Filter PtByPt issue

[yamelbio]

I am using a point by point low pass filter (butterworth) everything works well but what happens is that the direct component of the signal is attenuated a lot when a low pass filter should leave it intact, I send you a photo of the program (one I did to see the specific problem is not the original).

 

With a cutoff frequency of 40Hz look at the big difference between the white signal (unfiltered) and the red signal (filtered).

 

Virtually the signal does not change in time, its almos a component of DC. And even so it attenuates a lot ...

Thanks for everything!!

 

[RavensFan]

Do you have a question here?

Can you attach real screenshots and a VI rather than difficult to see pictures of your monitor?

What is your loop rate?

Because the pt. by pt. is working with a scalar value and no timing information, it will assume the numbers are coming it at 1 Hz, even if your loop is running faster.

[yamelbio]

I am really sorry for that bad quality pics...

Screenshoots:

 

  I have attached the vi.

The question is: why if I have just a DC component, the signal is being reduced that way by a lowpass filter? I am missing something?

Thanks again.

[PsyenceFact · Accepted solution]

Hi yamelbio,

You have the initialize terminal of the Butterworth filter set permanently to TRUE so the internal state of the filter is being reset with every pass.  You should only initialize in the first pass through the loop: check the loop iteration value with Equal To 0? and pass the boolean result to the initialize terminal.

PsyenceFact

[yamelbio]

I realized of that 5 minutes ago and I feel really stupid right now!! 

Thank you very much!

I was stucked for nothing...

Greethings from Cuba!

[MalekLam]

Hi

I have the same problem but I was able to solve you can explain again

[altenbach]

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@MalekLam wrote:

I have the same problem but I was able to solve you can explain again

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Why do you need an explanation if you were able to solve the problem?

[MalekLam]

I did not pay attention I will I was not able to solve the problem but good now I solved the problem thank you