Configuring a Counter to Measure Period (Scan Interface)

CompactRIO Scan Interface

Configuring a Counter to Measure Period (Scan Interface)

You can configure a digital input channel as a counter to measure the period of a signal connected to the channel. The counter returns data in µs. You can configure the following options for a period measurement counter. Use the Measurement Edge control to specify Rising Edge or Falling Edge.

Configuring the Input Filter

You can add an input filter to all input channels of the module. A filter removes noise, glitches, and spikes on inputs by rejecting signals with periods shorter than the specified length. You can select one of the following options.

  • Disabled—The hardware synchronizes the digital inputs using a 4 MHz timebase. Pulses longer than 250 ns are always detected. Pulses shorter than 250 ns may be rejected.
  • 1 µs—Pulses shorter than 1 µs are rejected. Pulses between 1 µs and 2 µs are sometimes detected. Pulses longer than 2 µs are always detected.
  • 16 µs—Pulses shorter than 16 µs are rejected. Pulses between 16 µs and 32 µs are sometimes detected. Pulses longer than 32 µs are always detected.
  • 256 µs—Pulses shorter than 256 µs are rejected. Pulses between 256 µs and 512 µs are sometimes detected. Pulses longer than 512 µs are always detected.
  • 4096 µs—Pulses shorter than 4096 µs are rejected. Pulses between 4096 µs and 8192 µs are sometimes detected. Pulses longer than 8192 µs are always detected.

Selecting the Measurement Edge

  • Rising Edge—The counter measures the time from one rising edge to the next rising edge.
  • Falling Edge—The counter measures the time from one falling edge to the next falling edge.