Frequency resolution of NI 9234

[marcos88]

Hello dears,

In the data sheet of NI 9234 (a four-channel dynamic signal acquisition module), it is specified that the data rate range (Fs) mínimum is 1.652 KS/s and the maximum is 51.2 KS/s.

How these data and / or others of the data sheet are linked, with the frequency resolution of the acquirer.

Thank you.

Marcos 

[Kevin_Price]

It's right there at the top of page 6 of the pdf you linked.

Your internal master timebase is 13.1072 MHz.

The master timebase is *always* divided by 256, which gets you to 51.2 kHz.

Then you must further divide by an integer in the range [1,31].

51.2 kHz / n    where n must be an integer from 1 to 31

If you were to supply a different master timebase externally, you'd still have the same rules about dividing first by 256, then by an integer in the [1,31] range.

-Kevin P

[Henrik_Volkers]

Your questions isn't quite clear (to me;) )  about what frequency resolution. The samplerate frequency or the frequency you want to measure?

The samplerate you choose is one part. The next part is how many points you aquire and how much you know about your signal, if you what to measure a frequency. 

The common way to measure a frequency is to use a timer, but if you measure a a periodic analog signal a (sine) fit can give you subsample frequency resolution.

[Cavarval]

Hello Marcos,

In case you mean the frequency resolution in a frequency domain measurement, like an FFT, the following documents should help:

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z0000019MIYSA2&l=en-US

http://zone.ni.com/reference/en-XX/help/370371K-01/smtlvconcepts/guid-cce625b8-0319-465b-b5f7-06f878...

https://zone.ni.com/reference/en-XX/help/373398C-01/svaconcepts/svincreasefreqres/

Sample rate does not affect resolution on its own, but it does indirectly. Frequency resolution is only affected by the measurement time of the signal, however, since the measurement time is given as the ratio of the number of samples acquired and the sample rate. 

What sample rate defines directly is what is the largest frequency you can acquire. In an FFT, for a given sample rate, you can increase the resolution by acquiring more samples, hence increasing the measurement time.

Does this help?