Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 10 Page 75 of 265
4.4.1 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, which may be up to a maximum of 21mS.
The set-up accuracy of the real time clock and offsets calculated from it will be 1
second.
4.5 Modes of Operation
 Vehicle actuated (SDE/SA can be added to VA)
 Timetable selected fixed time plans either Cableless linked or in isolation.
 Central computer controlled in a traffic control system.
 MOVA (using the UTC external or serial semi-integral interface)
 Fixed time
 Hurry call
 Manual
 Parallel stage streaming
 Priority
 Part time lamps off
 Part time lamps flashing, e.g. flashing vehicle ambers
 Stand-alone pedestrian stream ‘VA’ (with pre-timed maximum option)
 Stand-alone pedestrian stream ‘Fixed Vehicle Period’
4.6 Master Time Clock Summary
 Master Time Clock
 Timing Sources - 50Hz or 60Hz Mains (automatically detected)
 Option for GPS (Global Positioning System) unit from which the controller
continually checks and updates its clock. Refer to section 25.6 on page
192 for more information on this option.
 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.
 Facilities for synchronising the real time clock and group timer from
existing U.T.C.
 Number of time switch settings - 64
 Number of time switch functions - 3
a) Isolate controller
b) Introduce a CLF plan
c) Introduce events, such as alternative maximum greens