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 ref-
erence and start over (as if it was just acquired). This can be useful if there
is a large phase offset between reference 1PPS and system 1PPS, as it may
occur when going back into sync to the external reference after a long hold-
over. A
Restart Tracking
will re-align the 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 suit-
able to calibrate the oscillator. This function will delete the existing cal-
ibration data, and begin a new calibration process (not applicable for low
phase-noise Rubidium oscillators).
4.
Click Submit.
3.4.1.1
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 estim-
ated 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 value will be.
For example, TFOM 3 is reported when the estimated phase error is any value between
10 ns to less than 100 ns of the offset between the selected 1PPS reference and the sys-
tem’s 1PPS.
TFOM is VelaSync’s estimation of how accurately it is synchronized with its time and
1PPS reference inputs, based on several factors, known as the
Estimated Time Error
or ETE. The larger the TFOM value, the less accurate VelaSync believes it is aligned with
its 1PPS input that is used to perform disciplining. If this estimated error is too large, it
could adversely affect the performance of oscillator disciplining. The available TFOM
range is 1 through 15. You may refer to the following for the TFOM to ETE conversions:
Table 3-5:
TFOM to ETE conversion
Reported TFOM Value
Estimated Time Error (ETE)
1
<= 1 nsec
2
1 nsec < ETE <= 10 nsec
3
10 nsec < ETE <= 100 nsec
4
100 nsec < ETE <= 1
μ
sec
5
1
μ
sec < ETE <= 10
μ
sec
6
10
μ
sec < ETE <= 100
μ
sec
7
100
μ
sec < ETE <= 1 msec
3.4 Managing the Oscillator
CHAPTER
3
•
VelaSync User's Manual Rev. 3
155
Summary of Contents for VelaSync 1225
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