I don't know why Frequency is difference.

[Jarvis90N]

Hi, I measure 20kHz signal by using USB-4432 and NI 9232.

Spectral analysis is performed after data acquisition. USB-4432 is 20143 Hz and NI 9232 is 19670 Hz result.

It is same sampling rate and same resolution. But Frequency is difference.

so, I wonder Why the frequency is different between USB-4432 and NI 9232.

Is there anyone who can explain this issue?

Thank you for your reply

[dsb@NI]

Generally, we can be more help when you post your code with your question.

I will venture a guess that you specified a sample rate of 50 kHz. The 9232 coerced that sample rate to 51.2 kHz. Likely, your code used the specified rate of 50 kHz to calculate dt of the acquired waveform. Use the actual sample rate instead, or use the waveform instance of DAQmx Read, and DAQmx will automatically build the waveform with correct timing information.

Note, the 4432 uses a different technology to generate the sample clock and does not coerce the sample rate noticeably.

You started your post by saying that you measured a 20 kHz signal. What did you use to generate that signal? How accurate is the generator frequency?

[Jarvis90]

A 20 kHz signal is a constant signal from other equipment.

so..you say that NI 9232 coerced to 51.2kHz and USB 4432 is 50kHz ??

I will venture a guess that CompactDAQ Internal Timebase is 13.1072MHz and USB 4432 is 48MHz.

Is there any problem with this?

[dsb@NI]

It is only a problem if the assumed sample rate yields an unexpected frequency ; )

I don't know what you are trying to accomplish, so it is difficult to provide more directed guidance.