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Manual
00809-0500-4881
•
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.
8.8.13
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.
8.8.14
Application examples
Temperature transmitter - situation
A temperature transmitter with a range of -328 to 842 °F (-200 to 450 °C).
Temperature transmitter - solution
Table 8-21
function block configuration.
Table 8-21: Analog Input Function Block Configuration for a Typical Temperature
Transmitter
Parameter
L_TYPE
XD_SCALE
OUT_SCALE
Rosemount OCX8800C
lists the appropriate configuration settings, and
F
Figure 8-7
illustrates the correct
Configured values
Direct
Not used
Not used
Fieldbus
™
OUNDATION
April 2023
133
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