NuDAQ PCI-8554, Руководство пользователя

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Signal Connection and Applications
4.6 Frequency Measurement
Example: To measure frequency around 1~100 K Hz
step 1: This application need two counters. One counter is used to
generate a pulse whose time interval is very precise. The
pulse is used to enable the other counter (counting counter)
by gate control. The gate control is coming from
/COUT3 .
In this example, cascaded counter is used, the pulse
generator is counter #3 ( clock is from
COUT2 ) and the
counter #1 is used to measure frequency.
step 2 : The maximum value of counting counter is no more than
65535, For measuring 100 K Hz frequency, the time interval
should be within 1/100 K Hz x 65535 = 0.655 sec. If the time
interval is wider, then the measurement resolution is better,
however, the counting value will be overflow if time interval
is too long. That means the low pulse width of counter #3
output should shorter than 0.655 sec. User can try to
generate the pulse by counter #3 by yourself.
step 3: Connect the signal to be measured to th e ECLK1 and
adjust JP1 to select debounce function.
step 4: Connect GATE1 to /COUT3 .
step 5: The following block diagram illustrates the application.
Write and verify the control program. The frequency of the
signal is:
frequency = counting value of counter #1 / precise time interval
Please refer the ‘DEMO4.C’ source code.