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
Description
A reference signal from the HP 8340B/41 B under test is connected to the
oscilloscope’s vertical input.
A frequency standard (with long term stability greater than 1x10’O 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
HP 5061A
Oscilloscope1
HP 1741A
Aging Rate:
lxlO—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.
1. A 50 Ohm Feedthrough Termination Isuch as the HP 101 OOC) 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