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Chapter 5
Counters
Figure 5-13 illustrates this method. Another option is to measure the width of a known period
instead of a known pulse.
Figure 5-13.
High Frequency with Two Counters
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 cDAQ chassis 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.
P
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l
s
e
fx
P
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fx
G
a
te
S
o
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1
2
…
N
P
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e-Width
Me
asu
rement
T
=
N
fx
Fre
qu
ency of
fx
=
T
Width of
P
u
l
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e
N
Width of P
u
l
s
e (
T
)
