Sampling Rate of NI 9235/9237 Is Not Adjusted to Data Rate on FlexLogger

Updated Sep 8, 2020

Reported In

Hardware

  • NI-9235
  • NI-9237

Software

  • FlexLogger

Issue Details

I am using NI 9235 and 9237 on FlexLogger.  While the data rate is 100 Hz, the actual sampling rate of the two modules were 794 S/s (NI 9235) and 1.613 kS/s (NI 9237). Other modules are working as expected. Why?
 

Solution

There is the minimum data rate for some modules. Since FlexLogger does not support using an external timebase for those modules, the minimum data rates of the modules are 794 S/s (NI 9235) and 1.613 kS/s (NI 9237). FlexLogger displays an "Actual Sample Rate" when it tries to configure a lower sample rate than the minimum (or a sample rate that is not divided from the timebase).

To log fewer samples by using a slower sample rate, you can enable the Preview Feature "Enable downsampling from coerced hardware sample rate to slower sample rate". FlexLogger would downsample the data to the requested rate. It is important to note that the module would still be using its minimum sample rate, but FlexLogger would resample the data to the requested rate.