Time Figure Of Merit (Tfom) - Safran VersaSync User Manual

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
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
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 system's 1PPS.
TFOM is VersaSync'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 Ver-
saSync believes it is aligned with its 1PPS input that is used to perform dis-
ciplining. 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
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3 VersaSync User Manual Rev. 12
existing calibration data, and begin a new calibration process (not
applicable for low phase-noise Rubidium oscillators).
1PPS Phase
"Reference Monitoring: Phase" on
Always Restart Tracking After
ensure that every time the unit exits holdover, the discipline tracking
is restarted, to quickly align the oscillator. This may result in large tim-
ing jumps. It should be noted that this setting will only restart the
tracking once when using the Phase Error Limit, unless the unit re-
enters holdover.
4. Click Submit.
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
Validation: Turn ON Smart Reference Monitoring. See
Sync: When selected, this option will
3.4 Managing the Oscillator
page 183.
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