Lock-in-Amplifier

[gohar]

Hi All,

I'm using DAQ boards ( PCI-6251,PCI-6259) to collect voltage on series of electrodes that are attached on a phantom. A current is injected to a pair of electrodes and is passing through the conductive solution inside of the phantom which will induce voltage to the rest of electrodes ( EIT application).I would like to extract the magnitude and phase of the induced voltage which is a sinusoidal signal that is buried in noise ( The phantom is suppose to be inside of MRI machine). I know that the Lock-In Amplifier in LabView can do this, but I wonder how I can do it with the type of data acquisition hardwares which I have.( I know LabView recommend DAQ board such as NI 4472; but I'm going to use those DAQ boards as one channel at a time it means I'm collecting one channel at a time ( no sequential mode)). In this way the each channel can be sampled as high as 1.25 MS/s. Also, I know my DAQ boards do not have built-in anti-aliasing filters , should I inserte anti-aliasing filter into the signal path ( analogue filter)?if so, should be in all of channels (48). or  Can I use LabView  to do the anti-aliasing instead of analogue filtering?  

I would appreciate any help. 

Regards,

Mehran

[Ryan_V[DE]]

Mehran,

Anti-aliasing must always be done in hardware, not software. In order to minimize the phase error between the reference signal and your measured signal, you will need to sample each on a separate DAQ card. This can be done using the shipping example Multi-Device Synch-Analog Input-Cont Acquisition.vi. It can be found in LabVIEW's example finder under Hardware Input and Output->DAQmx->Synchronization->Multi-Device. One measurement will correspond to your measured signal, and one will correspond to the reference. The following KnowledgeBase articles may provide some additional information on this toolkit:

http://digital.ni.com/public.nsf/websearch/BDBD11147752A45786256C2A004FC898?OpenDocument

http://digital.ni.com/public.nsf/websearch/0DF72DBB9811E7A586256F80006B9710?OpenDocument

http://digital.ni.com/public.nsf/websearch/EBAADBD271ADFEC586256C86007B63F9?OpenDocument

Please let me know if you have any additional questions.


Hope this helps,
Ryan V.