OS Function Block
March 2006
5-119
Cascade initialization is also required when the block
transitions from Auto to Cas mode. This action is
identical to that described for the PID block.
The required actions are summarized in table 5-46.
The BKCAL_OUT status shows limited high if an
increase in SP cannot be effectively passed on to
either output because the BKCAL_IN_n of both
outputs indicates that a move in the needed direction
is limited. Similarly, limited low is set if a decrease in
SP cannot be effectively passed on to either output.
The slope of the limited line(s) affects the limit
direction. BKCAL_OUT also shows limit status at the
X extremes X11 and X22.
Initialization is not automatic under all circumstance
because some situations have conflicting needs. In
general, when a control region is in trouble, the
upstream controller is limited so it will not drive further
into that region. When you want to move to the other
active region, you can put the upstream controller into
Man mode and move it, or you can drop the good
downstream block out of Cas mode for one evaluation
cycle and then restore Cas mode. This initializes the
upstream controller to the remaining good region of
control.
5
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