Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 10 Page 92 of 265
If the limit green override code is sent from the ATC computer during computer
stage control mode, the limit green watchdog timer is held reset.
In the event of a limit green watchdog timer timing out before its associated phase
green has terminated, the controller will then revert to the next highest priority mode
configured for which a request exists and the fault will be logged. If the current mode
at the time of failure is fixed time mode, the controller switches off the power to the
lamps.
6.6 Conditions of Appearance
If more than one phase is allocated to a stage, it may be required to make the
appearance of some of them conditional so that they will only appear if demanded.
The condition will apply in all the stages to which the phase is allocated.
There are four different types of appearance.
6.6.1 Appearance Type 0
This is the normal type of condition with the phase always appearing whenever its
associated stage runs. If more than one Type 0 phase is allocated to the stage they
will all appear regardless of which phase was demanded.
6.6.2 Appearance Type 1
The phase will only appear whenever its associated stage runs if a demand for the
phase is inserted before the start of the interstage. If the demand is inserted after
this point it will be stored and serviced later.
The normal use for this type of condition is for a pedestrian phase.
Normally the controller will continue to ignore these demands when considering the
next stage change and only consider the demand once the controller is at a stage
that no longer contains the phase. However, if there are no other demands present
or the PMV handset command has been set to ‘1’, the next stage decision making
process will consider the demand.
6.6.3 Appearance Type 2
The phase will only appear whenever its associated stage runs if the phase is
demanded, regardless of when the demand is inserted. There is no limit point for
when the demand may be inserted.
If the demand is inserted before the stage runs, the phase will appear at the start of
the stage. If the demand is inserted during the stage, the phase will appear
immediately. The appearance of the phase in both cases will be subject to any
relevant inter-green periods timing off.