Yokogawa EJX930A - Manual (Page 22)

<3. About Fieldbus>
3-1
IM 01C25R03-01E
3. About Fieldbus
3.1 Outline
Fieldbus is a widely used bi-directional digital
communication protocol for field devices that
enable the simultaneous output to many types of
data to the process control system.
The EJX multivariable transmitter 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 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 EJX
Multivariable Transmitter
The EJX Multivariable transmitter 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 EJX 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
extraction.
(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.