NI cDAQ-9172 User Guide and Specifications 38 ni.com
Note If you are using an external signal as the Source, at least one Source pulse should
occur between each active edge of the Gate signal. This condition ensures that correct
values are returned by the counter. If this condition is not met, consider using duplicate
count prevention, described in the Duplicate Count Prevention section.
For information on connecting counter signals, refer to the Default
Counter/Timer Routing section.
Period Measurement
In period measurements, the counter measures a period on its Gate input
signal after the counter is armed. You can configure the counter to measure
the period between two rising edges or two falling edges of the Gate input
signal.
You can route an internal or external periodic clock signal (with a known
period) to the Source input of the counter. The counter counts the number
of rising (or falling) edges occurring on the Source input between the
twoactive edges of the Gate signal.
You can calculate the period of the Gate input by multiplying the period of
the Source signal by the number of edges returned by the counter.

Single Period Measurement

With single period measurement, the counter counts the number of rising
(or falling) edges on the Source input occurring between two active edges
of the Gate input. On the second active edge of the Gate input, the counter
stores the count in a hardware save register and ignores other edges on the
Gate and Source inputs. The software then reads the stored count.
Figure 21 shows an example of a single period measurement.
Figure 21. Single Period Measurement
SOURCE
GATE
Counter Value
HW Save Register
103
5
45
2