Virtual Lockin Amplifier

[l1k]

Time to publicly display my ignorance concerning lockin amplifiers.  Here'a a little code I'm working to help me figure out how this lockin stuff works.  I know the idea is that if you modulate a noisey signal, you should be able to filter out unwanted noise.  I downloaded the demo, and I'm just trying to simulate some data for a code I need to write down the road.  What now?  Do I run the X, Y, R, Theta arrays through some fitter or filter or something?  I'm not seeing how this all works.  Or, is the X,Y,R, Theta the output?  If it is, uhh... what is that?  Sorry for being dumb...

[Raajit_Lall]

Hello,

I am not sure if you have already looked at the links below but they are a really good resource for Lock In Amplifiers. Specially the NI Lock In Amplifier Start Up Kit. The download has a word document (NI Lockin Amplifier Start Up Kit User Manual) that lists, in detail, all the VIs and subVIs that are used in the kit. It also explains all the demos that are downloaded with the kit. For example, the LockInDemodulator.vi from which you are getting the X,Y,R and Theta has the following description for the "data" output. This document also explains the demonstrations that are downloaded with the kit.

"A 2-D array containing X and Y components of the input signal at the frequency of the reference signal for all filter roll-off values (one per column). Note that all filter stages necessary to obtain different roll-offs are calculated in parallel so that one can pick the output of any stage without paying a “re-settling time” penalty. For more about the topic, please see the Filter."

Best Regards,

Raajit L | Applications Engineer | National Instruments

[pal1977]

Hi ,

 i have a NI DAQ and with that i am getting the signals of a oscilloscope to my computer via a labview program. i was wondering if i can use a labview program which will work as lock in amplifier program?? can it substitute the lock in amplifier completely? IF so is the above lock in amplifier code my labview NI free to use ??

thanks

[Raajit_Lall]

Hello,

If you just click on the Lock-In Amplifier link you will be able to download the free Amplifier, which comes with Demos that you might find helpful. And yes, this software is free for you to download. You can then use the VIs in your existing code. Details on all the functions and subVIs can be found in the word document that is downloaded with the startup kit.

Regards,

Raajit L

Message Edited by Raajit L on 03-05-2007 07:21 PM

[NFSMW]

Hi, Raajit L,

Your information is very useful! Could I have two question for you? 

First thing I would like to know is that how can we decide or choose a Lock-in amplifier? Operating frequency range? voltage sensitivity? current sensitivity? time constants? etc. What kind of parameter and characteristics we have to compare between two different Lock-in amplifier??

Secondly, what is the limitations (characteristics) of this Virtual Lock-in Amplifier? What is the operating frequency range? what is the sensitivity of voltage and current?

I am new to Lock-in amplifier and try to find something suitble to me and this NI Virtual Lock-in amplifier is amazing. So, hopefully you can help me to answer my questions above then I can try to decide to pick up commercial big box or using this wonderful PC running beauty. Thank you!! 🙂

[Urs Bögli]

NFSMW schrieb:
> Hi, Raajit L,
>  
> Your information is very useful! Could I have two question for you? 
>  
> First thing I would like to know is that how can we decide or choose a Lock-in amplifier? Operating frequency range? voltage sensitivity? current sensitivity? time constants? etc. What kind of parameter and characteristics we have to compare between two different Lock-in amplifier??
>  
> Secondly, what is the limitations (characteristics) of this Virtual Lock-in Amplifier? What is the operating frequency range? what is the sensitivity of voltage and current?
>  
> I am new to Lock-in amplifier and try to find something suitble to me and this NI Virtual Lock-in amplifier is amazing. So, hopefully you can help me to answer my questions above then I can try to decide to pick up commercial big box or using this wonderful PC running beauty. Thank you!! :-)

Download and study the handbook of a good Lock-In like

http://www.thinksrs.com/products/SR810830.htm

Have a look at
http://www.lockin.de/

It is not so difficult to write a Lock-in in Labview after you have
understood the ideas!

Good Luck

[l1k]

I have to admit, I'm still confused.  I would like to play with the demo, because I am pretty sure this is the type of thing I need to do.  There are several sub-VI's that I don't have that make using the demo impossible.  Specifically:

AI Config.vi
AI Start.vi
AI Read.vi
Simulate_Data.vi
AI Clear.vi

I think that's it. Does anyone know what AI stands for (artificial intelligence?)and can I replace these vi's with anything that's preinstalled into LabView 8.2?  Or better yet, can I download these vi's somewhere?  Thanks a lot,

Laura

[Raajit_Lall]

Hi Laura,

It looks like you do not have the Traditional DAQ driver installed.  Those VIs are all included with the Traditional DAQ driver. AI, in this case stands for Analog Input

Regards,

[NANONFSMW]

Hi, Raajit L,

May I borrow some of your time? The attachment is something I wrote to exam MultiChannelLockin.vi. I used two Simulate Signal VIs to generate a Square waveform (1KHz, 0.2 amplitude) as Ref to LIA and a Sine Wave (1KHz, 2 amplitude) with Uniform White Noise (100 amplitude) to be a signal.

My questions:

(1)Am I programing this VI correctly? If not, the following questions are non-sense, and please let me know what's wrong with my programing. Thank you!

If my VI was correct, then,

(2)In my opinion, I should be able to get the sinewave signal out of the 100 amplitude noise, and the R value would be 2. Am I saying it right? I did get varied value around 2, from 1.8 to 2.3. But shouldn't I get a stable value as 2?

(3)The value of frequency I got is quite weird as well, when I tried to use only Square and Sine in 1KHz without any adding noise, the frequency shows 2048Hz, I thought it should be 1000Hz, am I right?

The general setup of this LIA is:

Sample rate:102400Hz; PLL TC: 0.1S, FIR filter with TC=1S, 20dB rolloff, first order.

Thank you very much! I really appreciate this!

[kmous]

Hello Pal ,
I looking for the same programe u have , a program that gets the signals of a oscilloscope to my computer via a labview program.
have u done it ? if yes plz let me know 🙂
Thank you