Instrumentation & Measurement Magazine 23-5 - 38
Fig. 3. Time scale frequency of traditional exponential filtering.
Fig. 2. Frequencies of each hydrogen maser. a) H226 frequency data; b) H339
frequency data; c) H341 frequency data.
of frequency are 15.3552, 28.3080 and 33.7944 ns/d. The initial
values of frequency drift are 2.67e-16, 5.33e-16 and 2.00e-15
ns/d, respectively. Fig. 2 displays the frequency data of each
hydrogen maser. Fig. 3 shows the time scale of all hydrogen
masers calculated by an exponential filtering method.
From Fig. 2 and Fig. 3, it is obvious that the time scale frequency fluctuation of traditional exponential filtering is less
than that of any single hydrogen maser. In order to characterize the frequency stability quantitatively, Allan deviations
are calculated. The Allan deviation data of the time scales of
the masers and paper clock are shown in Table 1. Reference
is given to the local atomic time TA(NTSC). The deviation
between the time scale of the hydrogen maser ensemble calculated by exponential filtering method relative to TA (NTSC)
within the three month interval is less than 20 ns, the frequency
stability of 1h can reach 8.59e-15, and the frequency stability of
5d can reach 4e-15.
Fig. 4 shows the time scale of the paper clock calculated by
a traditional exponential filtering method. The deviation between the calculated time scale relative to TA(NTSC) is within
20 ns in three months. At the same time, we find that there is
a clear trend in this data, and with the passage of time, the
deviation from TA(NTSC) is increasing. This is because the
frequency drift parameters of each clock in the period of this
month are only quadratically fitted, which is fixed. In fact,
the frequency drift parameters of atomic clocks change in 92
days, and the fixed frequency drift parameters are obviously
inconsistent with the actual situation. This leads to inaccurate estimation of frequency drift parameters, which will be
brought into the time scale of the paper clock and the results
present the above trend. Thus, it is also very important to estimate the frequency drift parameters of the hydrogen maser
Table 1 - Frequency Stability of paper clock of traditional exponential filtering and Hydrogen masers
ADEV
Averaging time (h)
H226
H339
H341
Traditional
exponential filtering
1
9.68e-15
1.38e-14
1.46e-14
8.59e-15
2
7.04e-15
7.81e-15
7.96e-15
5.53e-15
4
6.49e-15
6.53e-15
7.08e-15
5.98e-15
8
7.09e-15
7.13e-15
7.39e-15
7.03e-15
16
6.82e-15
6.55e-15
6.92e-15
5.80e-15
32
4.98e-15
4.91e-15
5.26e-15
4.72e-15
64
4.58e-15
4.59e-15
6.35e-15
4.44e-15
128
3.45e-15
3.80e-15
9.96e-15
3.24e-15
256
2.97e-15
4.53e-15
1.87e-14
2.76e-15
38
IEEE Instrumentation & Measurement Magazine
August 2020
Instrumentation & Measurement Magazine 23-5
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