Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 260 of 265
phase delays affected’ is configured as required, rather than being left as the default
of ‘all ones’.
39.5.6 RLM Delays
The RLM facility will continue to function correctly along side ripple change, as long
as RLM delays are only configured between conflicting phases. The appearance of
phases will be delayed even if the vehicle phase actually terminated on a previous
stage change (unless the inter-green and RLM delay time has already expired).
RLM delays between non-conflicting phases (see section 38.2.2.2) will be
introduced regardless of how long ago the phase terminated.
39.5.7 Green Arrows
Left-turn green filter arrows may require an intermediate stage if the controller is
required to ripple from the left-turn only stage to the full green stage, see section
39.6.
39.5.8 UTC
If the controller can ripple from “1 to 2” to “2 to 3”, the controller can appear to be in
an interstage (from stage 1 to stage 3) for longer than normal. Therefore the
minimum and maximum limits used by the UTC Instation to check the interstage
times must be set-up to allow for the direct move from stage 1 to stage 3 as well as
the ripple change via stage 2. The maximum limit for the move from 1 to 3 needs to
allow for the summation of the interstage time from 1 to 2 plus the interstage time
from 2 to 3.
If the controller can make a number of ripple changes in succession before residing
in a stage and replying a stage confirm bit, the UTC Instation may report a fault
since the controller has been ‘stuck’ in an interstage for a long period of time. In this
case, either the Instation checking should be switched off if the controller is running
in isolation or phase confirms should be used instead of stage confirms.
Alternatively, dummy phases must be configured to force the controller to reside in
some of the stages for a minimum period before moving on.
39.6 Green Filter Arrows
Left-turn green filter arrows pose a particular problem for a ripple change. The
problem arises because, by default, the left-turn green filter arrow phase does not
appear in the ‘main road stage’, i.e. the stage which contains the associated three
aspect traffic signal, even though the traffic controlled by that signal moves in both
stages.
Consider the following example…