Global Positioning System (Gps); S Ystem (Gps) - Motorola V186 - Cell Phone - GSM System Planner Manual

Clock Functions and Synchronization
The accuracy of other clocks is judged according to how "close" a clock is to a reference
clock (the stratum of the clock, the network latency to the clock, and the claimed
accuracy of the clock. The accuracy of NTP thus depends on the network environment.
Because NTP uses UDP packets, traffic congestion could temporarily prevent
synchronization, but the client can still self-adjust, based on its historic drift. Under good
conditions on a LAN without too many routers or other sources of network delay,
synchronization to within a few milliseconds is normal. Anything that adds latency, such
as hubs, switches, routers, or network traffic, will reduce this accuracy. The
synchronization accuracy on a WAN is typically within the range of 10-100 ms. For the
Internet/GPRS synchronization accuracy is unpredictable, so special attention is needed
when configuring a client to use public NTP servers. Testing with the ACE3600
connected with the Internet gains accuracy of 20-30ms, but theoretically it may be even
100ms.
NTP uses UTC time base (Coordinated Universal Time). UTC evolved from Greenwich
Mean Time (GMT). GMT is based on the earth's rotation, which is not constant enough
to be used for detailed time measurements. UTC is based on a standard second length
determined by the quantum phenomena. There is a difference of a few seconds between
the two (14seconds in 2006), so every several years add one more second (called leap
second) to UTC. This is built in NTP protocol.
To translate the UTC time into local time, user can configure Time zones and Daylight
Savings in RTU. Note however, that if setting NTP server to another stand alone
ACE3600, which has no time zone, both will operate with the same local time if no time
zone set. If that ACE3600 is connected to a GPS or to another NTP server then there is a
need to set a time zone.

Global Positioning System (GPS)

The ACE3600 system can use a GPS receiver precise time measurement application for
synchronization purposes, to synchronize the RTU with other SCADA systems.
The ACE3600 RTUs use GPS timing receivers equipped with a 1 Pulse per Second (PPS)
output. The receivers are connected to an RTU port. In case of a satellite failure, the
time is manufactured internally and the receiver indicates its inability to trace the
satellite.
The recommended GPS receiver is the Synergy Systems SynPaQ/E GPS Sensor with
M12+ Timing Receiver which must be purchased from a Synergy vendor. Along with
the timing receiver, a data/power cable and antenna should be purchased. For details on
connecting to the GPS receiver, see Appendix A: RS232/RS485 Adaptor Cables in the
ACE3600 STS Advanced Features manual.
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