Chapter 7 Counters
X Series User Manual 7-16 ni.com
Figure 7-14. Large Range of Frequencies with Two Counters
NI-DAQmx then routes the Counter 0 Internal Output signal to the gate of
Counter 1. You can then route a signal of known frequency (fk) as a counter
timebase to the Counter 1 Source input. NI-DAQmx configures Counter 1
to perform a single pulse-width measurement. Suppose the result is that the
pulse width is J periods of the fk clock.
From Counter 0, the length of the pulse is N/fx. From Counter 1, the length
of the same pulse is J/fk. Therefore, the frequency of fx is given by
fx = fk *(N/J).
Sample Clocked Buffered Frequency Measurement
Sample clocked buffered point frequency measurements can either be a
single frequency measurement or an average between sample clocks. Use
CI.Freq.EnableAveraging to set the behavior. For buffered frequency, the
default is True. For hardware-timed single point (HWTSP), the default is
False.
A sample clocked buffered frequency measurement with
CI.Freq.EnableAveraging set to True uses the embedded counter and a
sample clock to perform a frequency measurement. For each sample clock
period, the embedded counter counts the signal to measure (fx) and the
Source Out
Counter 0
Source
Gate
Out
Counter 1
Signal to
Measure (fx)
Signal of Known
Frequency (fk)
CTR_0_SOURCE
(Signal to Measure)
CTR_0_OUT
(CTR_1_GATE)
CTR_1_SOURCE
Interval
to Measure
0 1 2 3 … N
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