FOUNDATION

FIELDBUS

JUSTIN BABY

Contents

Introduction

Foundation Members

What is Fieldbus?

FF Components

FF Segment Topology

Comparison

Benefits

Applications

Introduction

Established by International Society of

Automation

Goal: A single international, interoperable

fieldbus standard.

Not-for-profit corporation

Fieldbus technology is based on the work of the

IEC and ISA. IEC std. for FF – IEC 61158

Fieldbus Foundation has nearly 100 member

companies, which supply over 90% of the

worlds instrumentation and control products.

Foundation Members

What is Fieldbus?

Fieldbus is a digital, serial two-way, multi-drop

communication link among intelligent field

devices and automation systems.

It is an open architecture, developed and

administered by the Fieldbus Foundation.

H1 (31.25kbps)

HSE (High Speed Ethernet)

<1930’s – Direct connected devices

1940’s – Pneumatic signal transmission

1950’s – 10-50/4-20mA replacing 3-15psi

1970’s – Process computers appear (PLCs)

1980’s – DCS implemented

1990’s – First FF systems

2000’s – Fieldbus crosses “chasm”

FF Components

Fieldbus cable Types

FF Segment Topology

Point-to-point

Chicken-foot (Tree) Topology

Daisy chain

Spur Topology

TrunkSpur

Comparison

Benefits

1. Wiring/Installation Savings

2. Control Anywhere

3. More Available Data

4. Enhanced User Interface

5. Interoperability

Fieldbus Communication

One of the most important aspects of

FOUNDATION fieldbus is its ability to collect and

deliver vast amounts of information - not only

process variables and control signals, but other

types of instrument and process data as well.

Physical Layer

Translating messages into physical signals

on the wire - and vice versa

The physical layer also provides the

common electrical interface for all

FOUNDATION fieldbus devices.

The FOUNDATION fieldbus physical layer is

defined by approved standards (IEC

61158-2 and ANSI/ISA 50.02, part 2).

Data Link & Application Layers

It combines several technologies that together

control transmission of data on the fieldbus.

The data link and applications layers provide

a standard way of "packaging" the data, as

well as managing the schedule for

communication and function-block

execution.

They enable process control while providing

standardization and interoperability.

User Layer

It enables user to interact with the other layers

and with other applications.

The user layer contains

Resource blocks - describes characteristics of the

fieldbus device such as device name, mfr. and

serial number, etc.

Transducer blocks - used to configure devices

Function blocks - The Control System Strategy is built

using Function Blocks. Input and output parameters

of Function Blocks can be linked over the fieldbus.

Device descriptions enable the host system to

interact with and understand these blocks without

custom programming.

Important Definitions

Scheduled Communications

All devices and function blocks on a

FOUNDATION fieldbus segment execute and

communicate process control information on

a regular, repeating cycle.

Timing for this type of communication is

determined by a master schedule in a Link

Active Scheduler, which is a function residing

in the host system or one of the devices on

the segment.

Application Clock

Every device on a FOUNDATION fieldbus

segment shares the same time.

A system management function called the

application clock periodically broadcasts the

time - either local time or Universal

Coordinated Time -- to all devices. Each

device uses an internal clock to keep time

between these synchronization broadcasts.

Link Active Scheduler

The link active scheduler (LAS) function

maintains the central, deterministic

schedule for communication between

devices on a segment.

It improves overall communication

reliability by compelling each device to

transmit cyclic data when it's scheduled

to do so.

Device Address Assignment

FOUNDATION fieldbus carries signals to and from

several devices over the same cable. To identify

which information is associated with which

device, each device is assigned an address.

Depending on the communication protocol,

addresses can be assigned in several ways, from

dip switches or off-line addressing to automatic

online assignment.

Online addressing helps avoid problems such as

duplicate devices with the same address, but by

itself does not guarantee there are no addressing

errors.

Signals

Devices on a Fieldbus segment transmit digital

signals to each other over the same wires that

power the devices.

A DC bus voltage (nominally 24V but can befrom 9‐32VDC) is supplied to the devices on the

segment by the Fieldbus Power Supply. A

Fieldbus device draws a constant amount of

current when not transmitting. To transmit

information, the device varies the amount of

current it draws from the segment to create a

signal “riding” on the 24VDC.

Digital data is sent on the Fieldbus at a rate of

31.25 Kbits/second.

Fieldbus Signal

Fieldbus Power Supply

Isolator – To improve noise immunity

Power Conditioner – Like a one way valve

Current Limiter – Prevent damage from

short-circuit or over-load conditions

Applications

Refining

Petrochemicals

Power generation

Food & beverage

Pharmaceuticals

Nuclear Applications

Zone-1 (Intrinsically Safe)

Zone-2 (Non - Incendive)

References

Fieldbus Installation in a DeltaV™ Digital

Automation System – Emerson Process

Management

QGX/20/00/IN/TS/NA/040, Rev-E2 –

Foundation Fieldbus Design Specification

www.wikipedia.com/foundation_fielbus