Pulse Width Measurement

You can take pulse width measurements with the NI-9361.

The counter measures and returns the duration of a pulse on a signal. The NI-9361 returns the current pulse width measurement value when the counter is read. The measurement values consist of the pulse width duration of the signal-to-measure in the number of ticks of the 100 MHz counter timebase. The following figure shows an example of pulse width measurement.

Figure 17. Pulse Width Measurement

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Channel Settings

You can configure the following counter properties:
  • Input terminal of the signal-to-measure.
  • The active edge, rising or falling, the NI-9361 begins the measurement. To measure a high pulse, set the active edge to rising. To measure a low pulse, set the active edge to falling.
  • Maximum measurable period—You can set the maximum measurable period of the signal. If the input signal period is slower than this value, the counter returns a measurement value of zero. Use this property to get updated measurement data when the signal slows down or is stopped instead of previous measurements. To disable this feature, set the maximum measurable period to zero. When this feature is disabled, the counter keeps measuring until a valid measurement is detected, the counter overflows, or the user stops the counter.

Trigger Settings

Counter Arm—You can control when the counter starts the pulse width measurement through the counter arm control. After the counter is armed, it waits for the active edge on the signal-to-measure, and then it begins measuring the pulse width. The measurement data is only ready and valid once the counter has finished measuring the first pulse width. The counter returns a value of zero prior to the first measurement becoming ready. Refer to your software documentation for more information on arming the counter.