Time Figure Of Merit (Tfom) - Spectracom VelaSync 1232 User Manual

4. Click Submit.
3.4.1.1

Time Figure of Merit (TFOM)

The TFOM reflects the
(such as GPS 1PPS) and the
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
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:
Reported TFOM Value
1
2
3
4
5
6
7
CHAPTER 3 • VelaSync User's Manual Rev. 3
Restart Tracking: Check this box, and click Submit if you want to
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
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).
estimated error
System 1PPS
TFOM to ETE conversion
Estimated Time Error (ETE)
<= 1 nsec
1 nsec < ETE <= 10 nsec
10 nsec < ETE <= 100 nsec
100 nsec < ETE <= 1 μsec
1 μsec < ETE <= 10 μsec
10 μsec < ETE <= 100 μsec
100 μsec < ETE <= 1 msec
3.4 Managing the Oscillator
will re-align the system 1PPS with the reference
range values between the
which is being aligned to the 1PPS. The estim-
manually
reference 1PPS
Estimated Time Error
155