Thanks!
I realized that I need to find the appropriate values for sampling rate and min record length. The Extract Single Tone Information VI works fine. I can insert the division by the square root of 2 to get the RMS value — not a problem.
The Avraged DC-RMS VI is still not working, though now it is not needed.
I attached my awful VI file. It was made to check the possibility of measuring the current consumption, output signal amplitude and frequency of the device under test. Actually have to measure a couple of device parameters by changing the frequency, signal level from the generator, and the control voltage. It is necessary to make a new VI based on a finite state machine. But this is offtopic, sorry.