Signal Conditioning

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Using two filters to remove noise of 60 Hz and above,U

Hello Everyone,


Well i am having a problem filtering the signals. I am new to Labview as well. 

Recently i bought the following parts to measure strain from a wheatstone bridge.

1. cDAQ-9171, CompactDAQ Chassis (1 slot USB)

2. NI 9237 w/ DSUB, 4 Ch , 50 ks/s per Ch, Analog Input module

3. Ni 9923 Front-mount terminal block for 37 pin D sub Modules


But right now for a starter i am trying to measure a strain from permanent magnet vibration shaker from ling dynamic system. 


There is a lot of noise in the signal. So when i use fft i could see frequencies only in imaginary plot of fft . Just 1 spike near zero in the real plot.  Can you let me know why?


Also since i could see 60hz signal in different harmonics of 120 and 180 hz in the imaginary plot. So i used the butterworth filter from filter vi. I used two of them . One as a low pass filter that has cutoff at 100 Hz and another as bandstop filter with cutoff between 58-63 hz. But the result of applying two filters is more distorted than using only one filter.


From the first filter i could see some improvement in the signal, But the fft of the filtered signal does not make sense. Can you please help me find out what is wrong with my vi?


I have included my vi along with this query.


Any suggestions and advice are most welcome and appreciated,







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Hello Sachet,


Please give us more information on how you have DAQ Assistant set up.  

Jonathan R.
Applications Engineer
National Instruments
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