Emerson Rosemount 848T, Reference Manual, Page: 99 / 136

Reference Manual
00809-0100-4697, Rev GA
Appendix C: F
OUNDATION
Fieldbus Technology
November 2014
89 F
OUNDATION
Fieldbus Technology
Appendix C F
OUNDATION
™
fieldbus
Technology
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 89
Function blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 89
Device descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 90
Block operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 91
Network communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 91
C.1 Overview
F
OUNDATION
fieldbus is an all-digital, serial, two-way, multi-drop communication protocol that
interconnects devices such as transmitters, sensors, actuators, and valve controllers. Fieldbus is
a Local Area Network (LAN) for instruments that are used in both process and manufacturing
automation, having the built-in capability to distribute the control applications across the
network. The fieldbus environment is the base level group of digital networks and the hierarchy
of plant networks.
The F
OUNDATION
fieldbus retains the desirable features of the 4–20 mA analog system, including
standardized physical interface to the wire, bus-powered devices on a single pair of wires, and
intrinsic safety options. It also enables the following capabilities:

Increased capabilities due to full digital communication.

Reduced wiring and wire terminations due to multiple devices on one pair of wires.

Increased supplier selection due to interoperability

Reduced loading on control room equipment due to the distribution of some control
and input/output functions to field devices.
F
OUNDATION
fieldbus devices work together to provide I/O and control for automated processes
and operations. The Fieldbus Foundation provides a framework for describing these systems as
a collection of physical devices interconnected by a fieldbus network. One of the ways that the
physical devices are used is to perform their portion of the total system operation by
implementing one or more function blocks.
C.2 Function blocks
Function blocks perform process control functions, such as analog input (AI) and analog output
(AO) functions as well as proportional-integral-derivative (PID) functions. The standard function
blocks provide a common structure for defining function block inputs, outputs, control
parameters, events, alarms, and modes, and combining them into a process that can be
implemented within a single device or over the fieldbus network. This simplifies the
identification of characteristics that are common to function blocks.
The Fieldbus Foundation has established the function blocks by defining a small set of
parameters used in all function blocks called universal parameters. The F
OUNDATION
has also
defined a standard set of function block classes, such as input, output, control, and calculation
blocks. Each of these classes has a small set of parameters established for it. They have also
published definitions for transducer blocks commonly used with standard function blocks.
Examples include temperature, pressure, level, and flow transducer blocks.