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Down sampling in delta sigma module NI 9242

 

Hello Community,

I am trying to acquire the data from Delta-Sigma NI 9242 module, which has 50ks/s to 1.613 Ks/s, (1000 samples/ cycle to 32.23 samples/cycle). I want to 12 samples/ cycles to 72 samples/cycle. How can I configure it?

Also, if you are suggesting decimation. Please provide some help regarding this.

 

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Your ultimate sampling should be an integer number of samples of one of the sample rates available on that type of module (delta-sigma ADC). So you could choose one of the sampling rates, and then subsample to give something close to your required 12-72 samples/cylce - but it is unlikely you will get exactly those two rates. The higher the module sample rate used and higher subsampling rates will allow it to be as close as it can be. Also, if helpful you could do something useful (like filtering) on the original higher sample rate to improve the measurement.

 

Alternatively change to a SAR type ADC and you get the flexibility of being able to set the sample rate to what you want.

 

Consultant Control Engineer
www-isc-ltd.com
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I Don't have SAR type ADC. I have only Delta-Sigma ADC.

Can you provide some help on "how can I do subsampling using filtering".

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It can be as simple as picking every Nth sample from the original, so if you start with something that is 5KHz and take every 25th sample you end up with a sampled signal at 200Hz. There is a decimate function that does this - see here.

 

As I said rather than just throwing away those other data points you could do something more useful like filtering, and that may be important to do if aliasing could potentially corrupt the new signal.

Consultant Control Engineer
www-isc-ltd.com
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