Emerson 848T Appendix C FOUNDATION fieldbus Technology

00809-0100-4697, Rev EA

October 2011 Rosemount 848T

www.rosemount.com

Appendix C FOUNDATION™ fieldbus

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page C-1

Function Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page C-1

Device Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page C-3

Block Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page C-3

Network Communication . . . . . . . . . . . . . . . . . . . . . . . . . . page C-4

OVERVIEW FOUNDATION fieldbus is an all-digital, serial, two-way, multidrop

communication protocol that interconnects devices such as transmitters,

sensors, actuators, and valve controllers. Fieldbus is a Loca l 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 e nvironment is the base level group of di gital

networks and the hierarchy of plant networks.

The FOUNDATION 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 ter minations 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.

FOUNDATION 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.

FUNCTION BLOCKS Function blocks perform pro cess control functions, such as analog input (AI)

and analog output (AO) functions as well as proportional-integral-derivative

(PID) functions. The sta ndard function blocks provide a co mmon structure for

defining function block inputs, outputs, control parame ters, events, alarms,

and modes, and combining them into a proce ss 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.