Function Blocks (FFB)
In addition to standard function blocks,vendors are able to define their own blocks for vendor-specific purposes. These blocks are called Flexible Function Blocks. A Flexible Function Block (FFB),defined in FF-894 FBAP part 5, is an application-specific Function Block,whose input,output and contained parameters depend on its actual algorithm.The definition of Flexible Function Blocks is independent of the programming language of the algorithm and the device structure.It might thus be used for a wide range of different programming systems,even though it is designed to fulfil the specific requirements of the Manufacturing Automation world and they ’re standardized programming language defined in IEC 61131-3.6.2.3.2.1 FFB is a "Wrapper" for an Application--specific Algorithm. Extends FB Model into Discrete Manufacturing. FFB ’s can be found in HSE devices.
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FOUNDATION Fieldbus
has worldwide usage and it allows for distribution of control to the field, time stamping of alarms at the field device,has extensive interoperability features and a unique User Layer for advanced functions. See the configuration how FOUNDATION Fieldbus uses two bus types: High Speed Ethernet (HSE) and Foundation H1

- FOUNDATION HSE
This is the High Speed bus for the FF protocol. It’s main function is for the connection of H1 segments to a central host and also connection of complex or externally powered device. FF-HSE supports all the functions present in H1 (Function blocks – deterministic communications – etc) and allows for the communications between H1 segments. A Linking Device is required to connect H1 to FF HSE and this device would often contain the LAS function. ABBs Linking Device LD 800HSE connects up to four H1 segments to HSE.

- FOUNDATION H1
This type is used for communication between field devices e.g. Pressure transmitters, which build up the H1 links.
It allows the distribution of control functions into the field device. A Linking Device is required to interconnect H1- links and FF HSE. FOUNDATION H1 devices have to pass independent testing to obtain the FF tick mark, this testing has been extended to the Linking Device and also the HOST ( HIST) system. H1 devices would be configured via an engineers workstation connected at the HSE.
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FISCO Fieldbus Intrinsically Safe COncept
This is a set of rules to follow for the application of PROFIBUS PA into hazardous areas using Intrinsic Safety methods.The guidelines refer to segment lenths - power supply current limits and device Capacitance - Inductance and fault parameters.The FISCO method provide an easy to understand and implement method for IS application.
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Frame
A single set of data transmission from a device. See also End delimiter, Start delimiter.
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Function Block for FOUNDATION Fieldbus
A Function Block describes data and operations for self-contained control functions.There are many standard Function Blocks. Some parameters within them are the same across all Function Blocks (Universal), some are the same for similar Function Blocks (Function parameters) and some are the same for similar devices (Profile parameters).
See Resource Blocks, Transducer Block, Flexible Function Blocks, top

« G »

Gateway
A Gateway provides communications capability between fieldbusses of different protocols e.g. between FOUNDATION fieldbus and PROFIBUS. It is different to a Bridge in that protocol conversion occurs above the application layer rather than in the datalink layer. There is bound to be some loss of functionality as a result of the conversion between protocols.
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GSD
abbreviation for the german term Gerätestammdaten. A GSD is the device database file (also called ‘device datasheet ’) for PROFIBUSdevices.The GSD file, which is provided by the device manufacturer contains a description of the device. GSD files provide a way for an open configuration tool while reading the device information and recognizing the device characteristics. The format of the GSD file isclearly defined by the PROFIBUS standard. The configuration tool the GSD files into its internal data base and takes all characteristics of the individual devices into account. The advantage is that the configuration is very simple and can be done by a vendor-independent configuration tool. The GSD files are more limited than DDL ’s in the description that they provide.
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« H »

