Orolia Spectracom VelaSync 1232, Руководство пользователя

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For more information on the TFOM value and Phase Error Limit, see "Configuring
the Oscillator" on page 153 .
Note: Changes made to the Holdover Timeout always take effect imme-
diately. If VelaSync is in Holdover and the Holdover timeout is changed to a
value that is less than the current time period that VelaSync has been in Hol-
dover Mode, the unit will immediately declare loss of synchronization.
What is the recommended setting for the Holdover Timeout period?
The factory default Holdover period is 2 hours (7200 seconds) . The value can be
increased to up to 5 years. During this time period, VelaSync will be useable by its NTP cli-
ents (or other consumers) after GNSS reception has been lost.
The length of time is really based on the type of oscillator installed in a unit, and what the
typical accuracy requirements are for the NTP clients. The longer it can run in Holdover
mode before it expires, the longer it can continue being a central time source for all of its cli-
ents. But the longer VelaSync runs in Holdover, the larger the offset to true UTC time will
become, because the undisciplined oscillator will drift over time:
The better the type of oscillator installed, the more stable it is while in Holdover and there-
fore, the less its time will drift away from true UTC time. This results in more accurate tim-
ing, over extended durations upon the loss of GPS input. For instance, a Rubidium
oscillator will maintain significantly better time over a longer Holdover duration than a
TCXO oscillator (TCXOs are considerably less stable than a Rb oscillator).
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CHAPTER
3
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VelaSync 1232 User Manual Rev. 4
3.3 Managing References