HP 8648 A/B/C/D - Changpuak.ch

Internal Timebase:
Aging Rate
Performance Tkst
(Option lE5 Only)
Internal Timebase: Aging Rate Performance Test (Option lE5 Only)
Description This procedure checks the accuracy of the internal timebase. The
time required for a specific phase change is measured both before
and after a specified waiting period. The aging rate is inversely
proportional to the absolute value of the difference in the measured
times.
The overall accuracy of the internal timebase is a function of:
TBC &AR fTE fLE where:
TBC = timebase calibration
TE = temperature effects
AR = aging rate
LE = line effects
After the timebase is adjusted, the timebase frequency should stay
within the aging rate if the following things happen:
The timebase oven does not cool down.
The instrument keeps the same orientation with respect to the
earth’s magnetic field.
The instrument stays at the same altitude.
The instrument does not receive any mechanical shock.
If the timebase oven cools (the instrument power switch is set to
off), you may have to readjust the timebase frequency after a new
warm-up cycle. Typically, however, the timebase frequency returns to
within f 1 Hz of the original frequency.
Note The internal timebase can be tested after reconnecting AC power for
10 minutes, but for best accuracy, test again after the instrument has
been on for 24 hours.
Frequency changes due either to a change in orientation with respect
to the earth’s magnetic field, or to a change in altitude, usually go
away when the instrument is returned to its original position. A
frequency change due to mechanical shock usually appears as a fixed
frequency error.
Performance Tests 8-35