Pulse/Duty Cycle Measurement

You can take pulse or duty cycle measurements with the NI-9361 on CompactRIO systems only.

The counter measures the high and low durations of a pulse on a signal. Using the measured values, you can calculate the duty cycle of the signal. The NI-9361 returns the current measurement values when the counter is read. The measurement values consist of the high and low times of the pulse in the number of ticks of the 100 MHz counter timebase.

You can calculate the signal period using the following equation:
S i g n a l ⁢   P e r i o d = T p u l s e h i g h + T p u l s e l o w
where
  • Tpulsehigh is the pulse high time
  • Tpulselow is the pulse low time

You can calculate the duty cycle using the following equation:

D u t y ⁢     C y c l e = T p u l s e h i g h S i g n a l ⁢   P e r i o d
The following figure shows an example of pulse measurement.

Figure 11. Pulse 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.
  • 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 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 signal high and low times. The measurement data is only ready and valid once the counter has finished measuring the first signal period. The counter returns a value of zero for both the high and low times prior to the first measurement becoming ready. Refer to your software documentation for more information on arming the counter.