Issue with phase locked loop instability

[Ringding]

The reference is a square wave, generated by the optical chopper in the measurement system.   It is a good clean and stable signal.  Is the fact that it is a square wave an issue?

The measured signal is derived from the reference and does vary in amplitude and phase.  There is definitely a phase offset between the two, caused by processing in the optical equipment that generates it.  However, I think that this phase offset probably stays pretty constant over multiple measurements.

I'm using V8.20 of LabView.

The output I require is the 'r' component of the 'r,theta' output.  I'm trying to quantify the amount of optical through put for an object at various positions in the field of view of the sensor.  Once I'm outside the usual field of view there is still some signal, caused by scatter in the optics, but this is at a very low level, hence wanting to use a LIA to pull that signal amplitude out of the noise.

Thanks for your help.

[Coq_Rouge]

Hi

In most of my work with lock-in related applications I do AC impedance measurements. And I only need the phase sensitive detector part. I have even built such applications with a sound card. All I know about optical measurements can fit into a fingernail. But in your case I think the PLL is needed. I can not help you more with your problem.

[Ringding]

Thanks for your help.

[orob]

I am intrigued with the sound card lock-in idea.  I see that a design contest was submitted by someone in Vietnam 5 years ago.  Has anyone actually made it work?  Is there an example VI or a methodology that I could use to make my own for a sensor measurement?  I have some ideas on what I want it to do, but I don't have the base to start it off.  Any help would be appreciated.