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NI9234 Filter

Hello,

 

I am using the NI9234 (DSA board), a NI9215 (standard AI board) and a 9263 board (AO)  on a cDAQ system.

 

I use a log chirp as excitation signal (1V pk-pk, from 100Hz to 10kHz, duration :3s, v).I use the SC Chirp Waveform available with the Sound&Vibration Toolkit. The excitation signal is measured by the NI9234 and the NI9215.

The 9234 has IEPE excitation "off". I tried to turn on/off AC/DC filtering but nothing change. Sampling frequency is 51200 Hz.

 

I am surprised about the result(see figures) and I can not explain it, because the passband filter as described in the spec speak about +/- 40mdB, to this is very flat compared with my measurements.

 temporal_NI9234vsNI9215.JPG

 

On the temporal view, we can see that amplitudes measured by the 9215 are coherent with my excitation signal, but it is attenuated with the 9234.

 

PowerSpectrum_NI9234vsNI9215.JPG

As you can see, the signal is progressively attenuated from 3kHz to 10kHz on the spectrum.

 

Could you help me to understand this problem please ?? Is it a hardware problem on my board ??

 

Thanks in advance.

 

Mathieu 

 

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Hi,

 

You have two possibility:

1) Try with an other module to generate your signal. The 9263 module have 100kS/s and you want a waveform at 10Khz so you have only 10S/period, it's maybe not very good. If you can try with a module with more sample by seconde, you maybe don't see the attenuation.

2) The DSA module have a bandwith about 40kHz so try with a GBF or static frequencies and try to have same results.

 

Regards, 

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Hi Aurelien,

 

thanks for your answer.

 

I will try to increase the sampling frequency of the AO but I do not understand why the attenuation can come from the AO board.

In my settings, due to synchronisation needs, I setted the AO sampling frequency on the same FS as on the 9234 board. To do that, I use the DAQmx Trigger.vi and I put the terminal source on "/cDAQ1/ai/SampleClock". Maybe there is a problem with my DAQ configuration.

 

How can I ensure that I 'll have a perfect synchronisation between AO and AI if I set 2 different sampling frequency for each task ??

 

Thanks,

 

Mathieu 

 

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