Filter express Vi and signal express Vi's

[shjukheter]

Hi,

          I have signal from USB 6008 that I would like to pass it through highpass filter(FIR equiripple filter). DAQ Assistance given out a dynamic data wire which can connect to different filter VI's. I.e..

1) I can take express filter VI to use as high pass but I did not see equiripple option in it.

2) I can convert the Dynamic data type into array by using Convert from Dynamic Data Express VI and then I can use one of VI in SIgnal express pallet for the same thing.

Here, I am confused about which way can I proceed or i am totally wrong with my procedure. Hope someone clear my issue.

[Oli.P]

Hi Shjukheter,

I'm Oli and I work at National Instruments UK.

I understand that you are having problems connecting your dynamic output from the DAQ Assistant Express VI to the correct filter and that you are unable to find the desired filter within the Express Filter VI.

As you have noticed, there is no option for an equi-ripple highpass filter within the Filters Express VI.  However, there are other VIs that will allow you to perform the desired filter.

You can use either of the following:

'Equi-Ripple HighPass.vi' which can be found in your functions pallette under Signal Processing > Filters.  You will still need to convert your Dynamic Data Type to an Array, but LabVIEW will do this for you.

'DFD Classical Design.vi' which can be found in Signal Processing > Digital Filter Design > Filter Design > Classical Filter.  This does not perform the filter directly, but designs it for you.  If you check the Help file, there is a good example that you can view.

I hope that should clear things up for you.  If there is anything else I can assist you with regarding this issue, please don't hesitate to post.

Regards,

[shjukheter]

Thank you and I have one more doubt that can I do it the same thing as below model.

DAQ Assistance(Dynamic data wire)---> Convert from Dynamic Data Express VI (into array)--->Signal express pallet----> highpass filter(FIR equiripple filter).

Can I go with above. Please comment.

[Oli.P]

Hi,

Sorry for the delayed reply.

The model you have suggested is correct.  I've checked in LabVIEW and the VI performs as I would expect.

If there's anything else, let me know.

Regards,

[shjukheter]

I really sorry to post again here because I posted my doubt here http://forums.ni.com/t5/LabVIEW/Noise-frequencies-elimination/m-p/1714260#M604844. But no one answered. After this highpass filter I would get one signal and I would like to calculate the power of signal(not power spectrum). I have done the same thing In matlab by using the formula that I have specified in above link. Can you help me, how can I find the power(scalar value) of a signal after highpass.

[Oli.P]

Hi Shjukheter,

I've had another look into your issue.

The alternative (in LabVIEW) to Power Spectrum analysis is Power Spectral Density (PSD) analysis.  This describes the how the power of a signal is distributed with frequency.  With an abstract signal, it is defined as the squared value of the signal or the actual power (in watts) dissipated in a load if the signal were a voltage applied across the load.  I think this is probably what you are looking for.

If you use the Spectral Measurements VI (Express > Signal Analysis > Spectral) and select Power spectral density as the Selected Measurement, the output graph will show you the PSD peaks, which is equivalent to the actual power of the signal at various frequencies.

Alternatively, you can try using the FFT Power Spectrum and PSD VI (Programming > Waveform > Analogue Waveform > Waveform Measurements).

That should give you the same outputs as you were getting from Matlab before.

Let me know if there's anything else I can assist you with.

Regards,

[shjukheter]

Oh! Always, every one is discussing about power sprectrum(PSD, it will give vector as output) but indeed i need to calculate te power of a signal(You can see the formula for that in my link above i.e. (Integration(squr of signal))/total time) which will a scalar value in watt.

Anyway, I had done it in below way but i am not sure whether it is right or wrong. See the below picture. I will check it later on this day.

[Oli.P]

Hi Shjukheter,

The code that you have posted calculates the Mean Integrated Square of the input array correctly.  Presumably you are trying to calculate the average power across the frequency range to give you the scalar value for power that is required.

Would you be able to post more or all of your current code so that I can see exactly what you are trying to output?

Regards,