Chapter 7 Counters
© National Instruments 7-17 X Series User Manual
primary counter counts the internal time-base of a known frequency (fk).
Suppose T1 is the number of ticks of the unknown signal counted between
sample clocks and T2 is the number of ticks counted of the known
time-base. The frequency measured will be fx = fk * (T1/T2).
Figure 7-15. Sample Clocked Buffered Frequency Measurement (Averaging)
When CI.Freq.EnableAveraging is set to false, the frequency measurement
returns the frequency of the pulse just before the sample clock. This single
measurement is a single frequency measurement and is not an average
between clocks.
Figure 7-16. Sample Clocked Buffered Frequency Measurement (Non-Averaging)
With sample clocked frequency measurements, ensure that the frequency to
measure is twice as fast as the sample clock to prevent a measurement
overflow.
Gate
(fx)
Source
(fk)
Sample
Clock
Counter Armed
S1 S2 S3
T1 T2
1
6
T1 T2
17
210
T1T2
1
7
2
10
1
6
Buffer
121
6106
Gate
Source
Sample
Clock
Counter Armed
Latched
Values
6
646
4
6
4
6
6
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