Using Fir filter in Labview

[Tinafan]

Hi guys,

     I generated two singals, their frequencies are 1HZ and 10HZ. The amplitude of the two signals is 1 . Now I want to remove the 10HZ signal, and I choose the FIR Windowed Filter PtByPt.vi .The result was not so ideally, the assigned value of the filtered signal should be 1, but it wasn't . What's wrong ?  Can you help  me? Thanks in advance.signal before filtersignal after filter

[GerdW]

Hi Tinafan,

What's wrong ?

Something in your VI…

(Hint: Why does the time scale/ x axis change by filtering the signal?)

 Can you help  me?

Not as long as you don't attach your VI…

[Tinafan]

UdpRevLV.vi  is my main vi,  used to receive datas from MFC.  

The X scale is signal's  period.  ((Hint: Why does the time scale/ x axis change by filtering the signal?) I don't understand your hint)

The correct result is : Filtered signal' amplitude  should be 1, at least  close to 1.  But  mine is not 1.

[IanSh]

I'm not familiar with the data you're getting, but try different values for the low cutoff. Surely this should be between 1-10, not 0.0002? Is the sample rate correct at 10000? These probably have the most impact on the filtered data.

Also, you can replace all your logic for the valid data with an "Add Array Elements" function, the output of which you can just wire to your case structure.

Also, it looks like you are trying to process all the data 4 bytes at a time, however you request a new data packet each time via UDP. Is this what you want to do?

Should you have a stop button for the loop condition? Instead of wiring a false constant to it?

[Tinafan]

I have changed the values of the low cutoff.  And the situation seems turned correct. What is the mean of low cutoff? Or what's the relationship with  sample rate? I set the low cutoff frequency equal to 0.0002,  because I see it as normalized frequency .(2 divided by 10000，  that is my reason.)

My sample rate is 10000,  I am sure.  I use a timer send datas to  my VI  every 10ms one time,  every time send 100 numbers. 

Thank u for your attention ,I will add a stop button in my while loop.