Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 10 Page 87 of 265
Opposing phases that gain right of way at the same time will not
start each other’s
maximum green timers since the demands for those phases are disregarded while
they are at right of way.
Therefore, each phase is usually configured to ‘oppose’ all the other phases (in the
same stream) to guarantee that the maximum green timers for the phases at right of
way are started whenever there is a demand for a phase not at right of way.
6.5 Timing Periods
Each phase has its own timers to time periods such as its minimum green time, its
green extension time and its maximum green time. Each phase to phase transition
has its own inter-green timer.
The diagram below is intended to indicate the relationships between the various
timers in the controller:
PRIORITY
MODE
MINIMUM
GREEN
PRIORITY
MAX.
MAXIMUM
GREEN
MINIMUM
GREEN
INTER-
GREEN
PRIORITY PHASE ACTIVE
EXTEND
ALL RED
2ND
DELAY
1ST
DELAY
PRIORITY
REQUEST
GREEN EXTENSIONS
TAKE EFFECT HERE.
PRIORITY
DEMAND
INTERGREEN
INTERGREEN
INDEPENDENT
INTERGREEN
MINIMUM
GREEN
Figure 14 – General Timers
It shows the normal phase minimum green, inter-green and maximum green periods
which are described in this section, as well as showing their interaction with ‘priority’
mode (described in section 16) and the ‘extend all-red’ facility (section 10.2).
The following timing periods are set at the time of configuration but may be changed
using the handset commands in brackets.
6.5.1 Minimum Green (MIN)
When a phase gains ROW a minimum green period commences to time. For safety
reasons the phase cannot lose ROW until the minimum green has timed off.
Whatever mode of control is operative, the minimum green cannot be terminated
prematurely.