Appendix D Foundation Fieldbus Communication; Function Block Overview; Function Blocks - Fisher FIELDVUEDVC6200f Instruction Manual

Instruction Manual
D103412X012
Appendix D F
DVC6200f digital valve controllers use
the control system. Fieldbus is an all digital, serial, two‐way communication system which interconnects "field"
equipment such as transmitters, digital valve controllers, and process controllers. Fieldbus is a local‐area network
(LAN) for instruments used in both process and manufacturing automation with built‐in capability to distribute the
control application across the network.

Function Block Overview

A fieldbus system is a distributed system composed of field devices and control and monitoring equipment integrated
into the physical environment of a plant or factory. 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 within the fieldbus device perform the various functions required for process control. Because each
system is different, the mix and configuration of functions are different. Therefore, the Fieldbus Foundation has
designed a range of function blocks, each addressing a different need: Analog Input Block (AI), Multiple Analog Input
(MAI), Discrete Input Block (DI), Manual Loader Block (ML), Bias/Gain Station Block (BG), Control Selector Block (CS), P,
PD Controller Block (PD), PID, PI, I Controller Block (PID), Ratio Station Block (RA), Analog Output Block (AO) and
Discrete Output Block (DO).
Function blocks perform process control functions, such as analog input (AI) and analog output (AO) functions as well
as proportional‐integral‐derivative (PID) functions. The standard function blocks provide a common structure for
defining function block inputs, outputs, control parameters, events, alarms, and modes, and combining them into a
process 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.
The Fieldbus Foundation has established the function blocks by defining a set of parameters used in all function blocks
called universal parameters. The Fieldbus Foundation has also defined a standard set of function block classes, such as
input, output, control, and calculation blocks. Each of these classes have a set of parameters established for it.
Additionally, they have published definitions for transducer blocks commonly used with standard function blocks.
Examples include temperature, pressure, level, and flow transducer blocks.
Fieldbus Foundation specifications and definitions allow vendors to add their own, extended parameters, as well as
their own algorithms. This approach permits extending function block definitions as new requirements are discovered
and as technology advances.
Each block has a tag name. Service personnel need only know the tag name of the block to access or change the
appropriate block parameters.
Input events may affect the operation of the algorithm. An execution control function regulates the receipt of input
events and the generation of output events during execution of the algorithm. Upon completion of the algorithm, the
data internal to the block is saved for use in the next execution, and the output data is snapped, releasing it for use by
other function blocks.
Once the inputs are snapped, the algorithm operates on them, generating outputs as it progresses. Algorithm
executions are controlled through the setting of internal parameters. Internal parameters do not appear as normal
input and output parameters. However, they may be accessed and modified remotely, as specified by the function
block.
Fieldbus
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Fieldbus to communicate with other fieldbus instruments and
DVC6200f Digital Valve Controller
F Fieldbus Communication
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