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Manual
00809-0500-4880
8.12.4
Block execution
The ISEL function block reads the values and statuses of as many as four inputs.
To specify which of the six available methods (algorithms) is used to select the
output, configure the selector type parameter (SEL_TYPE) as follows:
•
max selects the maximum value of the inputs.
•
min selects the minimum value of the inputs.
•
avg calcuates the average value of the inputs.
•
mid calculates the middle of three inputs or the average of the middle two
inputs if four inputs are defined.
•
1st Good selects the first available good input.
•
Hot Backup latches on the selected input and continues to use it until it is bad.
If DISABLE_N is active, the associated input is not used in the selected algorithm.
If OP_SELECT is set to a value between 1 and 4 , the selection type logic is
overridden, and the output value and status are set to the value and status of the
input selected by OP_SELECT.
SELECTED will have the number of the selected input unless the SEL_TYPE is
average, in which case it will have the number of inputs used to calculate its value.
8.12.5
Status handling
In Auto mode, OUT reflects the value and status quality of the selected input. If
the number of inputs with Good status is less than MIN_GOOD, the output status
will be BAD.
In Man mode, the OUT status high and low limits are set to indicate that the value
is constant, and the OUT status is always Good.
In the STATUS_OPTS parameter, the following options can be selected to control
the status handling:
•
Use Uncertain as Good: Sets the OUT status quality to Good when the selected
input status is Uncertain.
•
Uncertain if in Manual mode: The status of the Output is set to Uncertain when
the mode is set to Manual.
CAUTION
Set the system in Manual or Out of Service mode to set the Status option.
8.12.6
Application information
The input selector (ISEL) function block can be used to select the maximum
temperature input from four inputs and send it to a proportional/integral/
derivative (PID) function block to control a process water chiller
Rosemount OCX8800A
F
Fieldbus
™
OUNDATION
December 2022
(Figure
8-30) or it
209
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