You can configure channels of some C Series digital input modules as counters. Counter channels measure digital signals. Counters are used commonly to count edges. Counters are also used for time measurements, such as measuring the frequency or period of a signal.

Input Filter

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

  • 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.

    • Counter Measurement Modes

    You can select one of four counter measurement modes for each counter channel:
    • Count Edges
    • Period Measurement
    • Pulse-Width Measurement
    • Frequency Measurement