Lock-In Amplifier using Red Pitaya

[Gerotero]

Hello everyone!

I am quite new using LabView (just 3 months) because I need it for a project, I am trying to include a Lock-in Amplifier in my LabView program, the main purpose of it is to get the thermal radiation which is emitted from a melted surface which is being cut by a laser, i am using a photoelastic modulator in order to change the state of polarization of the beam in order to analyse it after the cut.

The thermal radiation is going to have low amplitude and huge noise on the signal, so one of the best solutions that I have found is to include a LIA in the program.

The acquisition card that I am using is the Red Pitaya (it allows 125 MS/s with a buffer length of 16384).

The sum of the program is:

- Configuration of the acquisition parameters of the card

- Tratment of the data in order to get the power spectrum and the signal in the time domain

- Prefilter of the signal and creation of the reference signals

- Amplification of the signal and removal of the high frequency generated (twice the original) for getting the original one without noise on it.

The file is attached to the message, I saved it for LabView 2013

All the help will be welcome, and if I made some mistakes (which is highly likely), don't hesitate in correcting it

Thanks a lot in advance!

[stockson]

Hi Gerotero,

is there a specific question or problem you have?

Can you post all the software (drivers, toolkits etc.) necessary to run your program?

[Gerotero]

Hello once more!

Yes I have a question but I didn't ask it, I just explain all the situation, my question is how I could include a filter in Labview which allows me to remove the new frequency of the signal (the one that I obtain when I multiply the original signal by the reference that I generate, which is twice the frequency of the one that I acquire with the Red Pitaya)

I am acquiring two different signals, one of 80 kHz and the other one of 160 Khz, after the multiplication of each signal by their references I obtain two new signals with 160 and 320 kHz and I would like to include a filter in order to get the signals at their original frequencies, for that I have tried by using  Chevyshev and Butterworth bandpass filters (order between 3 and 5) and selecting the frequencies lower upper (60-100 kHz for the 80 kHz signal and 140-180 kHz for the other one). I thought that with these filters I could remove the higher frequency that I include in the signals and get the shape and frequency of the original one with lees noise, but it doesn't work as I expected.

In relation with the drivers and the toolhits that I have used, I have used the package of Labview 2015 and I've just included a Driver that allows to work with the card (Red Pitaya) in Labview, you can download it at the bottom of this website http://redpitaya.com/control/ .

However this card works similarly than other NI cards, the main diference is that you have to include some boxes at the beginning of your file to configurate the data acquisition.

It is possible that you may also need to install a software called PuTTy, in order to configure an SCPI server to be able to use the red pitaya with labview, but It is also explained on the above link.

Thanks once more for your time and attention.

Yours sincerely,

Germán

[Henrik_Volkers]

If the need information is the amplitude (and phase) of a sine you should try the tone detection vi, it's quite powerfull to create a small band filter (pass or stop). Since it is DFT based, you get better results if you apply signals with more than 10 periodes of interest.