Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 11 Page 132 of 265
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14.1 General Description
When a stream is in ‘part-time’ mode, all the signals in the stream are usually
extinguished allowing the traffic to flow normally. For example, it may be necessary
to control the traffic on a roundabout only during peak times, but not during the rest
of the day.
The normal method of switching between normal operation and part-time mode is by
means of the master time clock at specified times of the day.
An alternative method is by means of queue detectors. If a queue of traffic is
detected, normal traffic operations are introduced for a certain period, e.g. 20
minutes. At the end of this period, Part-time mode is re-introduced unless a queue is
still being detected, in which case the normal traffic operations will continue until the
queue is not detected for a certain length of time.
Alternative signal sequences, e.g. flashing amber for traffic phases during the night
may be configured if required (for Non UK Controllers ONLY). For alternative signal
sequences, see section 28.
Part-time mode may be introduced by the following methods.
a) Time switch event (see section 26.3) and/or queue detectors (see above)
b) Handset (SWS handset command)
c) Manual Panel switches (SW1, 2 or 3 as configured)
d) Red Lamp Faults (to flashing part-time state for non UK only)
e) Correspondence Faults (for non UK only)
It is a requirement in the UK that part-time mode may only be used if accompanied
by the Red Lamp Monitoring facility, see section 38.2.
14.2 Entering and Exiting Part-Time Mode
When part-time mode is requested (by time of day for example), the controller
moves immediately to its configured switch off stage, subject to any delays caused
by minimum greens or inter-greens timing off and also subject to any stage
movement restrictions.
When it reaches the switch off stage and all the minimum greens timers of all the
phases at right of way have expired, the signals are sent to their configured part-
time state via an optional ‘normal to part-time’ 3-step sequence.
Normally, no ‘normal to part-time’ sequence is defined and the part-time state is
blackout, so the signals are simply extinguished when all the minimum green times
expire in the switch off stage.