Lock In Amplifier

[_Tempus_Fugit_]

Hey there!

I am studying electrical engineering. As a task we gotta build a Lock-In-Amplifier in LabVIEW2017. As further information: the Lock-In-Amplifier has to be phase-independent. That is why i multiply my signal with once a sine and once with a cosine. It just has to work with any frequency and amplitude. There is no more specific information. It just has to work.
My problem is, that i don't know how to set up the Equi Ripple Lowpass Filter in the vi attached. Or maybe you can tell me another, different approach on how to solve the task. The output signal isn't what it is supposed to be. Any help would be appreciated. 

Thanks in advance!

[altenbach]

As a first step, you probably should stay away from express VIs and dynamic data. you should also check your settings, because the sine and cosine have 10x more points, which you drop when multiplying. Why do you need to filter? Do you have a more exact problem description?

Maybe this (very remotely related) old discussion can give you some ideas.

[_Tempus_Fugit_]

Thank you for your answer. I will try to stay away from dynamic data. To specify the problem: everything works fine until after the multiplier. I think the lowpass filter is the problem. I think something is set wrong or maybe just a small mistake of mine, but as seen on the graphics the lowpass filter doesn't filter the signal at all. To answer your question: i want to filter the signal because this vi is just a prototype. So I just want to create a sine signal with white noise and want to filter the noise. In reality this vi will be used to filter a real signal and not just one i created. This is why i really need to have the lowpass filter, because this is basically my approach to get a filtered signal with no (i know a bit noise is still going to be left) noise.

[altenbach]

(Sorry, posting by phone, cannot look at code)

A lock-in detector is not for filtering, but for the detection of instantaneous phase and amplitude of a certain frequency component. You would do that over and over to see how it changes over time.

Given that result (phase and amplitude), you can generate the noiseless signal at any time.

I also don't see the purpose of your integrations.

[_Tempus_Fugit_]

That is very helpful information to me! Thank you so much for your help.

[engineer2744]

hi

kindly guide me how should i use the attached for simulated signals

[yangchi1]

can you share your VI， I don't know how to add lock-in PLL， filter, MC，Thank you very much!

[Intaris]

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@altenbach wrote:

(Sorry, posting by phone, cannot look at code)

A lock-in detector is not for filtering, but for the detection of instantaneous phase and amplitude of a certain frequency component. You would do that over and over to see how it changes over time.

Given that result (phase and amplitude), you can generate the noiseless signal at any time.

I also don't see the purpose of your integrations.

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I'm not sure I understand. A lock-in typically incorporates a low-pass filter (or SYNC-Filter) in order to give any kind of meaningful data. Any instantaneous sampling of the result of the multiplication the OP is referring to would include a superimposed signal of twice the frequency of the reference with vastly varying amplitudes depending on the current phase state of the reference signal. This will oscillate wildly, but averaging over one period of the reference signal is normal in lock-in functioning. This can, as mentioned earlier, be either a sync filter (Monitoring the null-crossing of the reference signal) or a low-pass filter which will then have a dual-purpose of filtering out extra noise from the signal.

https://en.wikipedia.org/wiki/Lock-in_amplifier