HART
Highway Addressable Remote Transmitter -open Master-Slave protocol for bus addressable field instruments.->Asynchronous Data transmission with ->Half duplex-Procedure according Bell 202 Standard with 1200 Bit/s. This is a method of transmitting data via Frequency Shift Keying on top of the 4-20mA process signal to allow remote configuration and diagnostic checking.Devices such as the ABB S900 and S800 can make these HART diagnostic messages available to Asset management systems (AMS)such as ABB Optimize IT.
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H1
This refers to the low speed,low power fieldbus signalling at 31.25 kbit/sec. FOUNDATION fieldbus H1 allows for Digital only inter-device communication -Publisher/Subscriber or Peer to Peer. Power on the bus.A device should be capable of operating within a voltage range of 9 to 32V. Time distribution with scheduled events (aids distributed control in the field) Alarm/Event reporting. Distributed control into the field device The H1 bus is connected to the FOUNDATION Fieldbus HSE via a Linking Device.
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HIST
This is the Host System Interoperability testing verifying the basic host functionality needed for interoperability. Functional Tests Supported in HIST: Initial Connection and Address Assignment Reading and Writing of Field Device Information Test of configuration of link objects and schedule Testing of Mode and Status Testing of Alarms and Events Testing of View and Trend Objects Testing of Block Specific Behavior Testing of the Device Description Support Testing of the Capabilities File Support (need for offline configuration) There is no additional registration given to participants,but there is a Letter of Confirmation (LOC)for participants.
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Home Run
This is the communications cable that returns data to the Control Room. It is the main communication highway acting as a source for other line ( spur) from the control room.
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Host
A computer belonging to a user that hosts communication hardware and software that allows connection to the network. In FOUNDATION Fieldbus the term is also sometimes applied to a device containing the Link Active Scheduler (LAS). Examples are control room hosts,hand held configuration tools etc.
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HSE High Speed Ethernet
In the fieldbus context HSE is the FOUNDATION fieldbus High Speed Bus (FF HSE).
see also Ethernet
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Hub ( Ethernet)
This device repeats the input signal onto all ports. You can consider it to be a Multi-port repeater. It is used to create STAR network topologies for Ethernet installations. A Hub allows all connected devices to share the same network resources (bandwidth). Switches are now replacing hubs as a switch will filter messages between networks allowing improved network designs for optimum network performance.
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« I »

IEC
International Electrotechnical Commission
The standardisation Organisation responsible for the agreement of an international fieldbus standard.
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Inrush Current
Maximum allowed rate of change of quiescent current after a device powers up (non-transmitting). It should not exceed 1.0 mA/msec after the first 20msec of connecting a device to a network or after 20 msec after applying power to the network. See Maximum Current,Lift Off Voltage.
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Instantiation
A feature available in some FOUNDATION devices where the end user can select how many instances of a function block exists in a device. For example all transmitters will provide at least One Analogue Input (AI)Block, if the device supports Instantiation then the end user can add AI blocks as required (there will be a limit).
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ISO
International Standards Organisation

ISO-OSI Model
This is a model (defined by International Standards Organisation - Open Systems Interconnection (ISO/OSI)) containing 7 layers. Each of them describes a function(s) used to produce an open communications protocol. FOUNDATION fieldbus uses 3 of these layers plus an extra layer (User Layer).

The User Layer contains the function blocks to build process applications e.g. PID Controller or add extra functions.
The Object Directory. It also allows devices to set up communications relationships with each other (Publisher/Subscriber).
The Physical Layerdefines the speed of transmission, wave shapes and amplitude of signals. Also defines the transmission medium e.g. wire - fibre optic.

Instantiation
A feature available in some FOUNDATION devices where the end user can select how many instances of a function block exists in a device. For example all transmitters will provide at least One Analogue Input (AI)Block, if the device supports Instantiation then the end user can add AI blocks as required (there will be a limit).
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Intrinsic Safety
Method for limiting the amount of electrical power (~600mW) available to field devices. An IS power supply for a segment is likely to provide a voltage of less than 23V (typically will be 19V) and provide power for about 4 devices (assumes each device is loop powered and takes about 10mA) in the hazardous area. Protection can be via a Barrier or Isolator with the pros and cons of each being the same as for a traditional installation. See also FISCO
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Interoperable Systems Project
Historically, slow progress within the IFC (International Fieldbus Consortium) resulted in the formation of the Interoperable Systems Project (ISP), by a set of vendors, who decided to develop their own specifications based on PROFIBUS DP. A competing organisation, called WorldFIP was immediately formed by a different set of vendors basing their protocol on the French FIP standard.
However, users then found their systems suppliers on one-side and instruments suppliers on the other and pressure from them led to the dissolution of ISP and IFC and the formation of Fieldbus Foundation.
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« J »

Jabber
Refers to a network problem caused by a device placing corrupted data on the network,transmitting for too long,or an error condition due to an Ethernet node transmitting longer packets than allowed.
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« K »

