Time Figure Of Merit (Tfom) - Safran SecureSync 2400 User Manual

3.5.2.1

Time Figure of Merit (TFOM)

The TFOM reflects the estimated error range values between the reference 1PPS
(such as GPS 1PPS) and the System 1PPS which is being aligned to the 1PPS. The
estimated error is referred to as the 1PPS Phase error. TFOM values are ranges of
these phase errors. The larger the phase error estimate, the larger the TFOM
CHAPTER •
3 SecureSync 2400 User Manual Rev. 5.2
Maximum TFOM for
also "Time Figure of Merit (TFOM)"
disciplining will still be attempted against the selected reference to
improve the TFOM. If the condition persists, the system will transition
to holdover, and eventually out of sync. When disciplining is per-
formed such that TFOM is no longer greater than max TFOM, the sys-
tem will transition back into sync.
Holdover Timeout(s): The default is 7200 s (= 2 hours).
For more information on holdover timeouts, see
lengths in seconds" on
over, see "What is "Holdover Timeout"?" on
Phase Error
(valid for +/-) for the Phase Error between an external 1PPS reference
and the System 1PPS will cause the disciplining tracking to restart
automatically (after a few minutes delay) if that limit is exceeded. This
will help to quickly re-align the System 1PPS with a reference.
When using a Host Reference as a primary or backup reference, for
improved performance it is recommended to set the phase error limit
for NTP to a suggested value of 100000 ns (= 100 μ second). Adjust
this value as needed, based on your accuracy requirements.
Restart Tracking: Check this box, and click Submit if you want to
manually restart disciplining tracking.
This option causes the disciplining algorithm to stop tracking the
input reference and start over (as if it was just acquired). This can be
useful if there is a large phase offset between reference 1PPS and sys-
tem 1PPS, as it may occur when going back into sync to the external
reference after a long holdover. A
system 1PPS with the reference 1PPS very quickly, but may cause the
1PPS output to jump.
Recalibrate: In rare cases, existing calibration data may no longer be
suitable to calibrate the oscillator. This function will delete the exist-
ing calibration data, and begin a new calibration process (not applic-
able for low phase-noise Rubidium oscillators).
4. Click Submit.
Sync: When TFOM (Time Figure of Merit, see
page 249. For additional information on hold-
Limit: [Default=0 (disables this feature)]. Setting a Limit
3.5 Managing the Oscillator
below) is greater than Max TFOM,
"Typical Holdover
page 247.
Restart Tracking will re-align the
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