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
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 VelaSync is sub-
sequently rebooted or power cycled, time sync will be lost when VelaSync powers back-
up. The time will need to be set manually again in order for VelaSync to return to its fully
synchronized state. See
"The "User/User" Reference" on page 116
and
3.4
Managing the Oscillator
The purpose of the built-in oscillator is to provide VelaSync with an accurate and very
stable internal frequency source. This allows VelaSync 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 reference during normal operation,
in conjunction with an external time reference (for more information, see
Input Reference Priorities" on page 112
.)
152
CHAPTER
3
•
VelaSync User's Manual Rev. 3
3.4 Managing the Oscillator
Summary of Contents for VelaSync 1225
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