National Instruments Network Device DAQ S - Manual (Page 83)

Chapter 7 Counters
© National Instruments Corporation 7-11 NI 6124/6154 User Manual
Figure 7-12 illustrates this method. Another option would be to
measure the width of a known period instead of a known pulse.
Figure 7-12. Method 2
• Method 3: Measure Large Range of Frequencies Using
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. In this method, you generate a long
pulse using the signal to measure. You then measure the long pulse
with a known timebase. The S Series device can measure this long
pulse more accurately than the faster input signal.
Pulse
F1
Pulse
F1
Gate
Source
1 2 … N
Pulse-Width
Measurement
T =
N
F1
Frequency of F1 =
T
Width of
Pulse
N
Width of Pulse (T)