Measure THD from 20Hz to 1KHz

[DavidDLC]

Hi to all, 

We are using a NI USB-6281, to capture a 100 Hz tone, with a sampling rate of 625KS/s and we are capturing 325K samples. We have the low pass filter on the card on.

We want to measure the THD from 20Hz to 1KHz only, how can we do this ?

How can we extract this information (20Hz to 1KHz) before feeding it to the THD analyzer ?

Any help is really appreciated.

David.

[William1225]

Sounds like the bandpass filter can be used, but I thought you should know it, so I'm wondering why not put a bandpass filter before the THD measurement?

[DavidDLC]

Yes thank you for your help, I just found the Digital FIR Filter, I will give it a try.

[DavidDLC]

I used the bandpass filter from 20 Hz to 1 KHz, but when running FFT it still shows me information from 0 to Nyquist (312.5K), how can I just pass information from 20Hz to 1KHz to the FFT and the THD ?

I want to run the FFT and just have the information from 20Hz to 1KHz and to have the THD VI just to process that information

David. 

[RavensFan]

Take a subset of the FFT array.