NI9234 Filter

[MathieuSG]

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.

 

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.

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 

[ajangot]

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, 

[MathieuSG]

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