Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 174 of 265
21.6.2 Using Plan Offset Times (Base Time CLF Only)
The offset between the controllers is achieved by specifying ‘offset’ times at each
controller. Note that ‘offset’ times are only available with the Base Time CLF system.
If this system is used, all the plans at each controller can request the main road to
appear at green at time ‘0’ within the cycle time for example. Therefore, the
controllers would be configured as follows:
Plan 0 A B C Plan 1 A B C
Group 0
(Main Road)
0 0 0
Group 0
(Main Road)
0 0 0
Group 1
(Side Road)
40 45 35
Group 1
(Side Road)
30 25 25
Cycle Time 60 60 60 Cycle Time 45 45 45
Offset Time 35 20 0 Offset Time 0 19 46*
* See Note 2
Thus, when all the controllers start plan 0 at 8:30:00 in the morning:
 The plan at controller ‘C’ has an offset time of 0 seconds configured and so
starts at time 0 within its cycle time as normal (see note 1).
 The plan at controller ‘B’ has an offset time of 20 seconds configured and so
starts 20 seconds behind, i.e. starts at time ‘40’ in the cycle and reaches time ‘0’
20 seconds later.
 The plan at controller ‘A’ has an offset time of 35 seconds configured and so
starts 35 seconds behind, i.e. starts at time ‘25’ in the cycle and reaches time ‘0’
in 35 seconds.
Similarly for the evening peak, all the controllers start plan 1 at 16:50:00, but the
plan at controller ‘B’ starts 19 seconds behind the plan at controller ‘A’, and the plan
at controller ‘C’ starts 46 seconds behind the plan at controller ‘A’.
Note 1
The above example for plan 0 can ignore the base time and assume that the plan
starts at time ‘0’ to aid clarity. This is because the plan’s 60-second cycle time
repeats every 60 seconds and thus returns to time 0 on each minute boundary of the
real time clock, including at the start time of 08:30:00 (assuming the base time is set
to 02:00:00 for example).
However, for plan 1, its 45-second cycle time means that even though the offset
time for the ‘A’ is zero, it still starts part way through the cycle. This is because the
start time of 16:10:00 minus the base time (assumed to be 02:00:00) divided by 45
seconds, equals 1133 cycles and a remainder 15 of seconds. Therefore, the plan at
starts at time ‘15’ in the cycle.
Note 2
The offset time for plan 1 at controller ‘C’ is configured as ‘46’ seconds even though
the cycle time for the plan is only 45 seconds. The controller automatically adjusts