Measuring Ocxo Stable Frequency Deviation - National Instruments NI 660 Series User Manual

Measuring OCXO Stable Frequency Deviation

When you power the NI 6608 device, the OCXO requires adequate
warm-up time to reach stable frequency. Five minutes is adequate warm-up
time for a power-off duration of less than one hour, with maximum
deviation within 20 ppb, or parts per billion, while four hours of operation
is adequate for a power-off duration of up to 90 days.
For best performance, minimize power-off periods for the OCXO.
Note
The OCXO is calibrated to within 0.1 Hz of 10.000000 MHz prior to
shipment. Table 2-2 shows additional change in stable frequency that
occurs over time. A change in stable frequency of approximately 45 ppb
occurs after the first year of normal use.
For example, if the OCXO has a perfect stable frequency of 10 MHz after
warm-up, after the first 10 days of operation, the stable frequency drifts
11.25 ppb. During the next 50 days of operation, this frequency will drift
an additional 11.25 ppb, thus making the total drift caused by aging to be
22.5 ppb. After 365 days, drift will be 45 ppb. If you calibrate the OCXO
after 365 days of operation to restore the stable frequency to a perfect
10 MHz, the drift during the first 10 days following calibration
(days 366-375) will now be 5.63 ppb—the stable frequency in this case will
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Table 2-2. Change in Stable Frequency over Time
Days of Operation
0-10
11-60
61-200
201-365
366-375
376-425
426-565
566-730
731-740
741-790
2-11
Chapter 2 Device Overview
Additional Change in
Stable Frequency (ppb)
11.25
11.25
11.25
11.25
5.63
5.63
5.63
5.63
2.82
2.82
NI 660x User Manual