HP 8340B Manual page 17

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 (s)
5.
Calculate the aging rate from the following equation:
Aging Rate
=
(1 cycle/f) (1/T1
-
1/T3) (T/T2)
Where:
1
cycle
=
the phase change reference for the time measurement.
(In this
case, 360
degrees)
f
=
HP 8340B/41
B
Time Base output frequency (10 MHz)
T
=
specified time for
aging
rate (24 hours)
T1
=
initial
time measurement (s) for 360 degree (1 cycle change)
T2
=
time
between measurements (h)
T3
=
final
time measurement (s) for
a
360 degree (1
cycle)
change
For example,
if:
T1=351s
T2=3h
T3
==
349s
Then:
Aging Rate =(1
cycle/10 MHz) (1/35-ls
-
1/349s) (24h/3h)
=1.306x10-11
per day
6.
Verify that the aging rate is less than -s
per day.
NOTE
If the
absolute frequencies of the frequency standard and the
HP
8340B/41 B
Time Base oscillator
are extremely
close, the
measurement
time in
steps
3
and
4
(T1 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
A5110 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