Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 180 of 265
b) If phases C or E need to keep right of way, ignore stage 1. Since phase B also
resides in stage 1, it does not matter if that phase has to keep right of way.
c) Stage 3 would service demands for phase D whereas stage 1 would not, so if
phase D is demanded, ignore stage 1.
d) If stage 2 has been suggested, it must have been due to a demand for phase D
which would force stage 1 to be ignored (see previous statement). Thus to reach
this statement, no stage has been suggested. Therefore, demands for either
phase A or B will suggest stage 1.
However, if phase C or phase E is a green-arrow, the move directly from stage 2
back to stage 1 may be prevented, see section 22.2.
If a stage has been suggested, the controller will move to that stage, otherwise it will
remain in stage 2.
When in Stage 3
Consider Stage 1 first…
a) If there are no demands for phases A and B, ignore stage 1 and check stage 2.
b) If phases D or E need to keep right of way, then ignore stage 1 (but remember if
there are demands for phases A and B) and check stage 2.
c) No previous stages have been checked so no demanded phases will be skipped.
d) No previous stages have been checked so a demand for either phase A or phase
B will suggest the move to stage 1.
Now consider Stage 2…
a) If there are no demands for phases B and C, ignore stage 2. Note that there can
be no demands for phase E since it is already at right of way.
b) If phase D needs to keep right of way, ignore stage 2. Since phase E also
resides in stage 2, it does not matter if that phase has to keep right of way.
c) Stage 1 would service demands for phases A and B. Phase B can be ignored
since it also appears in stage 2. However, if there is a demand for phase A,
ignore stage 2.
d) A demand for phase B can be serviced by both stages so if stage 1 has been
suggested, demands for phase B are ignored here. However, if stage 1 has not
been suggested*, a demand for phase B will suggest stage 2. Regardless, of
whether there is a demand for phase B, a demand for phase C will always
suggest the move from stage 3 to stage 2.
* If there is a demand for phase B, the only way that stage 1 can not be
suggested is if phases D and E need to keep right of way. If phase D needed to
keep right of way, it would also cause stage 2 to be ignored. However, if only
phase E is to keep right of way, a demand for phase B can cause the move from
stage 3 to 2 (assuming there are no demands for phase A).
If a stage has been suggested, the controller will move to that stage, otherwise it will
remain in stage 3.