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Reference Manual
00809-0400-4728, Rev AA
June 2011
Rosemount 644
C-8
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 C-1 illustrates the internal components
of the AI function block, and Table C-3 lists the AI block parameters and their
units of measure, descriptions, and index numbers.
Figure C-1. AI Function Block
Analog
Measurement
Access
Analog
Meas.
CHANNEL
SIMULATE
OUT_SCALE
XD_SCALE
FIELD_VAL
L_TYPE
IO_OPTS
PV_FTIME
MODE
STATUS_OPTS
HI_HI_LIM
HI_LIM
LO_LO_LIM
LO_LIM
ALARM_HYS
ALARM_TYPE
OUT_D
OUT
PV
Convert
Cutoff Filter
Status
Calc.
Alarm
Detection
NOTES:
OUT = block output value and status.
OUT_D = discrete output that signals a selected alarm condition.
LOW_CUT