How to get spectral analysis of 1D array of waveform ?

[JP187]

Hi,

I am measuring output of 4 strain gauges using NITB-4330 front block mounted on a NI-PXIe-1073 chasis. When i used the output of DAQmx Read to get spectral analysis, it did't show any results. I thinks, it has something to do with data type. One more problem is, i am getting error-20023 for filtering even though my cutoff frequency is less than half of the sampling frequency. Can anyone please tell me what am i doing wrong and how can i solve these problems?

Please refer the attached VI, image and following specification for more information.

Bridge Configuration: Full bridge

Excitaion Source: Internal

Excitaion Value: 2.5 volts

Bridge Resistance: 350 Ohm

Max. Value: 25

Min. Value: -25

Units: mV/V

Sample Mode: Continuous Samples

Sample Rate: 100 Hz

Source: Onboard clock

Thanks in advance.

Regards,

JP

[GerdW]

Hi JP,

using your filter expressVI with a simulated waveform with 1kHz samplerate works fine:

(You used 1000Hz as samplerate in your VI and I even made an array from that single waveform as in your VI.)

So it seems you are doing something different in your VI. But as you don't supply any (default) data with your VI I cannot help much more than this…

[JP187]

Hi GerdW,

I used filter express VI to get rid of noise from my original signal. But my filtered signal looks different than it supposed to be (though there is some noise reduction). It's like inverse of the original signal. How can i solve this problem? And can you please tell me how can i calulate signal to noise ratio in labview?

[GerdW]

Hi JP,

how do you want to judge on those filter when you plot only one of 100 samples per iteration of both your signal and the filtered result?

General advice: getting rid of ExpressVIs does really help to learn and understand which data are used in your VI. Hiding everything in bluish DDT wires is bad…

[JP187]

Hi GerdW,

thanks for the advice. I am trying to have labview programm without express VIs. One of my concern is, original and filtered signal have more or less same amplitude (you can see that in image i previously attached). Filtered signal supposed to have less amplitude than original signal.

Regards,

JP