# FieldPoint Family

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## How to compute FFT for the output of FP read.vi?

I'm using the field point FP-2000 and FP-AI-100 for signal processing in lab, but i'm confused about how to do the FFT for the output of FP read.vi?

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## Re: How to compute FFT for the output of FP read.vi?

Hi!

When you perform a FP read on a FP-AI-100, specifying all channels in FP IO point, you should get an array of double, which contains all the eight channels.  You should perform the reading of a single channel, and then build an array of values read at that channel through time.  Then, you use this array as input of FFT function.

Try, and if you have further questions post your code, then it'll be easyer to help you!

As a further step, consider to clock someway your sampling, otherwise you'll likeky have a asynchronous sampling, since this hardware doesn't have a clocked sampling process, just sample as fast as possible (max all channel update rate: 360 Hz)

graziano

PS.: I'm really sorry, I don't have that hardware, only have DI, DO, so I can't actually test...

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## Re: How to compute FFT for the output of FP read.vi?

Hi,graziano,

I'm a rookie for using Labview and FPs. The whole process is sampling a signal (about 50Hz) from only one channel of FP-AI-100, and then do the FFT for the output. I've made a code to perform, the sampling rate however is too low and the FFT is not the expect result. Can you give me some specified advice for how to adjust sampling by code and how to do FFT for that.

Guaner

PS:I post my code which name is Test.vi.

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## Re: How to compute FFT for the output of FP read.vi?

Hi Guaner,

I have two problems: I'm not familiar with Datasocket, so I don't know if your VI is correct, and I don't have an analog In module, so that I can't test my VI... I think that what I've written should work, only look at the timings, I suppose that 16 milliseconds is a little too fast for FP-2000, even if update rate is 360 Hz.  You should test the actual speed at which controller can get values from AI module.

Also, please post the FFT you obtained, in which sense it is not as expected?

graziano

Message Edited by Graziano on 09-04-2008 02:07 AM
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## Re: How to compute FFT for the output of FP read.vi?

Hi Guaner,

AI-100 update rate is 2.8ms which means there is not point in running the loop better than this. Also to get a 50Hz signal correctly, idealy you should be sampling at 250 Samples per second. Also there is the throughput rate which will decide how fast the data will be available through network.Are you running the code on windows or on the FP-2000 controller. You will get better results if you run the code on the FP-2000 controller (RT).

------

"A VI inside a Class is worth hundreds in the bush"
യവന്‍ പുലിയാണു കേട്ടാ!!!
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