IM 01C25R03-01E
3-1
3. ABOUT FIELDBUS
3.
ABOUT FIELDBUS
3.1 Outline
Fieldbus is a widely used bi-directional digital commu-
nication protocol for field devices that enable the
simultaneous output to many types of data to the
process control system.
The EJX910A Fieldbus communication type employs
the specification standardized by The Fieldbus Founda-
tion, and provides interoperability between Yokogawa
devices and those produced by other manufacturers.
Fieldbus comes with software consisting of five AI
function blocks that enable the flexible implementation
of systems.
For information on other features, engineering, design,
construction work, startup and maintenance of
Fieldbus, refer to “Fieldbus Technical Information” (TI
38K03A01-01E).
3.2 Internal Structure of EJX910A
The EJX910A contains two virtual field devices (VFD)
that share the following functions.
3.2.1 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).
3.2.2 Function Block VFD
(1)Resource block
• Manages the status of EJX910A hardware.
• Automatically informs the host of any detected
faults or other problems.
(2)SENSOR Transducer block
• Converts sensor output to pressure, static pressure,
and capsule temperature signals, and transfers to the
AI function blocks and flow transducer blok.
(3)FLOW Transducer block
• Accepts differential pressure, static pressure and
external temperature data from the transducer block,
calculates flow, and transfer to the AI function
block.
(4)LCD Transducer block
• Controls the display of the integral indicator.
(5)AI function block
• Condition raw data from the Transducer block.
• Output differential pressure, static pressure and
capsule temperature signals.
• Carry out scaling, damping and square root extrac-
tion.
(6)SC function block
• Converts the input signal value based on the
segment table function.
(7)IT function block
• Integrates one or two input signals and outputs the
result.
(8)IS function block
• Selects one of multiple input signals according to
the specified selection method and outputs the
signal.
(9)AR function block
• Performs ten types of calculations on a combination
of two main input signals and three auxiliary input
signals.
(10)PID function block
• Performs the PID control computation based on the
deviation of the measured value from the setpoint.
