Phase change in lock-in amplifier

[Mikech]

I just started to use a lock-in amplifier, and I am trying to following the procedures by adjusting zero phase. But my input phase changes with time and sensitivity, and I couldn't lock in onto it. The question is, is this normal that phase changes all the time during the experiment or if there is something wrong with it?

here is some numbers

pre-amplifier sensitivity was set to 1e-5,1e-6,1e-7)
With lock-in amplifier sensitivity (1 mV), phase changes between ~ +170 through -170 degrees
With lock-in amplifier sensitivity (5 mV), phase changes between ~ +90 through -90 degress
With lock-in amplifier sensitivity (10 mV), phase changes between ~ +40 through -40 degrees


Thanks

 

[NascentOxygen]

Hi, Mikech, and welcome to Physics Forums.

The phase difference varies with the gain of the error amplifier (sensitivity). That's how the PLL works. I'm not sure what you mean by time, but I'd look closely at your measuring techniques, before concluding that the arrangement is not working as advertised.

Obviously, the signal generator you are coupling to the circuit should not be affected by the circuit. You should use the input as reference (usually).