Rockwell Automation PLC-5 Fieldbus Solutions for Integrated Architecture User Manual - Manual (Page 52)

Publication 1757-UM006A-EN-P - May 2002
2-8 Integrating Fieldbus into Rockwell Automation Logix System
Figure 2.3 shows a simplified functional diagram of how the output
from an Analog Input function block in a fieldbus compliant
transmitter is integrated with a PID function block in a Control Module
that is assigned and loaded to the CEE in the Control Processor
Module (CPM).
Figure 2.3 Integration of fieldbus device analog input signal with ProcessLogix
control strategy
Fieldbus Analog Input data manipulation
When the OUT from the fieldbus analog input function block is wired
to the PV input for a PID function block, the Control Builder creates a
CEE input agent to handle the analog input from the fieldbus block.
The block-like input agent maps the data structure (DS-65) of the
OUT parameter to the ProcessLogix PV with status parameter. It
interprets the value portion in fieldbus terms and converts it to
ProcessLogix representation. The floating-point representation is
identical, in most cases, but the fieldbus +/-infinity value must be
converted to a ProcessLogix representation.
If the fieldbus status byte indicates “BAD”, the value must be
converted to Not a Number (NaN) for ProcessLogix representation.
CM
CPM/CEE
FIM
Fieldbus
Device
FIM
Analog
Input
Transducer
PID
AOC
OUT
PV
OP
OP
AOC = Analog Output Channel
CEE = Control Execution Environment
FIM = Fieldbus Interface Module
OP = Output
PID = Proportional, Integral, Derivative
CM = Control Module
CPM = Control Processor Module
PV = Process Variable