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Pulse Frequency

The Pulse Frequency computed channel is designed to measure pulse frequencies, primarily in conjunction with Digital Input Channels. The system scans the logical input channel for falling edge and rising edge transitions. The pulse period is updated based on the time between rising-to-rising edges and falling-to-falling edges.

NOTE
The pulse counter frequency output is also update if the time period since the last set of edges exceeds the current output. This results in improved results as the pulse trains slows or stops.

ClosedScreenshot

ClosedGeneric parameters

  • Name: The computed channel name must be unique and contain valid characters (invalid characters are single and double quotes, '\', '@', '#', '&', '<', '>').
  • Collect: If checked, the channel data is written to the SIE data file during a test run.
  • Description: Optional detailed description of the computed channel.
  • Input channel: Select the desired input channel. In the edit dialog, the channel sample rate is displayed in Hz.
  • Measurand: The quantity being measured or the type of measurement associated with the computed channel.
  • Units: Physical units of measurement for the computed channel.
  • Range min and Range max: The expected extreme values of the computed channel output.
  • Output rate factor: Specify the down sample factor that determines the output channel sample rate. For example, for an input channel with a sample rate of 10000 Hz and an Output rate factor of 1000, the output channel sample rate is 10 Hz. The value must be an integer of 10 or greater.
  • Output scale factor: Specify the scale factor to convert the output data from Hz to the desired physical units. The Output scale factor cannot be zero.
  • Minimum output frequency: Specify the minimum frequency, f, of the output channel between 0.001 and 1.0 Hz. If a new pulse is not detected within the period of 1/f, the output value is set to f. The value remains at f until the detected pulse period is less 1/f. For example, if the minimum output frequency is 0.1 Hz and the input channel is a 50 Hz pulse train that suddenly stops, the pulse counter output remains at 50 Hz until a new pulse frequency is detected or until 10 seconds (1/f) have elapsed; at that point, the output value is set to 0.1 Hz. This minimum output frequency is also the initial output value until the first pulse is detected.

NOTE
The accuracy of the pulse frequency measurements depends on only the sample rate of the input channel. For example, using an input channel sampled at 2000 Hz provides 1% accuracy of a 20-Hz pulse signal and 0.1% of a 2-Hz pulse signal. As a general rule, the input sample rate should be 100 times the maximum expected pulse frequency to provide 1% or better accuracy of the entire pulse frequency range.

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Computed Channels