Table of Contents
If the status of OUT [7] is Bad, then the substatus will
be as follows:
D Out of Service if the Target mode is Out of
Service.
D Configuration Error with a BLOCK_ERR [6] of
Configuration Error if the Actual mode is Out of
Service.
D Otherwise a substatus of Non-Specific.
STATUS_OPTS Supported
In the STATUS_OPTS [10] parameter, you can select
from the following options to control the status
handling:
D Use Uncertain as Good—sets the OUT [7]
status to Good when the selected input status is
Uncertain.
D Uncertain if in Manual mode: sets the OUT [7]
status to Uncertain when the mode is Manual.
Note
The block mode must be Out of
Service to set STATUS_OPTS [10].
Input Selection
The ISEL function block reads the values and statuses
of as many as eight inputs (IN_1 [11], IN_2 [12], IN_3
[13], IN_4 [14], IN_5 [25], IN_6 [26], IN_7 [27], IN_8
[28]). To use any of the six selection algorithms to
select the output, OP_SELECT [22] must be 0. To
specify which algorithm to use, configure the selector
type parameter (SELECT_TYPE [19]) as follows:
D Maximum—selects the input with the highest
value from the inputs that are not bad and not
disabled.
D Minimum—selects the input with the lowest
value from the inputs that are not bad and not
disabled.
D Average—calculates the average value of the
inputs that are not bad and not disabled and provides
it as the output. For example, if the number used to
December 2009
ISEL Function Block
average (AVG_USE [33]) is 4 and the number of
connected inputs is 6, then the highest and lowest
values would be dropped prior to calculating the
average. If AVG_USE [33] is 2 and the number of
connected inputs is 7, then the two highest and lowest
values would be dropped prior to calculating the
average and the average would be based on the
middle three inputs.
D Middle—If the number of good usable inputs is
odd, then it selects the middle value. If the number of
good usable inputs is even, then it averages the
middle two values and selects status as worst of two.
If both inputs' limit status are not the same then it sets
limit status of Not Limited.
D First Good—selects the first input that is not bad
and not disabled, starting with IN_1 [11].
D Hot Spare—initially uses the input selected as
first good. If the selected input goes bad, the first good
selection is repeated. If the selected input remains
good, it stays selected. If the originally selected input
returns to good status the selection does not change.
Selection changes only if the currently selected input
goes bad.
Disabling Inputs
Use the parameters DISABLE_1 [15], DISABLE_2
[16], DISABLE_3 [17], DISABLE_4 [18], DISABLE_5
[29], DISABLE_6 [30], DISABLE_7 [31] and
DISABLE_8 [32] to disable the corresponding inputs.
An input that is disabled will not be used by any of the
selection algorithms.
The status of the disable parameter must be "Good,"
"Good_Cascade," or "Uncertain" with a
STATUS_OPTS [10] of "Use Uncertain as Good" in
order to be evaluated. If the status of the disable
parameter is Bad, its last usable value is maintained
and acted upon. If the device restarts, losing the last
usable value, the last usable value is set to disabled.
IN_1 through IN_8 and DISABLE_1 through
DISABLE_8 are non-volatile type parameters so if
they are Linked they will automatically have Bad status
until connections are re-established. If they are not
Linked, they will be restored with the previous value
from NVM across device restarts.
Direct Selection of Inputs
The parameter OP_SELECT [22] can be used to
select a particular input. If OP_SELECT [22] is
non-zero, the selection algorithm is bypassed and the
value of OP_SELECT [22] is interpreted as the input
number to select. If the OP_SELECT [22] value is
greater than the number of inputs, then the highest
input is selected. The status of OP_SELECT [22] must
4
4-107
- Quick Links:
- Travel Sensor
Hide quick links:
Chapters
Table of Contents