KERMIT
Kermit is a popular file transfer and management protocol and suite of communications software programs with advantages over existing Internet protocols such as File Transfer Protocol and Telnet. It is freeware,developed and maintained by members of the Kermit Project at Columbia University.The Kermit protocol is described as "fast, robust,extensible,tunable,and medium-independent. In addition to the protocol support, the Kermit suite includes terminal emulation,character-set translation,and scripting. The suite can be installed on almost any operating system,including Windows,UNIX,DOS,VMS,OS/2,and a number of mainframe operating systems.
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« L »

Latency
The delay incurred by a switching device or a bridging device between receiving and transmitting data.
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Linking Device (LD)
This is a FOUNDATION fieldbus HSE device that allows to connect H1 segments to the FF High Speed bus. It often allows for the connection of more than one H1 segment (ABBs Linking Device LD 800HSE allows up to four H1 segments to be connected. It provides the LAS functions, too.)
The LD could be located near a process area to locally connect H1 segments to the high speed bus.
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Link Coupler
This often referes to a PROFIBUS DP to PA device which does not restrict the DP baud rate as is the case with the standard PROFIBUScoupler.
See Coupler
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Layers
Refers to the layered ISO/OSI model for specifying open communication protocols.
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Lift Off Current
See Inrush Current
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Lift Off Voltage
The initial voltage required for a fieldbus device to start operating.This should be 9V or lower. See also Inrush Current, Maximum Current
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Link Active Scheduler (LAS)
A device equipped with the LAS functionality controls which device on a FOUNDATION fieldbus network is allowed to transmit at any time.
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« M »

Manchester Bi-phase L
Manchester Bi-phase L is a signaling method for synchronizing receivers and transmitters.I t produces a pattern from which the information to synchronize the receiver clock can be extracted. It avoids the need for separate data and clock circuits. See Physical Layer
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Master-Slave
Describes a ethod for controlling data communication on a network. A master device controls which slave device can have access to the network to transmit data. An example protocol using this method is MODBUS RTU.
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MAU
The Media Access Unitbuilds up the interface circuitry between the bus and the rest of the communications circuitry in a device.The MAU regulates the current and shapes the trapezoidal waveform when transmitting. When receiving, it filters out the signal and extracts the bits.It also extracts the current from the network and supplies it to the device components.
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Maximum Current
A limit on the maximum device current applies during the interval 500 µs to 20ms after connection of a device to the network or after the application of power to the network.Limit is rated quiescent current +20mA.See also Inrush Current, Lift Off Voltage.
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Multi-variable device
See Sensor Fusion
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« N »

Node
Is a communications device on the network e.g.a pressure transmitter or valve.
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« O »

Object Directory (OD)
Provides a standard structure for accessing the internal data of a device. It defines the data types e.g.Integer, Boolean, Float, Date, String etc.The OD resides at the Application Layer. The OD is read by systems which then use the indices to access the data.
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« P »

Physical Layer
This layer defines everything required to make a physical connection to the fieldbus network.Both FOUNDATION and PROFIBUS use the same Physical Layer to the IEC 1158-2 standard. It defines Network medium (Wire-Optical fiber etc.) Wave shapes (square-Trapezoidal etc.) Wave amplitude Speed Startup and synchronizing of communications (Manchester Bi-phase L). Intrinsic safety (~6 devices).
See also ISO model
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Power Supply (PSU)
Fieldbus power supplies are different to traditional power supplies as they have extra components to stop the fieldbus signal from entering the power supply which would then corrupt it by regulating out the voltage variation.Traditional PSU can be upgraded so that they can be used in fieldbus installations by the use of PSU Conditioners. Redundant PSUs are possible and facilitated with devices such as PSU multiplexer from RELCOM. Maximim non-IS output is 32VDC max.For IS Output Depends on the barrier used (typically about 19V). See Surge Protectors , Segment , Inrush, Current, Maximum Current
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PNO
PROFIBUS Nutzerorganisation e.V.
The standardisation organisation driving the PROFIBUSfieldbus.
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PROFIBUS
PROFIBUS is a fieldbus protocol used in the Process Automation industry in a similar way to FOUNDATION fieldbus . It uses a multiple master and slave structure with predictable cyclic communications. PROFIBUS is common in Europe and exists in different versions: PROFIBUS DP Mainly used to communicate between PLC,systems or Bulk I/O devices. There is no power on the network -in Euronorm PROFIBUS FMS For PLC-PLC comms -in Euronorm. PROFIBUS PA For Process Automation For communication between field devices e.g. Pressure transmitters -in Euronorm Profibus-DP/V1:Decentralized Peripherals,Version 1.9 December 1996 (Draft)Quick,cyclic Data transmission . DPV1 adds the facility for Acyclic communications.
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Profiles
A profile defines what must be present (e.g.parameters or services) to provide a useful level of interoperability between devices from different vendors.
Device Profile defines minimum for interoperability between similar devices from different vendors.
Communication Profiles defines minimum for communications interoperability e.g.intelligent devices should support and time distribution services.
See Token Passing, Publisher/Subscriber,Collision Detection
Physical Layer profile defines the minimum characteristics for interconnection interoperability e.g. IS and non-IS power supply current and voltage levels.
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PROFINet
PROFINet provides the specification for the PROFIBUSprotocol to exist on Ethernet.The specification describes the use of component technology (COM/DCOM),COM object provides the interface to the PROFIBUS device. There is a requirement for a link device to connect PROFIBUS DP to Ethernet (will use proxy later)
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PROFISafe
The PROFISafe profile defines how failsafe devices (emergency stop pushbutton, light grids, interlocks) are connected to the programmable controllers via PROFIBUS.The methods to check the slave has received communications include consecutive numbering, time monitoring with acknowledgement, source-target identification and CRC control, as well as a patented "SIL Monitor".Not available at the PA level.
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Protocol This is the overall set of rules and formats for data transfer between the same ISO/OSI layers of different devices.
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Publisher Subscriber
Describes a particular transmission/reception method for sharing data on a network.A device can publish data to the whole network,all devices which wish to subscribe to that data will then read it.See Token Passing, Application Layer
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« Q »

