8-3
8.3 Calibration
8.3 Calibration
The frequency of the internal reference oscillator that creates time base is a critical element influencing measurement
accuracy of a frequency counter. This means that in order to maintain a high degree of measurement accuracy you must
periodically calibrate the frequency of the reference oscillator using a standard frequency with guaranteed accuracy.
Even if you have a reference oscillator with good stability, the measurement result will not exceed the calibrated accuracy
if the calibrated accuracy was a low value. For example, the accuracy variation is 5 × 10
–10
or less per day when using a
signal with an accuracy of 5 × 10
–8
to calibrate a reference oscillator that has a high stability of aging rate 5 × 10
–10
.
However, the measurement accuracy will never be better than 5 × 10
–8
. In other words, this calibration method is not
getting the most out of the performance of the high stability of 5 × 10
–10
/day.
Conversely, if the stability lowers, the high degree of accuracy is meaningless. Consequently, matching the stability and
accuracy of the reference oscillator is the most effective calibration method.
When continually use the frequency counter more than one month or storage it more than one month, the reference osillator
should be calibrated as following procedure.
(1) Turn the counter on for at least 24 hours in a 25 ˚C ±5 ˚C room until it warms up adequately.
(2) Receive a frequency standard, standard radio wave receiver, or color TV subcarrier (NHK and TV Asahi use signals
locked to a rubidium atom standard), and then connect the signal generator for generating a signal locked to this and
this unit as shown in Figure 8-1.
(3) Set the signal generator to 1 GHz.
(4) Set the unit as follows after settings presets.
Input channel : Input2
Measurement resolution : 10 Hz or less
(5) While turning the crystal oscillator’s correcting potentiometer from the internal standard adjustment aperture on the
right side board, read the equipment’s frequency value and adjust to a resolution up to 10 Hz. Adjust options 01 and
02 of the crystal oscillator to a resolution up to 1 Hz and option 03 to a resolution up to 0.1 Hz.
Input2
RF
Ref
Input
Output
1 GHz
Output
10 MHz
Host standard Signal generator MF2412B/MF2413B/MF2414B
Fig. 8-1 Example of Connections for calibration
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