Programming instructions

Chapter 26 Measuring Frequency and Period
LabVIEW Data Acquisition Basics Manual 26-4
© National Instruments Corporation
Measuring the Frequency and Period
of High Frequency Signals
How you measure the frequencty and period of high frequency signals
depends on the counter chip on your DAQ device. If you are unsure of
which chip your DAQ device has, refer to your hardware documentation.
DAQ-STC
Figure 26-5 shows the Measure Frequency-Easy (DAQ-STC) VI located
in
labview\examples\daq\DAQ-STC.llb
. This example uses the
Easy VI, Measure Frequency which can be found in
Functions»
Data Acquisition»Counter
.
Figure 26-5.
Diagram of Measure Frequency-Easy (DAQ-STC) VI
This VI initiates the counter to count the number of rising edges of a
TTL signal at the SOURCE of counter during a known pulse at the GATE
of
counter
. The width of that known pulse is determined by
gate width
.
Frequency
is the output for this example, and
period
is calculated by
taking the inverse of the frequency. Remember, you must externally wire
your signal to be measured to the SOURCE of
counter
, and the OUT
of
counter-1
must be wired to the GATE of
counter
. For a complete
description of this example, refer to the information found in
Windows»Show VI Info…
.