© National Instruments
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5-11
NI cDAQ-9132/9133/9134/9135/9136/9137 User Manual
Frequency Measurement
You can use the counters to measure frequency in several different ways. Refer to the following
sections for information about cDAQ controller frequency measurement options:
•
Low Frequency with One Counter
•
High Frequency with Two Counters
•
Large Range of Frequencies with Two Counters
•
Sample Clocked Buffered Frequency Measurement
Low Frequency with One Counter
For low frequency measurements with one counter, you measure one period of your signal using
a known timebase.
You can route the signal to measure (
fx
) to the Gate of a counter. You can route a known timebase
(
fk
) to the Source of the counter. The known timebase can be an onboard timebase, such as
80 MHz Timebase, 20 MHz Timebase, or 100 kHz Timebase, or any other signal with a known
rate.
You can configure the counter to measure one period of the gate signal. The frequency of
fx
is
the inverse of the period. Figure 5-12 illustrates this method.
Figure 5-12.
Low Frequency with One Counter
fx
fk
G
a
te
S
o
u
rce
1
2
3
…
N
S
ingle Period
Me
asu
rement
…
Period of
fx
=
N
Fre
qu
ency of
fx
=
N
Interv
a
l Me
asu
red
fk
fk
fk
fx
