Chapter 7
Counters
©
National Instruments Corporation
7-11
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.
P
u
l
s
e
F1
P
u
l
s
e
F1
G
a
te
S
o
u
rce
1 2 …
N
P
u
l
s
e-Width
Me
asu
rement
T =
N
F1
Freq
u
ency of F1 =
T
Width of
P
u
l
s
e
N
Width of P
u
l
s
e (T)
