Valid Sampling Rates for NI DSA Devices

Updated Oct 2, 2018

Reported In

Hardware

  • NI-9237
  • NI-9234
  • NI-9227
  • NI-9230
  • NI-9231
  • NI-9232
  • NI-9250
  • NI-9218
  • NI-9219
  • PCI-4461
  • PCI-4462
  • PXI-4461
  • PXI-4462
  • PXIe-4463
  • PXIe-4464
  • PXIe-4480
  • PXIe-4492
  • PXIe-4497
  • PXIe-4499
  • USB-4431
  • USB-4432
  • NI-9229

Issue Details

  • When I set a constant sampling rate on my NI Dynamic Signal Acquisition (DSA) device, that rate appears to change, or my data is sampled at a different rate than what I requested.
  • My data seem unexpected based on the constant sampling rate I have set. Am I using an invalid sampling rate on my NI DSA device?

Solution

NI DSA devices have discrete sampling rates. Requesting a different rate will result in the module defaulting to the closest discrete rate to the requested sampling rate.

You can determine what rates your device supports sampling at by going to the user manual for your device, and looking under Data Rates. The data rates can be determined using the formula given in the manual. 

An example of these rates (in kHz) are given below for the NI 9234 and the NI 9237.
 

Additional Information

These devices have discrete sample rates because they fall into a class of devices called DSA modules. DSA modules all utilize a type of ADC called a Delta-Sigma ADC. DSA modules require oversampling, which means they require their own Sample Clock Timebase. These timebases can only be divided down by discrete numbers.

Note: If you have a 9237 in a task with a 9234, it will run at the 9234's rates by default. This is because DAQmx synchronizes multiple modules by automatically routing the faster master timebase to the other modules. However, you can force the task to use any of the available timebases by manually setting the Sample Clock Timebase Source property using the DAQmx Timing property node.
If the specified sample rate does not match one of the allowable values, then it gets coerced up to the next valid sample rate. In order to determine the actual sample rate of the device, use the property node below.

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