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Instruction Manual

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Instruction Manual
D103434X012
Blocks
November 2014
73
Appendix B BlocksB‐
Analog Input (AI) Function Block
The Analog Input (AI) function block (figure B‐1) 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 reports level status.
Figure B‐1. Analog Input (AI) Function Block
OUT_D
OUT
OUT
OUT_D
= THE BLOCK OUTPUT VALUE AND STATUS
= DISCRETE OUTPUT THAT SIGNALS A SELECTED
ALARM CONDITION
FIELDBUS‐FBUS_31A
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 [8]) reflects the process variable (PV [7]) value and status. In
Manual mode, OUT [8] may be set manually. The Manual mode is reflected on the output status. A discrete output
(OUT_D [37]) is provided to indicate whether a selected alarm condition is active. Alarm detection is based on the OUT
[8] value and user specified alarm limits. Figure B‐2 illustrates the internal components of the AI function block, and
table B‐5 lists the AI block parameters and their units of measure, descriptions, and index numbers.
Analog Input Block Modes
The AI function block supports three modes of operation as defined by the MODE_BLK [5] parameter:
D Manual (Man) The block output (OUT [8]) may be set manually.
D Automatic (Auto) OUT reflects the analog input measurement or the simulated value when simulation is enabled.
D Out of Service (OOS) The block is not processed. FIELD_VAL [19] and PV [7] are not updated and the OUT [8] status
is set to Bad: Out of Service. The BLOCK_ERR [6] parameter shows Out of Service. In this mode, you can make
changes to all configured parameters. The target mode of a block may be restricted to one or more of the
supported modes.
Alarm Detection
A block alarm will be generated whenever the BLOCK_ERR [6] has an error bit set. Block errors for the AI block are
defined in table B‐3.