« R »

Resource Block
The Resource Block describes the characteristics that apply to the whole of the physical device (e.g.manufacturer serial number).
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Repeater
Extending the length of the fieldbus is possible while using Repeaters. You can have a maximum of 4 repeaters in any direct communication path between two devices (maximum number of addresses is 240 for one home run). Repeaters for Ethernet have the same function as for fieldbus however there are two types of repeater available.
Type I :Converts the input to digital format and then repeats the signal on to the output port.This introduces a delay such that only one of these repeaters can be used on one segment. Could be used to connect differing media.
Type II :Instantly repeats input onto the output.Two of these repeaters can be used on one segment. The use of repeaters has to be balanced with overall network performance. As well as extending the distance repeaters allow more devices to be connected. Each additional device on the network will use up some of the bandwidth and as more devices are added performance will deteriorate.
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Round Board
A Round Board is a protocol converter usually manufactured by National Instruments or SOFTING. It can be used to make a HART device look like a Fieldbus Foundation device.
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« S »

Segment
A Segment is a length of Fieldbus network with a terminator at each end,or a part of a fieldbus network wiring that is electrically independent from other parts.It may or may not have an associated power supply. The number of devices on a segment depends on: Cable Type and Length IS or on-IS application Power Supply and Device current consumption Bandwidth available and required response
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Sensor Fusion
Sensor Fusion is the addition of intelligence and multi-measurement capabilities to devices such as flowmeters (DP flow -Temperature -Pressure).Take the example of compensated gas flow using a differential pressure transmitter,the traditional solution would require three devices (DP Pressure -DP gauge - Temperature) with three signal cables back to a controller/math unit.The equivalent Multivariable solution has one device carrying out DP and Gauge functions with a temperature probe connection,this device carries out all computation and relays the result over 4-20mA or a fieldbus.The ABB 2000T is an example of a multivariable transmitter supporting HART - PROFIBUS- FOUNDATION fieldbus.
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Service
Services are operations on communications objects of a defined class. A measured value, for example, is such an object that belongs to the class of Variables. Read and Write are the services allowed for this class of objects.
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Slow Speed fieldbus
See FOUNDATION Fieldbus H1 and PROFIBUS
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Splice
A part of the network in which the characteristic impedance of the network is not preserved e.g. connection to a spur using a different wire gauge.
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Spur
A Spur is a length of fieldbus network between a junction box and a device. A spur can vary in length from 1m (3.3 ft) to 120m (394 feet). A spur does NOT have terminators at either end of the spur cable.The maximum length of a spur depends upon several criteria including cable type and total number of devices on the segment.
Note:
- The sum of all the spur lengths and segment length should not exceed the maximum for the fieldbus cable i.e.Type ‘A ’ cable maximum =1,900 Segment length +All Spur Lengths <1,900m
- Maximum Spur Length is reduced by 30m for each device on the spur

