Foundation fieldbus, 1 about foundation fieldbus, 1-1 outline – Yokogawa DO202 2-Wire Dissolved Oxygen Analyzer User Manual

Page 6: 1-2 internal structure of exa, 1-2-1 system/network management vfd, 1-2-2 function block vfd, 1-3 logical structure of each block, Foundation fieldbus -1, 1 about foundation fieldbus -1, 1-1 outline -1

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IM 12A00A01-61E

Foundation Fieldbus 3-1

3. FOUNdATION FIELdBUS

3-1 About Foundation Fieldbus

3-1-1 Outline

Fieldbus is a bi-directional digital communication protocol for field devices, which offers an advance-
ment implementation technologies for process control systems and is widely employed by numerous
field devices.

EXA Series Fieldbus communication type employs the specification standardized by The Fieldbus
Foundation, and provides interoperability between Yokogawa devices and those produced by other
manufacturers. Fieldbus comes with software consisting of three AI function blocks, providing the
means to implement flexible instrumentation system.

For information on other features, engineering, design, construction work, startup and maintenance of
Fieldbus, refer to http://www.yokogawa.com/fbs/fbs-index.htm.

3-1-2 Internal Structure of EXA

The EXA contains two virtual field devices (VFD) that share the following functions.

3-1-2-1 System/network Management vFd

• Sets node addresses and Physical Device tags (PD Tag) necessary for communication
• Controls the execution of function blocks
• Manages operation parameters and communication resources (Virtual Communication Relationship:

VCR)

3-1-2-2 Function Block vFd

(1) resource block

• Manages the status of EXA hardware
• Automatically informs the host of any detected

faults or other problems

(2) Transducer block

• Converts sensor output to process values and

transfers to AI function block by channels

(3) AI1, AI2, AI3 function block

• Conditions raw data from the Transducer block
• Outputs conditioned process values
• Carries out scaling, damping and square root

extraction

3-1-3 Logical Structure of Each Block

Setting of various parameters, node addresses, and
PD Tags shown in Figure 3.1 is required before
starting operation.

System/network management VFD

Function block VFD

PD Tag

Sensor

input

Resource block

Block tag

Parameters

Communication

parameters

VCR

Node address

Function block

execution schedule

AI function

block

AI function

block

Output

AI function

block

Block tag

OUT

Parameters

Transducer

block

Block tag

Parameters

Sensor

Figure 3.1 Logical Structure of Each Block

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