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Valid Sampling Rates for the NI 9233, NI 9234, and NI 9237

Hardware: PXI/CompactPCI>>Controllers

Problem:
I would like to acquire data for an audio application. When I set the sample rate on my NI 923X to be 44.1kHz, the actual sample rate gets coerced to 50kHz. What are the valid sample rates for the NI 923X?

Solution:
The valid sampling rates can be found in the user guide and specifications manual for each module in the related links section, and are reproduced here.

Figure 1 displays allowable sampling rates for the NI 9233, NI 9234, and NI 9237. The NI 9234 sample rates are displayed using the NI 9234 internal time base. 

 

Figure 1(values in kS/s)

Valid sample rates for the NI 9233 obey the following formula:
Fs = 100kS/s / N, where N is an integer 2, 3.
Fs = 50kS/s / N, where N is an integer 2..25.

Valid sample rates for the NI 9234 obey the following formula:
Fs = (Fm / 256) / N, where N is an integer 1..31.
Where Fm is the internal time base. By default Fm is 13.1072 MHz.

Valid sample rates for the NI 9237 obey the following formula:
Fs = 50kS/s / N, where N is an integer 1..31.

*Note: If you have a 9233 or 9237 in a task with a 9234 it will run at the 9234 rates by default.  This is because a Compact DAQ chassis synchronizes multiple modules by routing the sample clock of the slowest module to the other modules within that same task.

If the specified sample rate does not match one of the allowable values, then it gets coerced up to the next valid sample rate. For information on determining the actual sample rate of your device, view the KnowledgeBase entries listed in the related links section.

To change the sampling rate of a previously obtained signal in LabVIEW, the Resample Waveform (Continuous).vi can be used as shown in Figure 2.

Figure 2

This VI requires the input signal in waveform format, desired sampling period (1/desired sampling frequency) and an interpolation type (for best results use Spline interpolation). The Developer Zone Example Program in the related links section shows an alternative way to accomplish resampling.

Related Links:
KnowledgeBase 39BCDJMV: Determining the Actual Sample Rate of an Acquisition in NI-DAQmx
KnowledgeBase 27R8Q3YF: How Is the Actual Scan Rate Determined When I Specify the Scan Rate for My Data Acquisition?
Product Page: NI USB-9233
Product Page: NI USB-9234
Product Page: NI USB-9237
Product Manuals: NI 9237 User Guide and Specifications
Product Manuals: NI 9234 User Guide and Specifications
Product Manuals: NI 9233 User Guide and Specifications
NI Developer Zone: Converting Waveform Sampling Rates

Attachments:


- img.JPG - resample.JPG
- sampling rates.PNG



Report Date: 12/21/2005
Last Updated: 01/15/2010
Document ID: 3SKAB1LA

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