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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 VersaSync 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:

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 μsec
5 1 μsec < ETE <= 10 μsec
6 10 μsec < ETE <= 100 μsec
7 100 μsec < ETE <= 1 msec
8 1 msec < ETE <= 10 msec
9 10 msec < ETE <= 100 msec
10 100 msec < ETE <= 1 sec
11 1 sec < ETE <= 10 sec
12 10 sec < ETE <= 100 sec
13 100 sec < ETE <= 1000 sec
14 1000 sec < ETE <= 10000 sec
15 ETE > 10000 sec