4-1.
INTERNAL TIME BASE AGING RATE (Cont’d)
4. Wait for a period of time (from 3 to 24 hours) and remeasure
the phase change time (repeat step
3). Record the period
of time between measurements (T2) in hours and the new phase change
time (T3) in seconds.
T2
=
hours (h)
T3
seconds
(5)
S. Calculate the aging rate from
the following equation:
Aging Rate
=
(1 cycle/f) (1/Ti
—
1/T3) (T/T2)
Where: 1 cycle
the phase change reference for the time measurement. (In this case, 360
degrees)
f= HP 8340B/41B Time Base output frequency (10 MHz)
T
=
specified time for aging rate (24 hours)
Ti
=
initial time measurement
(5)
for 360 degree (1 cycle change)
T2
=
time between measurements (h)
T3
=
final time measurement
(5)
for a 360 degree (1 cycle) change
For example, if:
Ti =351s
T2=3h
T3=349s
Then:
Aging Rate
=(i cycle/b
MHz)
(i/351s
—
i/349s) (24h/3h)
=i.3O6x10~11 per day
6. Verify that the aging rate is less than
9
per day.
NOTE
If the absolute frequencies of the frequency standard and the HP
8340B/41B Time Base oscillator are extremely close, the measurement
time in steps 3 and 4 (Ti and T3) can be reduced by measuring the time
required for a phase change of less than 360 degrees. change “1 cycle”
in the equation accordingly (i.e., 180 degrees
=
1/2 cycle, or 90 degrees
=
1/4 cycle).
7. If the aging rate is not within the required tolerance, be sure sufficient warmup time has been
allowed
and that the environmental conditions have not changed throughout the test, then check
the Time Base heater circuit and,
if necessary, replace the Time Base. Refer to service and repair
information for the ASi 10 MHz Reference Oscillator in the Reference Loop
—
M/N Loop portion
in Section VIII of the Service Manual.
HP 8340B/41B
Performance Tests
4-11/4-12