HP 8642A Operation And Calibration Manual page 303

Model 8642A/B Performance Tests
PERFORMANCE TESTS
for example:
if:
T1
= 351s
T2
=
349s
T3
=
3h
then:
Aging Rate
=
(
1 cycle
10 MHz
) ( _ 1
351s
1.306
X
10-
11
7. Record the aging rate.
-34-=-~-S-)
(
234~1
)
Aging Rate _ _ _ _ _ 5 x la-la/day
NOTE
]j the absolute frequencies of the frequency standard
and the HP 8642's reference oscillator are extremely
close, the measurement time in steps
4
and
5
(T I and
T 2) can be reduced by measuring the time required
for a phase change of something less than 360
degrees. Change I cycle in the formula (e.g., 180
degrees:: 1/2 cycle, 90 degrees:: 1/4 cycle).
8.
If the rate aging is not within the required tolerance, check the power
supplies before replacing A8A3. Be sure sufficient warm-up time has
been allowed (may require up to 10 days).
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