Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 10 Page 79 of 265
If NO, add the demanded phases in this stage (or the stage itself if the stage
is demanded) to “Phases & stages to Get right of way”. Then try the next
stage in cyclic order (starting at Step 1).
5. Will additional demanded phases be serviced by this stage compared to the
previously “Suggested Stage”?
If YES, set “Suggested Stage” equal to this stage.
If NO, add the demanded phases in this stage (or the stage itself if the stage
is demanded) to “Phases & Stages to Get right of way”. Then try the next
stage in cyclic order (starting at Step 1).
At the end of the decision-making process, the “Suggested Stage” is either a new
stage other than the current stage, or it will have remained as the current stage.
If the suggested stage is other than the current stage, the controller then checks the
“Stage movement restriction” table that is appropriate to the mode, to see if it can
make the move. See section 24 Stage Movement Restrictions.
If the move from the current stage to the “Suggested Stage” is prohibited, the
controller will stay in the current stage until the decision-making process comes up
with a different “Suggested Stage” to move to.
If the move from the current stage to “Suggested Stage” is an Ignore move, the
controller will immediately return to the decision-making process. It will remove from
the equation the demanded phases which would have been served by the
previously “Suggested Stage” (so that the process does not come up with the same
“Suggested Stage” again), and then it will start again searching for a stage to move
to.
If the move from the current stage to the “Suggested Stage” has an alternative stage
move specified, the controller will move to the alternative stage (unless phases that
must keep right of way do not appear in that stage) and then restart the decision-
making process.
If the move from the current stage to the “Suggested Stage” is unrestricted, the
controller will move to the “Suggested Stage” and then restart the decision-making
process.
5.5.1 Effects of Modes other than VA on Stage Change Algorithm
In V.A. mode, the stage change algorithm is allowed to suggest a stage based on
the influences current at the time without any manipulating of those influences.
However, in other modes, namely CLF, UTC, Fixed Time, Priority, Part-Time,
Manual and Manual Step-On, the modes influence the outcome of the stage change
algorithm. This can be done by:
a) Applying stage/phase prevents,