Filtering with Butterworth

[Soran]

Hi everyone,

I have been trying to use Butterworth as a lowpass filter to limit the frequanies of my signal. I have provided the attached code in which two simple sine waves with 2Hz and 10Hz frequencies have been added. I have used low pass Butterworth filter with 4Hz as low cut of frequency. I expected to have the sine signal with frequency=2Hz (2<4<10) but the output of the filter (and also its FFT) is a very ugly!! and weird signal. Would anyone please help me to figure out where my mistake is and how to solve this problem?

Thank you,

Soran

[johnsold · Accepted solution]

Soran,

The default values on your controls do not match the settings of the SImulate Signal VIs, specifically the sampling rate. When I set the sampling freq control to 250, everything seems fine.

Creating a waveform to tell the second FFT Power Spectrum VI about the timing information will give suitably scaled graphs for the filtered signals. Note that Spectrum Y-axes are set to logarithmic mapping in the image below.

Lynn

[Soran]

Thank you so much Lynn. It was very helpful.

Soran