Peak frequency

[Binoldino]

Hello,

I would like to find out where I have a Peak Frequencies in my measurement. I have a sample rate of 1Hz (RS232).

How can I do that? Is that possible with LabVIEW 8.2.1 Full version?

And how to find out what are the highest possible frequency? Spectral Analyise?

Thanks

Binoldino

[mikeporter]

The highest possible frequency is the maximum frequency that will pass through your anti-aliasing filter (you do HAVE an anti-aliasing filter right?). You see the problem is that without a filter to bandlimit the input signal the best I can tell you is what frequency you can reproduce accurately - which is 0.5 Hz (1/2 sample rate). Without bandlimiting every thing from .5 Hz to light (ok, "light" is a bit of an exaggeration) will still be in the data but it will be aliased into the gap between DC and 0.5Hz.

In terms of the frequency domain representation of the data, yes you can do that with the full version. Check out the FFT examples that ship with LV.

Mike...

[Binoldino]

If I have a frequency under 0.5Hz, than I won't have any problem, but if not. First I have to find out what is my highest frequency?

How can I do that? (maybe I don't understand it in the moment, sorry)

[mikeporter]

Can you tell me a bit about your application. What is it that you're measuring?

Mike...

[Binoldino]

Sorry for my delay!

I measure the weight of press felts, that is a base which is woven of yarn and needled together with different kind of fibers. I measure this felt 2 times in the length direction, that means about 800 to 1600 measured data.

So now after the measurement I would like to analyise this data, where there are the peak frequencies.

I measure this data with a gamma backscatter sensor and send this to a device which convert the signal to g/m2. This device is connected with RS232 to a PC. The sample rate is 1Hz.

Hmm, do you need more?

Many thanks!

[mikeporter]

Ok, I think I see the issue. You are measuring the density of this material and are wanting to generate a histogram of the measurements to determine how much variation there is in the material's density. Is this correct?

The analysis tools in the full version of LV can perform this calculation for you. Do a search in the examples for histogram and you'll find several examples you can try out and modify as needed.

Mike...