How can I get the DC component out of a signal in Labview

[lcz]

I was trying to get the DC component of a signal using lowpass filters provided by Labview(professional version 8.2). I used the FIR windowed filter but I couldn't get what I expected. The sample rate is 20* the maxium signal frequency. I simulated a function like y= 10(volt)+Sin(2*pi*f*t+phase). If I set the low cutoff to be less than the frequency f, shouldn't I get 10 volt as the outputs?  See the attachment for vi. Thanks!

[BenjaminR]

Hi,

You can use the filters located in Signal Processing -> Filters, then create a constant from the "filter type" input and select "Lowpass". There is also an AC & DC estimator vi, located in: Signal Processing -> Measurement.

You may also use something like "running mean" filter. To do it you need to calculate the mean value in some range around every point. It will decrease the value of the noise and will give you the dc value (or slow changing part) of your signal. Finally you can use median filter.

[lcz]

Thanks Ben.

I tried the Average DC-RMS.vi under Signal Processing -> Measurement. It works pretty well. Thank you.

By the way, your vi is writen in 8.5 I couldn't open it in 8.2.

Chen