Emerson Rosemount OCX 8800 - Advanced Features; Application Information

Note
The AI block only supports the BAD if Limited option. Unsupported options are not grayed out; they
appear on the screen in the same manner as supported options.
7.8.12 Advanced features
The AI function block provided with the Fisher-Rosemount Fieldbus devices provides
added capability through the addition of the following parameters.
• ALARM_TYPE: Allows one or more of the process alarm conditions detected by the AI
function block to be used in setting its OUT_D parameter.
• OUT_D: Discrete output of the AI function block based on the detection of process
alarm condition(s). This parameter may be linked to other function blocks that
require a discrete input based on the detected alarm conditions.
• VAR_SCAN: Time period in seconds over which the variability index (VAR_INDEX) is
computed.
• VAR_INDEX: Process variability index measured as the integral of average absolute
error between PV and its mean value over the previous evaluation period. this index
is calculated as a percent of OUT span and is updated at the end of the time period
defined by VAR_SCAN.
7.8.13 Application information
The configuration of the AI function block and its associated output channels depends on
the specific application. A typical configuration for the AI block involves the following
parameters:
Channel
If the device supports more than one measurement, verify that the selected channel
contains the appropriate measurement or derived value.
L_TYPE
Select Direct when the measurement is already in the engineering units that you want for
the block output.
Select Indirect when you want to convert the measured variable into another, for example,
pressure into level or flow into energy.
Select Indirect Square Root when the block I/O parameter value represents a flow
measurement made using differential pressure and when square root extraction is not
performed by the transducer.
Scaling
XD_SCALE provides the range and units of the measurement, and OUT_SCALE provides the
range and engineering units of the output.
Foundation Fieldbus
142 OCX 8800