Two-Edge Separation Measurement

You can take two-edge separation measurements with the NI-9361 on CompactRIO systems only.

The counter measures the time between two events. The beginning event is an active edge on a first signal. The ending event is an active edge on a second signal. The NI-9361 returns the current time between the two events in the number of ticks of the 100 MHz counter timebase when the counter is read. The following figure shows an example of two-edge separation measurement.

Figure 18. Two-Edge Separation

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Channel Settings

You can configure the following counter properties:
  • Input terminal of the first signal.
  • Input terminal of the second signal.
  • The active edge of the first signal, rising or falling, the NI-9361 begins the measurement.
  • The active edge of the second signal, rising or falling, the NI-9361 ends the measurement.
  • Maximum measurable separation—You can set the maximum measurable separation of the signals. If separation time between the first and second signals is longer 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 returning previous measurements. To disable this feature, set the maximum measurable separation 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 two-edge separation measurement through the counter arm control. After the counter is armed, it waits for the active edge on the first signal, and then it begins measuring the separation. The measurement data is only ready and valid once the counter has finished measuring the separation between the first and second edges. 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.