Total Number of Communicating Elements	Maximum Spur Leng (M)
25-32	0
19-24	30
15-18	60
13-14	90
1-12	120

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Stack
Refers to the communications software suite that implements the ISO/OSI layers used in a device.
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Standards organisations
Worldwide standards are organised by the International Standards Organisation (ISO) and the International Electrotechnical Commission (IEC). A large number of national bodies support their work (see below). ISO covers standardisation in all fields except electrical and electronic standards which are the responsibility of the IEC. CENELEC is charted with developing voluntary electrotechnical standards as a basis for supporting the creation of a single European market without internal frontiers. Its work will override that of any European national group. Its work is primarily based on that of the IEC. The main bodies involved in the development of fieldbus standards are the ISA and IEC for FOUNDATION fieldbus and CENELEC for PROFIBUS,WorldFIP and Pnet (EN50170).

AFNOR	Association Francaise de Normalisation
ANSO	American National Standards Institute
ASME	American Society of Mechanical Engineers
BSI	British Standards Institute
CENELEC	European Committee for Standardisation
DIN	Deutsches Institut fur Normung
DoD	Department of Defence
EIA	Electronic Industries Association
ISO	International Standards Organisation
IEC	International Electrotechnical Commission
IEEE	Institute of Electrical and Electronic Engineers
ISA	Instrument Society of America
NEMA	National Electrical Manufacturers Associatio
SAE	Society of Automotive Engineers

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Start Delimiter
A bit sequence used to signal the start of the data portion of a frame. See also Frame, End delimiter
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Surge Protection Device (SPD)
This is a device that routes electrical surges (e.g.from lightning,welding)safely to ground.There is a fieldbus version of SPD that has a high bandwidth to pass the fieldbus signal. It also has a line resistance (typically about 10 Ohm.), that must be taken into account.
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Switches
An Ethernet device, which can be considered as a multi-port bridge.It can be used to replace a hub for the design of STAR topologies. A switch can filter messages between networks, so that devices connected to one switch share a local bandwidth. The Switch technology nearly enables FOUNDATION fieldbus to have deterministic communications.
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« T »

Token Passing
Deterministic method for controlling data communication on a network. Tokens (special data messages) are used to enable access to the network. In the simplest case a device will receive a token,which allows it to transmit on the network, all other devices listen.When the transmitting device has finished it passes the token to the next device and so on. Usually a device can hold the token only for a limited time before passing it on. In FOUNDATION fieldbus there is more than one type of token,these are:
Compel Token Initiates Broadcast (Publisher/Subscriber)communication. Pass Token Initiates peer to peer messaging. Probe Node Token Detects new devices on the network.
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Topology
Topology denotes the physical structure and layout of a network.In general,there are four types: Bus, Ring, Star and Tree.

BUS	A bus is a shared data transmission path by which all devices are connected.It has two defined ends.Each transmission propagates the length of the medium (usually cable)and is seen by all other devices.
RING	The devices in the network form a closed ring.Each device is connected to its neighbour.The data on the network is transmitted in one direction only and as it circulates through each device it is read by it.After circulating all round the ring it is removed by the source device.The failure of one device entails the failure of the entire network.
STAR	In a Star topology one central device performs all the signal switching and routing functions.The network is reliant on the performance of this one device.
TREE	A topology in which a number of junction boxes are connected along the network.Devices are connected in clusters at each junction box via spurs.This is also known as ‘Chicken Foot ’ topology.

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Transducer Block
The Transducer Block contains parameters specific to the technology of the device.Some parameters are standard for similar devices
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Terminators
Terminators are requires at the end of each fieldbus Segment and match the cable impedance to reduce reflections of the signal.
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Tree Topology
See Chicken Foot
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Trunk
A Trunk is the main communication highway acting as a source for other line (spurs) from the control room.
See also Backbone
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« U »

User Layer
Unique Layer found in FOUNDATION fieldbus to enhance interoperability and allow vendor innovation.Here you can use function blocks to build process applications e.g. PID Controller.
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« V »

Virtual Field Device (VFD)
Part of the Application Layer functionality. A Virtual Field Device is a model of the device for communications purposes. It groups variables into objects and then allows access to the data via an individual object dictionary (OD) for each VFD. This grants easy access to complex functions built up in a VFD. A physical device can contain one or more VFD s.
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« W »

« X »

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