The signal that I get with the oscilloscope comes from Lock-in CH1 OUTPUT. It is much higher than the signal recorded by the vi (the AC signal in entry 252, for example).

I read the sr830 lock-in  manual and I found that the CH1 OUTPUT voltage is proportional to the AC signal according to the following formula:

Output = (signal/sensitivity - offset) x Expand x 10 V

The Expand factor is 1, the sensitivity is 1mV, as we can see in the picture of the front panel.

So in the case of signal = 15uV , for example, I get Output = 150mV, a factor 10^4 higher