NI9235/9236 default hardware sample rate when under scan mode.

[tarzanyu]

Hi

I am currently using NI9235 with cRIO under scan mode, which allows the sample rate up to 500Hz. I do realize that the module card has 12.8MHz internal timebase and under the FPGA mode, the software and hardware combined anti-aliasing filter will be adjusted automatically according to the data rate setup, which is one of set of values from 10KHz to 794Hz. Unfortunately, I don't have the FPGA package at the moment.

My question is that what the hardware data rate will be, if NI9235 samples at 500Hz under the scan mode. Does the anti-aliasing filter still work at little below the half of the hardware data rate?

Marco

BMT WBM

[enderWiggin10]

Hi Marco,

What do you mean by the hardware rate?  Sample rate (how many smaples are taken per second) or data rate(number of samples per second multiplied by the data size-24 bit)?  The anti-aliasing filter is a hardware filter built in that filter out signal below 1/2 of the sampling frequency, which should be fixed.

Does this help?

Best,

[enderWiggin10]

Hi Marco,

Also, I am not 100% sure how the scan engine works as I typically use the module in a compact DAQ environment.  I am not sure that you would want to use the DSA module with scan engine on the RIO, but rather it would be better to use FPGA.  I would imagine you would want to use the DSA module to its full functionality of its sample clock and resolution, which would not be achievable using scan mode.

Perhaps I am incorrect, but could you then fill me in on the application you are achieving, and why you are desiring to use the module in scan mode?

Best,

[tarzanyu]

Hi Adam

Thanks for your quick reply.

I don't have the licensed FPGA at the moment, so scan mode is the only option right now.

The hardware sample rate refers to the data acquisition speed of the NI9235, which normally can be selected through a drop-list of the properties window under FPGA.

The scan mode period (>=2ms) works like a software desampling. If the 9235 samples at highest 10KHz, I definitely need to program the anti-aliasing filtering after the scanned 500Hz data. But if the 9235 does the sampling at lowest 794Hz, I maybe can skip the filtering if there is not too much noise between 250Hz and 397Hz.

I am doing some intensive real-time fatigue calculation using the cRIO, so the CPU is quite close to its full capacity, and the filtering can be a another pusher.

Regards,

Marco

[speleato · Accepted solution]

Hello Marco,

When used in scan mode the 9235 and 9236 are configured to sample at 10 KHz.  That setting is, unfortunately, not user configurable in scan mode.

Let me know if you have any other questions.

Sebastian

[tarzanyu]

Thanks Sebastian

Just want to double confirm that the hardware anti-aliasing filter will still work below 5 KHz under scan mode.

Marco