Figure 7.
Time interval measurement.
calibrated periodically, since the drift rate will cause a cumulative
deviation in frequency which can result in a measurement error.
The
accuracy of precision quartz oscillators is usually expressed as long term
stability and short term stability.
Long term stability refers to slow
changes in average frequency with time due to secular changes in the
resonator or other elements of the oscillator. Short term stability refers
to changes in average frequency over a time sufficiently short so that the
change in frequency due to long term effect is negligible.
Four methods
have been developed which extend the digital frequency measuring
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