User Guide

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.

Frequency Measurement

You can use the counters to measure frequency in several different ways.

You can choose one of the following methods depending on your

application: Method 1, Method 1b, Method 2, and Method 3.

Method 1—Measure Low Frequency With One Counter

This method is good for low frequency signals. Use this method to measure

one period of your signal using a known timebase. Figure 24 illustrates this

method.

Figure 24. Frequency Measurement—Method 1

You can route the signal to measure (F1) to the Gate of a counter. You can

route a known timebase (Ft) to the Source of the counter. The known

timebase can be 80MHzTimebase. For signals that might be slower than

0.02 Hz, use a slower known timebase.

You can configure the counter to measure one period of the gate signal. The

frequency of F1 is the inverse of the period.

Gate

Source

1 2 3 … N

Single Period

Measurement

…

Period of F1 =

Frequency of F1 =

Interval Measured