cRIO external timebase for NI 9232

[charlie87]

Hi,

I am using cRIO and AD module NI9232. I want to change my sample rate under the minimal value which is supported by internal timebase 13 MHz. NI9232 should support external timebase according to the specification. But I cannot find the way how to set different external timebase. Do you know how ? 

Another question is ... When I change somehow the external timebase and my data rates gona be different -> does filter setting change ? I mean if aliasing filter is working with external timebase...

[Zody]

Hello,

Well, the clock is very easy to be shared in the same chassis from another Delta-Sigma module.

For example, if you have a 9229 which has a timebase clock of 12.8MHz, this can be shared to 9232 and in this way you will force 9232 to have the sampling rate of 9229.

In order to share the clock, you will go in LV project, right click on 9229 module, properties, and you can click "export onboard clock".

Than you will go to 9232, right click -> properties and choose for Master Timebase source, the clock that you just exported. It will pop a warning telling you that the master base clock is shared from another module

The minimum sampling frequency you can have with this clock is 1.6113 KS/s

What sampling rate are you interested in?

Kind regards,

Ion R.

[charlie87]

I see. I thought that I can generate some external timebase directly in FPGA (derived from FPGA clock) not from another NI module. I am interested in changing sampling frequency from max 102400Hz to very low about a few Hz.

Now I am ''manualy 'decimating signal using case scructure and some overhead to get so low frequency...

[Zody]

Hello,

As far as I know, this is the only way to do it, you can just import from another module.

And in your case, yes, decimation will be the solution.

Kind regards,

Ion R.

[ba_0101]

What is the best way to decimate and ensure that no data is aliased? Is there a resample/decimate VI that filters data before decimating?

[charlie87]

There is rational resampler VI  with anti-aliasing filter.