Valid Sampling Rates for NI DSA Devices

Updated Mar 19, 2019

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 Dynamic Signal Acquisition (DSA) devices have discrete sampling rates. Requesting a different rate will result in the module defaulting to the discrete rate closest to the requested sampling rate.

It is possible to read the actually used sample rate using the DAQmx Timing Property Node:

Additional Information

NI Dynamic Signal Acquisition (DSA) devices have discrete sample rates, because the class of DSA modules utilize a type of Analog to Digital Converter (ADC) called a Delta-Sigma ADC. These require oversampling, which means they require their own Sample Clock Timebase. These timebases can only be divided down by discrete numbers.


For C Series Modules, all sampling rates supported by your device are stated in its user manual, in the section Data Rates. There you will either find a formula that can be used to determine the available rates, or a table. The following table shows the sampling rates supported by the modules NI-9234 and NI-9237 as example:
NI-9234NI-9237
in kHzin kHz
1.6521.613
1.7071.667
1.7661.724
1.8291.786
1.8961.852
1.9691.923
2.0482.000
2.1332.083
2.2262.174
2.3272.273
2.4382.381
2.5602.500
2.6952.632
2.8442.778
3.0122.941
3.2003.125
3.4133.333
3.6573.571
3.9383.846
4.2674.167
4.6554.545
5.1205.000
5.6895.556
6.4006.250
7.3147.143
8.5338.333
10.24010.000
12.80012.500
17.06716.667
25.60025.000
51.20050.000

For i.a. NI-446x, NI-447x, and NI-449x devices the respective formulae are stated in NI Dynamic Signal Acquisition User Manual  starting on page 2-24.


If you use an NI-9237 in the same task as an NI-9234, both 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:

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