HP 8340B Manual page 14

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.
S. Calculate the aging rate from
Aging Rate
=
Where: 1 cycle
For example, if:
Then:
Aging Rate
6. Verify that the aging rate is less than
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
1/4 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
in Section VIII of the Service Manual.
HP 8340B/41B
the following equation:
1/T3) (T/T2)
(1 cycle/f) (1/Ti
—
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
=
T2 time between measurements (h)
=
final time measurement (5) for a 360 degree (1 cycle) change
T3
=
Ti =351s
T2=3h
T3=349s
MHz) (i/351s
=(i cycle/b
=i.3O6x10~ 11 per day
per day.
9
T2
T3
for 360 degree (1 cycle change)
(5)
i/349s) (24h/3h)
—
NOTE
1/2 cycle, or 90 degrees
=
hours (h)
=
seconds (5)
M/N Loop portion
—
Performance Tests 4-11/4-12