Analog Input (Ai) Function Block - Emerson Rosemount 848T FOUNDATION Reference Manual

Reference Manual
00809-0100-4697, Rev GA
Appendix D
Analog Input (AI) function block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 97
Multiple analog input (MAI) function block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 106
Input selector function block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 113
D.1

Analog Input (AI) function block

AI
Out = The block output value and status
Out_D = Discrete output that signals a selected alarm condition
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. The block execution time is 30 ms.
Table D-1. Analog Input Function Block Parameters
Number
01
02
03
04
Function Blocks
Function Blocks
OUT_D
OUT
Parameter Units
ST_REV None
TAG_DESC None
STRATEGY None
ALERT_KEY None
Appendix D: Function Blocks
Description
The revision level of the static data associated with the
function block. The revision value will be incremented
each time a static parameter value in the block is
changed.
The user description of the intended application of the
block.
The strategy field can be used to identify a grouping
of blocks. This data is not checked or processed by the
block.
The identification number of the plant unit. This
information may be used in the host for sorting
alarms, etc.
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