Making Frequency Measurements

You can measure the signal frequency on specified channels by using the following:
  • niDigital Frequency Counter Configure Measurement Time VI
  • niDigital Frequency Counter Measure Frequency VI
  • DigitalFrequencyCounter.Configure .NET property
  • DigitalFrequencyCounter.MeasureFrequency .NET method
  • niDigital_FrequencyCounter_ConfigureMeasurementTime C function
  • niDigital_FrequencyCounter_MeasureFrequency C function

Use the VOL comparators to count the number of rising edges through the VOL threshold over the measurement time. To ensure accurate measurements, ensure that the input signal produces at least five rising edges within the measurement time, is free-running, and has monotonic rising and falling-edges through the VOL threshold.

The PXIe-6571 has a discrete frequency counter per eight digital input channels to measure the frequency on those channels. For the PXIe-6571 (32-channel), you can optimize frequency measurements for test time if the channels you want to measure are from different frequency counters.

Table 8. Frequency Counters and Associated Channels
Frequency Counter Channels
1 <0..7>
2 <8..15>
3 <16..23>
4 <24..31>

Refer to PXIe-6571 Specifications for the supported frequency measurement ranges.