How to define the frequency resolution after FFT transform?

[happybird]

Hellow! Anyone tell me how to define the frequency resolution in FFT transform? thanks!

[rpursley8]

By how long your sample time is. If you sample 1 second of data, your frequency resolution will be 1 Hz, 100 ms -> 10 Hz.

[happybird]

thank,but how to define the frequency range? for example,if my data has 10 seconds long,then what my maximum frequency?

[rpursley8]

Your maximum frequency is half of your sampling rate.

[rpursley8]

Remember the FFT contains both positive and negative frequencies, so if your sampling rate is 1000 Hz, the FFT frequency range is -500 Hz to 500 Hz

[alipio]

Hello

Please, take a look at this tutorial about FFT:
http://zone.ni.com/devzone/conceptd.nsf/2d17d611efb58b22862567a9006ffe76/c045a890751303a6862568650061ea98?OpenDocument

Probably it will help you .
Greetings
Alipio

[Philip_Courtois]

The new NI Measurement Fundamentals series also cover this topic in a higher level tutorial:

Analog Sampling Basics