FFT analysis

[taraka]

Hi, As i was very new to labview, i was trying to do FFT anlysis by sending analog signals and collect data from pressure sensore, while  I run my LabVIEW programs using a DAQmx Read VI to Acquiring Data Continuously I get an error That says ERROR : 200279  Measurements: Attempted to read samples That are no longer available. The sample was Requested Previously available, but has since been over written. could please suggest some possible methods to get rid of this i had tried the methods in NI but it dosent work for my code and i had attached the code . could please find sometime to see it and get the possible solution.

Thank you,

Tarka.

[CaravagGIO]

Hi taraka,

it looks your while loop is too slow to read data from buffer fast enough. AI data overwrites the data in DAQ buffer and it produce an error. You can check the input size of buffer and number of elements in buffer using DAQmx property notes. Please find attached snippet of while loop you should run parallel to main loop to see the buffer properties. Just connect the task. You should increase the number of samples you read in while loop to prevent buffer overflow or increase the speed of while loop.

Best regards,

CaravagGIO

[taraka]

Hi, Caravag,

what you said is correct  AI data overwrites the data in DAQ buffer and it produce an error, i had connected the loop which you send and run parllel to the mainloop but  as  i need the frequency from 100 to 80KHz so i have given as start frequency as 100Hz and stop frequency as 80kHz and sampling rate as 160K and when i start running it says that to increase sample  and increase to 12K and even much. but still it shows an same error.

[CaravagGIO]

I tested your vi on simulated card PCI-4461 and I did not obtain the error. I set start freq 100Hz, stop freq 80kHz, and sampling rate 160kS/s and it works. Only thing I changed in your vi was the number of samples per channel readed in DAQmx read vi (2^14).

[taraka]

How it work? Did you connect task which you said regarding buffer. or with out connecting that task?

I was using PCI 6024E card

[CaravagGIO]

I @m not able to obtain that error http://screencast.com/t/7suaJ1j3wjg

I checked time evolution of number of samples in buffer yesterday @nd it h@s a constant trend. Maximum number of samples w@s about 10000.

[taraka]

Hi, Thanks, now i'm able to rum my vi.I need a small information, I'm using a piezoelectric stack  to generate some ultrasound in water to caluclating maximum pressure inside the beaker i'm using, for that i'm using labview Spectrum analysis(FFT) to find the resonance peak. first i'm sending uniform white noise to check where the maximum harmonic  i got  then @ that frequency i'm sending sinewave to get the resonace peak. that what i'm trying to do, but when i send white noise^, sine there is no difference in the FFT spectrum is anything wrong in my vi? 

[CaravagGIO]

[taraka]

Hi, i  canged DAQmx write to "Analog WFM 1 Chan Nsamp" @nd adject the smaples inserted into DAQmx write @nd i  inserted a correct physical channel.

Is there @ny other methods to get ...

[taraka]

Hi CaravagGIO , i had made many changes in my code, then again i encounter the same problem which i got it at first ERROR- 200279 and ERROR-200016

could you please check whether it runs in your computer as like before....,