Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 172 of 265
If the current plan does not have an exit time configured, but the new plan has an
entry time configured, the current plan continues until the new plan reaches its entry
time and takes control.
The range for the (PLE) entry time and the (PLX) exit time is 0 to ‘the cycle time
minus 1’, in 1-second steps. A value of 255 indicates that no entry/exit time is
required.
21.5 Non Base Time CLF System
The non-base time CLF system is a configurable alternative to the base time CLF
system.
This system does not use a ‘base time’. When a CLF plan is requested to start, it
starts at the beginning, i.e. at time ’0’, of its CLF cycle.
Therefore the time that a plan is requested to start (i.e. the time in the controller’s
timetable) is critical to ensure that the CLF plan is synchronised with other
controllers in the same area. Also see section 21.6.
21.6 Offset Times and Linked Installations
21.6.1 Introduction to Offset Times
The CLF facility allows a number of controllers in an area to be synchronised
allowing the traffic flowing between them to move more freely. Consider the
following simple example:
The figures below show a simple linked installation covering three intersections on a
main road into a city. The CLF facility is used at the controllers at each of the three
intersections ‘A’, ‘B’ and ‘C’.
Note that the plan start times are shown for a non-base time CLF system option
described in section 21.6.3. For all other ways of working (as described in the rest of
section 21.6), all the controllers will start running the plans at 08.30.00 and
16.15.00.
A 20 Secs15 Secs
08:30:0008:30:35 08:30:20Plan Start:
CB
CITY
CENTRE
40 Secs
20 Secs
Controller Timings:
(60-second cycle time)
45 Secs
15 Secs
35 Secs
25 Secs
Figure 31 – Simple Linked Installation (Morning Peak – Plan 0)