Figure 6.
Ratio measurement.
illustrates that separate signals may be used as the start and stop signals,
and when the COM-SEP switch is placed in the COM position, measurements may
be made from one point on a waveform to another point on the same waveform.
Triggering polarity, slope, and amplitude are selected for each channel
separately. The time interval is displayed in microseconds, milliseconds,
or seconds.
f. Multiple-Period Averaging. The effects of the previously mentioned
1 count ambiguity and the trigger error can each be reduced in decade
steps by using multiple period averaging (figure 8). In many high frequency
counters, the function selector is ganged to the decade divider assemblies
so that the input signal can be scaled in decade steps by factors up to
100,000 to reduce trigger error. The 1 count error is also reduced by a
factor of 10 for each decade of scaling selected for the input signal.
g. High
Frequency
Measuring
Methods.
Precise
high
frequency
measurements are possible because of several innovations in quartz
oscillator crystal design.
These innovations have resulted in superior
electronic counter time bases. Ambient temperature affects the frequency by
less than 2 parts in 1010 per degree C throughout the range from -20 to
+50 degrees C.
The accuracy of the counter is limited by the time base
oscillator stability because this oscillator circuit furnishes the
definitive time information for a measurement. The time base must be
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