Lock In Amplifier set up - help required please

[Ringding]

Hi,

I am running some experiments in the lab that require a LIA to pull out the signal at low S:N levels.  I'm capturing the data (25kS/s) and writing to a TDMS file to allow me to post process the data.  I'm capturing two channels, the data signal and a reference signal (from the optical chopper in the experiment).  The reference is at 800Hz and the signal is almost sinusoidal but of varying amplitude depending on measurement point.

With help I have transformed the 1D waveform array from the TDMS file into a 2D array and input it to the LIA (please see attached).  I'm fairly happy with the setup of the PLL.  The fr feedback returns between 750Hz and 800Hz (depending on how long a sample I use, currently 0.05s so approimately 40 cycles of signal).  However, I'm getting no output from the LIA.  I wonder if my setup of the filter is incorrect?

Perhaps you could give some advice.

TIA.

[Ringding]

I should have added that I'm interested in only the R component of the R,theta output of the LIA.

The data was captured using a 6143-S card.

There is a lag of approximately 70° of the signal behind the reference, caused by delays in the electronics.  This is constant throughout the measurement.

[Ringding · Accepted solution]

Sorted it.

Another rookies mistake!  I had forgotten to connect the 'Apply' input to initialise the PLL and the demodulator.