Internal Time Base Aging Rate - HP 8340B Manual

4-1.
INTERNAL TIME BASE AGING RATE
NOTE
The
overall
accuracy
of the HP 8340B/41B 10
MHz internal time base
is
a
function of time
base
calibration ± aging rate ±
temperature effects
±
line
effects.
For greatest frequency accuracy, the time base should be allowed to
warm up
until the output frequency has stabilized (usually
7
to 30 days)
before calibrating (adjusting the time base frequency to
a known stan¬
dard). After calibration, the change in time
base frequency should
remain within the aging rate if: the time base
oven
is
not allowed to cool
down, the instrument orientation
with
respect
to the earth's magnetic
field
is
maintained, and the instrument does not sustain any mechanical
shock. Frequency changes due to orientation with respect to the earth's
magnetic
field
and altitude changes
will usually be nullified when
the
instrument
is
returned
to its original position. Frequency changes due to
mechanical shock
will
usually
appear as a
fixed frequency error.
If
the instrument is
disconnected from ac power allowing the time base
oven to cool down,
it
may be necessary to readjust the time base
fre¬
quency after
a
new warmup cycle; however,
in most cases, the time base
frequency
will return to within
±
1 Hz of the
original frequency.
Specification
Table 4-3. Internal Time Base Aging Rate Specifications
Aging Rate;
1x10-9 per
day,
2.5x10-7 per year after 72-hour warm up
if
the instrument has been disconnected
from ac
power
for less than 24 hours. Aging rate
is achieved after
7
to
30
days warm-up
if
the
instrument has been disconnected from ac power for greater than 24 hours.
Accuracy:
Overall accuracy of
internal time base
is
a
function of time base calibration
± aging rate ±
temperature effects
± line effects.
Description
A
reference
signal from the HP 8340B/41B
under test
is
connected to the oscilloscope's vertical
input.
A frequency standard (with long term stability
greater
than 1x10-10
is
connected
to the oscilloscope
trigger
input.
The
time required for
a
specific phase change
is
measured immediately and after
a
period of time. The aging rate
is inversely proportional to the absolute value of the difference in the
measured times.
Equipment
Frequency Standard
Oscilloscope1
.....
HP 5061
A
HP1741A
1 A
50 Ohm
Feedthrough Termination (such as
the HP 10100C)
is required when using an oscilloscope without
a
50 Ohm input It is
not required
with
the HP 1741A
HP 8340B/41B
Performance Tests 4-9