50 Khz Frequency Measurement Methods Table; 5 Mhz Frequency Measurement Methods Table - National Instruments NI cRIO-905x Series User Manual

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, the following table summarizes the
results.
Variable
fx
fk
Measurement time (ms)
N
Max. frequency error
(Hz)
Max. error %
From this, you can see that while the measurement time for one counter is shorter, the
accuracy is best in the sample clocked and two counter large range measurements. For another
example, the following table shows the results for 5 MHz.
Variable
fx
fk
Measurement time (ms
N
Max. frequency error
(Hz)
Max. error %
Again, the measurement time for the one counter measurement is lowest but the accuracy is
lower. Note that the accuracy and measurement time of the sample clocked and two counter
80 | ni.com | NI cRIO-905x User Manual
Table 19. 50 kHz Frequency Measurement Methods
Sample Clocked One Counter
50,000
80 M
1
—
.638
.00128
Table 20. 5 MHz Frequency Measurement Methods
Sample Clocked One Counter
5 M
80 M
1
—
62.51
.00125
High Frequency Large Range
50,000 50,000
80 M 1,000
.02
— —
31.27 1,000
.0625
High Frequency Large Range
5 M 5 M
80 M 1,000
.0002
— —
333 k 1,000
6.67 .02
Two Counters
50,000
80 M
1 1
—
.625
2 .00125
Two Counters
5 M
80 M
1 1
5,000
62.50
.00125