Large Range Of Frequencies With Two Counters - National Instruments X Series User Manual

Figure 7-13 illustrates this method. Another option is to measure the width of a known period
instead of a known pulse.
Pulse Gate
fx Source
Pulse-Width
Measurement

Large Range of Frequencies with Two Counters

By using two counters, you can accurately measure a signal that might be high or low frequency.
This technique is called reciprocal frequency measurement. When measuring a large range of
frequencies with two counters, you generate a long pulse using the signal to measure. You then
measure the long pulse with a known timebase. The X Series device can measure this long pulse
more accurately than the faster input signal.
Note Counter 0 is always paired with Counter 1. Counter 2 is always paired with
Counter 3.
Figure 7-13. High Frequency with Two Counters
Pulse
fx
Width of Pulse ( T )
1 2 ...
Width of
T =
Pulse
Frequency of fx =
X Series User Manual
N
N
fx
N
T
© National Instruments | 7-13