5-16 | ni.com
Chapter 5 Counters
Which Method Is Best?
This depends on the frequency to be measured, the rate at which you want to monitor the
frequency and the accuracy you desire. Take for example, measuring a 50 kHz signal. Assuming
that the measurement times for the sample clocked (with averaging) and two counter frequency
measurements are configured the same, Table 5-3 summarizes the results.
Table 5-3. 50 kHz Frequency Measurement Methods
Variable
Sample
Clocked
One Counter
Two Counter
High
Frequency
Large Range
fx 50,000 50,000 50,000 50,000
fk 80 M 80 M 1,000 80 M
Measurement
time (mS)
1 .02 1 1
N — — — 50
Max. frequency
error (Hz)
.638 31.27 1,000 .625
Max. error % .00128 .0625 2 .00125
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