Specifications
ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 262 of 265
The alternative is to add an intermediate stage to which the controller can ripple
change during the move from stage 2 to stage 3, so allowing it to terminate phases
A and B before phase F has actually appeared. Once phase F has appeared, the
controller can move to stage 5, bringing on phases C and E when any inter-green
times from A and B have expired.
STAGE 5STAGE 4STAGE 3STAGE 2STAGE 1
G
H
F
F
E
C
D
B
B
B
A
A
The following special conditioning generates the unlatched demands for the left-turn
green-arrow filter (phase F) and the intermediate stage (stage 4):
;in VA mode prevent stage 2 unless there is a demand for the ped
(MODE0 EQL <2>).NOT(LCPHG+UCPHG) = PRVST2
;when in stage 2 with A or B extending, demand stage 3 to switch off the
;ped and bring on the filter if there is a demand for main road phase E
STAGE2.(EXTAA+EXTAB).(LCPHE+UCPHE) = +UCST3
;if the controller is in or on the way to stage 3 and there is a demand
;for the main road (phase E) then demand the green arrow phase so it
;appears in stage 3 and also demand stage 4 to allow the controller to
;ripple change.
(NXTSTG0 EQL <3>).(LCPHE+UCPHE) := +UCPHF
*= +UCST4
The example below shows what happens if a gap appears on phases A and B three
seconds after phase G terminates and the controller started to move from stage 2 to
stage 3.
Time 0: Phase G’s minimum expires while
A or B is still busy and so the move
to stage 3 is started.
Time 3: A gap appears on A and B so the
controller can terminate phases A
and B and ripple change to stage 4
instead.
Time 6: When the inter-green from phase
G expires, phase F appears and
the controller is in stage 4.
Time 6.2: 200ms later phase F is no longer running its minimum green time and so
the controller can move to stage 5. However, since phase F is configured
as a filter green-arrow, it remains at green until its associated phase (E)
appears at green,
Time 9: Phase E appears when the inter-greens from phases A and B terminate.
3-4
6.2
630
G
F
E
B
4-5 Stage 52-3 4
(MIN F:0)
Stage 2
A
IGN A E:6
IGN G F:6
IGN B E:6
9