Calculate the input impedance of a passive AC voltage sensor
Attach an appropriate  load to the device and an appropriate input voltage to the device. Measure the AC voltage directly across the input terminals of the device. Call this E 1 . Measure the voltage across one of the input resistors, R. Call this E 2.

Now calculate the current through the circuit as:

I1 =E 2/R

Now calculate the input impedance as:

|Z|=E 1 /I1