Chapter 2
Device Overview
©
National Instruments Corporation
2-11
Measuring OCXO Stable Frequency Deviation
When yo
u
power the NI 6608 device, the OCXO req
u
ires adeq
u
ate
warm-
u
p time to reach stable freq
u
ency. Five min
u
tes is adeq
u
ate warm-
u
p
time for a power-off d
u
ration of less than one ho
u
r, with maxim
u
m
deviation within 20 ppb, or parts per billion, while fo
u
r ho
u
rs of operation
is adeq
u
ate for a power-off d
u
ration of
u
p to 90 days.
Note
For best performance, minimize power-off periods for the OCXO.
The OCXO is calibrated to within 0.1 Hz of 10.000000 MHz prior to
shipment. Table 2-2 shows additional change in stable freq
u
ency that
occ
u
rs over time. A change in stable freq
u
ency of approximately 45 ppb
occ
u
rs after the first year of normal
u
se.
For example, if the OCXO has a perfect stable freq
u
ency of 10 MHz after
warm-
u
p, after the first 10 days of operation, the stable freq
u
ency drifts
11.25 ppb. D
u
ring the next 50 days of operation, this freq
u
ency will drift
an additional 11.25 ppb, th
u
s making the total drift ca
u
sed by aging to be
22.5 ppb. After 365 days, drift will be 45 ppb. If yo
u
calibrate the OCXO
after 365 days of operation to restore the stable freq
u
ency to a perfect
10 MHz, the drift d
u
ring the first 10 days following calibration
(days 366–375) will now be 5.63 ppb—the stable freq
u
ency in this case
Table 2-2.
Change in Stable Frequency over Time
Days of Operation
Additional Change in
Stable Frequency (ppb)
0–10
11.25
11–60
11.25
61–200
11.25
201–365
11.25
366–375
5.63
376–425
5.63
426–565
5.63
566–730
5.63
731–740
2.82
741–790
2.82
