low-pass filter

[michele1991]

Hello everybody,

Labview novice here. I'm trying to measure some data from a real device (NI USB-9162) and then filtering it with a Butterworth lowpass filter. The measurement seems to work fine but the output of the filter is the same of the unfiltered data. I had a look to several tutorials and discussions but couldn't find a solution to the problem. I'm attaching a screenshot of my code, can anybody help to fix it?

Many thanks in advance!

Michele

[Henrik_Volkers]

You have used the point by point lowpassfilter .. you need to use the one with a wavefm input.   Use the wfrm datatype and the Digital IIR Filter.vi  .

No need to collect the data in the loop, just configure the express save vi and additionally connect the Flush input to the stop button. Otherwise you migth run out of memory during a longer aquisition. 

A sadly classical demonstation of the bad habbist  of the dynamic signal datatype....  

[michele1991]

Thank you Henrik, I finally managed to filter my signal. For what concerns data collection, did you mean to do something like what I'm attaching in the picture? So moving the express save block inside the loop?

Cheers,

Michele

[Henrik_Volkers]

getting better 🙂

see the help for the vis to optimize your power spectrum and filter (INIT)  and have a look at the shipped examples  (Help-find examples)

no need for the wfrm appenders anymore 😄

[michele1991]

thanks again Henrik! You've been really helpful! 🙂

Can I ask you a last question? I need a similar code to acquire some measurement, but this time I need a longer acquisition in time (hours instead of seconds as I was doing previously).

I get this error:

You probably mentioned this already when you were referring to data collection and configuring the express save but I haven't really understood how to do that...

For your better understanding, I attach another picture of my code (it's roughly the same anyway).

Thanks again for your patience.

Cheers,

Michele

[Henrik_Volkers]

No great help with the pictures, a posted vi would allow other to look into the configuration of your expressvi ... (I currently stuck with 2012)

Hint. the error message tells you to increase the buffer and the number of samples to read as a block. double click on the aquisition express vi , read the help, and change the settings.

[michele1991]

Solved again, thanks!!!

Cheers,

Michele