User Guide

NI cDAQ-9172 User Guide and Specifications 46 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

two active 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