National Instruments FP-3000 - Manual (Page 53)

© National Instruments Corporation 4-1 FieldPoint FP-3000 User Manual
4
Block Reference
This chapter describes the function blocks and the parameters supported by
the FP-3000. For more information on blocks, refer to the F
OUNDATION
Fieldbus Overview document.
Block Overview
A block is a predefined software module that runs on an FP-3000 and acts
as a fundamental component of a control system. Each block has
parameters that can be adjusted to configure that part of the system. These
are referred to as contained parameters. In addition to contained
parameters, some blocks have I/O parameters. Input parameters receive
data from another block. Output parameters send data to another block.
I/O parameters of different blocks can be connected together to establish
communications between blocks. There are three types of blocks: function
blocks, transducer blocks, and the resource block.
Function Blocks
Function blocks implement the basic control algorithms that make up a
control strategy. The F
O U N D A TIO N Fieldbus specification defines a set of ten
fundamental (or elementary) function blocks and a set of nineteen
advanced function blocks. The function blocks encapsulate a significant
part of the control system behavior, thereby relieving a host (computer) of
such tasks. The F
O U N D A TIO N
Fieldbus specification defines the parameters
of each function block, how to make each parameter accessible to host
system, parameters for configuring function blocks, and I/O parameters
that can communicate with other function blocks in the system. For
example, an Analog Input (AI) function block has parameters to scale a
transducer value to engineering units. It also has alarm limits that can be
configured by a configurator or by an operator using a host application. The
AI block detects and reports process alarms such as
HI_HI , HI , LO , and
LO_LO . The Fieldbus specification does not specify the algorithm for
function blocks. For example, the specification does not define the actual
equations to use in a PID function block. However, it does define all the
parameters needed for configuration and operation of the PID, such as
RATE , GAIN , RESET , and MODE . The execution of function blocks and the