Figure 63. Sample Clocked Buffered Frequency Measurement (Averaging)
Gate
(fx)
Source
(fk)
Sample
Clock
Counter Armed
S1
S2
S3
T1 T2
1 6
T1 T2
1 7
2 10
T1 T2
1 7
2 10
1 6
Buffer
1
2
1
6
10
6
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 as shown in the following
figure.
Figure 64. Sample Clocked Buffered Frequency Measurement (Non-Averaging)
Gate
Source
Sample
Clock
Counter Armed
Latched
Values
6
6
4
6
4
6
4
6
6
With sample clocked frequency measurements, ensure that the frequency to measure is twice
as fast as the sample clock to prevent a measurement overflow.
Choosing a Method for Measuring Frequency
The best method to measure frequency depends on several factors including the expected
frequency of the signal to measure, the desired accuracy, how many counters are available, and
how long the measurement can take. For all frequency measurement methods, assume the
following:
fx
is the frequency to be measured if no error
fk
is the known source or gate frequency
Measurement Time
(
T
) is the time it takes to measure a single sample
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cRIO-904x User Manual
