The setup:
-A 1 Vrms 1 KHz sine wave, transformer balanced signal with 600 Ohm impedance, completely floating. (The source is powered from a 9V battery.)
-ESD mat on the table and both the signal source and the Fluke are on the ESD mat.
I was expecting to see 1 Vrms at the output but instead I got 0.56 Vrms. Expecting the Fluke to be broken I take the same measurement with an other Fluke. This one seems to show 0.8 Vrms. But after changing the polarity, this one also measures 0.56 Vrms instead of 1 Vrms.
Confused I measure the signal with an oscilloscope and the signal is indeed 1 KHz, 1 Vrms as should be.
I then put the Fluke which was still connected to the signal source aside, of the ESD mat. But to my surprise, the reading is now 1 Vrms.
The Fluke manual states nothing about the source impedance for AC signals. What's wrong here?