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In my company we do have critical systems that require an accurate time.
As so, we have an NTP server appliance with an outdoor GPS antenna that receives the time from the GPS satellites.
My questions are:
Thanks,
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GPS accuracy is ~ 1 microsecond. NTP accuracy is ~ 100 milliseconds. GPS is more accurate than NTP and has less latency compared to NTP. clear sky, and after satellites are locked, the GPS master clock will send a signal every second to the slave clocks.
Atomic clocks are used onboard GPS satellites that orbit the Earth, but even they must be sent updates two times per day to correct the clocks' natural drift.
GPS devices typically need to receive signals from at least 7 or 8 satellites to calculate location to within about 10 meters. With fewer satellites contributing, the amount of uncertainty and inaccuracy increases.
Accuracy is better at night and in clear weather as the state of the atmosphere is more consistant and predictable. This is particularly the case if you are using WAAS or EGNOS to improve accuracy.
According to this reference, the time should be accurate to within 40 ns, which is much less than the time it would take to transmit that information to another system.
The reference also explains how GPS time might differ from UTC because of leap seconds that have been added since the deployment of GPS. The difference between the two is encoded in the GPS signal, but it is up to the GPS device to include the offset in its displayed time. Presumably an appliance that is dedicated to keeping time would do this part correctly.
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