Glossary List_2

erm	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)	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.
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).