Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 179 of 265
When in Stage 1
Consider Stage 2…
a) If there are no demands for phases C and E, ignore stage 2 and check stage 3.
Note that there can be no demands for phase B since it is already at right of way.
Also note that the demand for phase C would usually come from a call/cancel
detector (see section 8).
b) If phase A is to keep right of way (due to extensions for example), ignore stage 2
(but remember if there are demands for phases C and E) and check stage 3.
Since phase B also resides in stage 2, it does not matter if this phase has to
keep right of way.
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 C or
phase E will suggest the move to stage 2.
Now consider Stage 3…
a) If there are no demands for phases D and E, ignore stage 3.
b) If phases A or B need to keep right of way, ignore stage 3.
c) Stage 2 would service the demands for phases C and E. Phase E can be ignored
since it also appears in stage 3. However, if there is a demand for phase C,
ignore stage 3.
d) A demand for phase E can be serviced by both stages so if stage 2 has been
suggested, its demands are ignored. Therefore, only a demand for phase D will
suggest stage 3.
Note that in this example it not possible for a demand for phase E to request
stage 3 from stage 1. This is because the demand will either cause stage 2 to be
suggested first (in which case stage 3 is no better) or neither stages can be
suggested (because phase A must keep right of way for example).
If a stage has been suggested, the controller will move to that stage, otherwise it will
remain in stage 1.
When in Stage 2
Consider Stage 3 first…
a) If there is no demand for phase D, ignore stage 3 and check stage 1. Note that
there can be no demands for phase E since it is already at right of way.
b) If phases B or C need to keep right of way, ignore stage 3 (but remember if there
is a demand for phase D) and check stage 1. Since phase E also resides in
stage 3, it does not matter if that phase has to keep right of way.
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 phase D will suggest
the move to stage 3.
Now consider Stage 1…
a) If there are no demands for phases A and B, ignore stage 1.