Honeywell Series A - 10.2 Standard Function Blocks

10. Appendix A
10.2. Standard Function Blocks
R400 Experion PKS Series A Fieldbus Interface Module User's Guide 381
July 2010 Honeywell
Physical Layer
Communication
Stack
User Application
Resource
Block
Function
Block
Transducer
Block
Fieldbus
Fieldbus Foundation
Defined Blocks
Figure 37 User Application (or Function Block Application Process) based
on blocks.
10.2 Standard Function Blocks
WARNING
The Fieldbus Foundation specifications do not clearly state the expectations
of fieldbus devices for handling Not-a-Number (NaN) values. This means that
some may behave as the user desires and others may not.
If you compute a data type float + status value that uses data structure (DS-
65), which includes all FOUNDATION Fieldbus inputs, outputs and some
contained parameters, a resulting NaN value passed outbound through the
FIM sets the status element to BAD and changes the value element from
NaN to 0.0 (zero). If you compute a data type float value, which includes
many contained values such as alarm trip points, set points or output limits,
gains, and filter time values, a resulting NaN value that is to be passed
outbound through the FIM will not be written and usually results in retention of