Fieldbus Solutions Glossary

In an effort to help both suppliers and end users of controls and instrumentation better understand FOUNDATION technology, the Fieldbus Foundation has provided the following "glossary" of common fieldbus-related terms.

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

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.

Communications Stack — A Communications Stack is device communications software which provides encoding and decoding of User Layer messages, deterministic control of message transmission, and message transfer.

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

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.

DCS — Distributed Control System

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 FOUNDATION fieldbus is defined in IEC 61158 and ISA S50. It includes Publisher/Subscriber, Client/Server and Source/Sink services.

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.

Foundation Fieldbus — 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. It is designed to be compatible with the officially sanctioned SP50 standards project of the ISA and the specifications of the IEC.

Fieldbus Foundation — The Fieldbus Foundation is a consortium of leading controls and instrumentation suppliers throughout the world. Its purpose is to accelerate development and acceptance of a single, open, interoperable fieldbus specification, as well as hardware and software technology for companies that wish to implement it in their automation products.

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).

Flexible Function Block — A Flexible Function Block (FB) is similar to a Standard FB, except that the function of the block, the order and definition of the block parameters, and the time required to execute the block are determined by an application-specific algorithm created by a programming tool. Flexible Function Blocks (FBs) 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.

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.

High Speed Ethernet (HSE) — High Speed Ethernet (HSE) is the Fieldbus Foundation's backbone network running at 100 Mbit/second.

HSE — High Speed Ethernet is the Fieldbus Foundation's backbone network running at 100 Mbit/second.

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 Segments to High Speed Ethernet (HSE) to create a larger network.

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.

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.

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.

Linking Device — A device used to interconnect H1 fieldbus segments to High Speed Ethernet (HSE) to create a larger network.

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 Objects — 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).

Master Backup — A field device containing Link Active Scheduler (LAS) functionality that can control communications on an H1 fieldbus Link.

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).

OLE — Object Linking and Embedding

OPC — OLE for Process Control

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.

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.

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.

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) — Standard Function Blocks (FBs) are 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.

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.

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 — The 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 describes three types of 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).