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Foundation Fieldbus Block Information
September 2018
B.3 Analog Input (AI) function block
The Analog Input (AI) function block processes field device measurements and makes them available to other function
blocks. The output value from the AI block is in engineering units and contains a status indicating the quality of the
measurement. The measuring device may have several measurements or derived values available in different channels. Use
the channel number to define the variable that the AI block processes.
The AI block supports alarming, signal scaling, signal filtering, signal status calculation, mode control, and simulation. In
Automatic mode, the block's output parameter (OUT) reflects the process variable (PV) value and status. In Manual mode,
OUT may be set manually. The Manual mode is reflected on the output status. A discrete output (OUT_D) is provided to
indicate whether a selected alarm condition is active. Alarm detection is based on the OUT value and user specified alarm
limits.
Figure B-1
illustrates the internal components of the AI function block, and
parameters and their units of measure, descriptions, and index numbers.
Figure B-1. AI Function Block
Analog
Measurement
Access
HI_HI_LIM
Analog
Meas.
LO_LO_LIM
CHANNEL
ALARM_HYS
Convert
SIMULATE
L_TYPE
FIELD_VAL
OUT_SCALE
XD_SCALE
OUT = block output value and status
51
ALARM_TYPE
HI_LIM
Alarm
Detection
LO_LIM
LOW_CUT
PV
Cutoff
Filter
PV_FTIME
IO_OPTS
STATUS_OPTS
OUT_D
OUT
Status
Calc.
MODE
OUT_D = discrete output that signals a selected alarm condition
Reference Manual
00809-0400-4728, Rev CA
Table B-3 on page 52
lists the AI block
Foundation Fieldbus Block Information
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