Rosemount 644

Reference Manual

00809-0400-4728, Rev AA June 2011

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-1illustrates the internal components of the AI function block, and Table C-3lists 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

ALARM_TYPE

HI_HI_LIM

 

HI_LIM

Alarm

LO_LO_LIM

Detection

LO_LIM

 

ALARM_HYS

 

LOW_CUT

OUT_D

 

Cutoff

Filter

PV

Status

Convert

 

 

 

 

 

 

Calc.

SIMULATE

L_TYPE

PV_FTIME

 

 

 

 

 

 

 

 

MODE

 

FIELD_VAL IO_OPTS

STATUS_OPTS

OUT_SCALE

XD_SCALE

NOTES:

OUT = block output value and status.

OUT_D = discrete output that signals a selected alarm condition.

OUT

C-8

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Emerson 644 manual Analog Input AI Function Block, Analog Measurement Access, Outd Cutoff Filter, Convert Calc