Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 184 of 265
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There are three methods of fixed time working:
 Fixed Time mode (FT)
 Fixed Time to Current Maximums (FTCM)
 Fixed Vehicle Period (FVP) mode on a stand-alone pedestrian stream.
23.1 Fixed Time Mode
Fixed Time Mode is implemented:
 when ‘Fixed Time’ is selected on the mode select buttons subject to mode priority
 by default, if there is no higher priority mode is active and no VA
During Fixed Time mode, the controller cycles round a pre-programmed sequence
of stages disregarding local demands and extensions. The stage durations are
exclusive to the Fixed Time mode and do not include inter-green timings or phase
delays that will be implemented as during Vehicle Actuated mode. The stage
duration can be changed via the handset but the stage sequence cannot. Not all
stages need be included in the sequence.
Phases that appear conditionally will always appear in their corresponding stages,
i.e. there will be permanent requests.
The range of the timing period for the stage duration is 0 to 255 seconds in 1-
second steps. There is only one set of timings. The programmed values may be
changed via the handset using the FIX command.
Any all-red extension periods are automatically extended up to the maximum value
to ensure safe operation.
When Selected Fixed Time mode ceases, demands may be automatically inserted
for selected non-running phases. These demands are normally inserted to ensure
no vehicles are trapped against a red light, unless otherwise requested by a
customer.
23.2 Fixed Time to Current Maximums
If Fixed Time to Current Maximums has been selected via configuration set up,
when FIXED TIME is selected this mode is entered subject to mode priority. The
controller will then operate to VA mode strategy and not to a pre-programmed
sequence as in Fixed Time mode, but with Permanent Demands and Extensions.
This method of operation has been created so that the following are possible:
- Phases which appear conditionally may be excluded from having
permanent demands and still rely on local demands for their
appearance, e.g. pedestrian phases.
- Any set of maximum green timings may be introduced giving eight sets
of fixed times switched by the master time clock.