Safran SecureSync 2400 - Managing the Oscillator

Note: Due to Leap Seconds that are periodically inserted into the
UTC and Local timescales, it is not normally recommended to exceed
30 days of Holdover without an external reference that can supply
Leap Second information being applied (such as GNSS).
Configuring a Holdover value exceeding 30 days could result in a one-second
time error in the UTC or Local timescales until an external reference (GNSS or
IRIG input) is restored or a manually configured Leap Second is asserted by a
user (leap seconds do not affect the GPS and TAI time scales).
If no external references (such as GNSS or IRIG) are available when a Leap
Second is scheduled to occur, manual Leap Seconds can also be applied to the
UTC or Local time base; see "Leap Seconds" on page196.
If the Holdover Timeout has expired, do I need to reset the clock once
GPS becomes available again?
No, the Holdover timer is automatically reset as soon as at least one reference
has been restored/returned for at least one second. If GPS is restored and then
lost again moments later, the Holdover timer starts again with its full value. If its
set to one week in this case, it then gets another week of Holdover operation
before NTP goes to Stratum 16 (if GPS remained unavailable for the entire week).
Holdover mode and the User/User reference
If the only available input reference is a manually set User time, and SecureSync is
subsequently rebooted or power cycled, time sync will be lost when SecureSync
powers back- up. The time will need to be set manually again in order for
SecureSync to return to its fully synchronized state. See "The "User/User" Refer-
ence" on page210 and "Manually Setting the Time" on page191 for more inform-
ation.
3.5 Managing the Oscillator
The purpose of the built-in oscillator is to provide SecureSync with an accurate
and very stable internal frequency source. This allows SecureSync to go into a
holdover mode in the event that external time or frequency references are lost or
become invalid. However, the oscillator can also be used as a legitimate 1PPS ref-
erence during normal operation, in conjunction with an external time reference
(for more information, see "Configuring Input Reference Priorities" on page205.)
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CHAPTER 3 • SecureSync 2400 User Manual Rev. 5.2
3.5 Managing the Oscillator