Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 177 of 265
2. The use of the ‘Hold’ and ‘Prevent’ group influences should be avoided if
possible, but if not their use, i.e. the group time and Group position within the
plan, must be considered carefully.
The “GO VA” influence should not be used at all, as this will nearly always cause
disruption to the Synchronisation of Controller and Plan, even when used in CLF
in general.
3. Group times should be a minimum of the maximum inter-green between the
stage associated with the group influence and the stage associated with the
previous group influence. Plus the longest minimum green of the phases
appearing in the stage associated with the group. Longer Group times will
obviously aid synchronisation.
For example, consider if Group 0 is an immediate move to stage 1 and Group 1
is an immediate move to stage 2. The minimum time for group 1 should be longer
than the longest phase inter-green between Stage 1 and 2 and longest minimum
green of phases appearing in Stage 2.
21.9 Synchronisation of Cableless Linking Equipment
Synchronisation of Cableless Linking Equipment (i.e. maintaining required offsets
for the running plan) in adjacent controllers can be achieved either by the UTC
computer or by operators locally adjusting the real time when no link to the UTC
computer exists, or is not required.
The UTC computer can correct small errors in the real time clock by sending the
TS1 command at one of the following minute boundaries past an hour 8, 18, 28, 38,
48, 58. This would correct the Real Time Clock if the error were no more than 29
seconds (see section 15.3.23).
The UTC computer can set the real time in the controller to a pre-programmed
system time and the computer will send the TS control signal at the time which is
programmed (see section 15.3.20).
In the absence of the computer system, adjacent controllers can easily and
accurately be synchronised by local operators setting the controller RTC to ‘system
time’ using one controller as the master reference. No other adjustments are
necessary to synchronise the controller to adjacent controllers running the current
local co-ordinated mode system plan.
(See Section 7 of the ST900 Controller Handset Handbook for details of
synchronisation procedure.)