ST750 GENERAL HANDBOOK
667/HB/33750/000 Page 29 Issue 6
Some timings considered to be safety timings can only be changed by a person at
the ST750 operating the write enable ‘level 3’ push button, e.g. minimum green,
intergreen, blackout timings, etc.
The default timings for the ST750 standard Pedestrian configurations are given in
their IC4 printouts (Special Instructions). These printouts also show the handset
commands that are used to change each of the timings. Some of these timings are
described in Section 3.
A summary of all the timings available within the ST750 Non-UK intersection
controller is contained in the ST900 General Handbook (see Section 1.3 for details).
It also shows their upper and lower limit values and, where applicable, the
configurable limits.
2.7.1 Tolerance
All timings, except CLF and Master Time Clock, are derived from the crystal
frequency which has a tolerance of 35 parts per million. An additional error, due to
random signals not being synchronised to the clock pulse, may add up to 200ms to
the time.
If the result of the above timings is required to change the signal lamps, a further
error may occur up to a maximum of 21ms.
The set-up accuracy of the real time clock and the accuracy of any offsets
calculated from it will be 1 second.
2.8 MASTER TIME CLOCK and CLF SUMMARY
• Master Time Clock
• Timing Sources – 50Hz or 60Hz Mains (automatically detected)
• Standby Timing – On board crystal and battery support programmable up
to 31 days. Accuracy of standby crystal oscillator is 35 parts per million.
• Programmable changeover to mains synchronisation.
• Facility for synchronising the real time clock or group timer from existing
UTC.
• Number of time switch settings – 64
• Number of time switch functions – 3
(a) Isolate controller
(b) Introduce a CLF plan
(c) Introduce time-switch events such as alternative maximum green
periods
• Cableless Link Facility
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