Frequency Measurements In NI MAX With "1 Sample (On Demand)"

Updated Apr 25, 2018

Reported In

Hardware

  • NI-9423

Driver

  • NI-DAQmx

Issue Details

I am doing a frequency measurement using a counter input. I am setting my task up in NI MAX, and choose my acquisition mode as 1 Sample (On Demand), but I see the frequency of my digital signal fluctuate. Why is this? 

Solution

The 1 Sample (On Demand) acquisition mode retrieves one sample (which is the number of ticks the counter has incremented) and compares it to the timebase to calculate frequency. Because On Demand is software timed, this timebase is not stable, and will not provide accurate frequency measurements. Change to Continuous or Finite acquisition for more accurate results (1 SampleHW Timed is not supported on cDAQ chassis). 

WAS THIS ARTICLE HELPFUL?

Not Helpful