toddkrein

Attila, thanks for the feedback. My problem is that the phone is powered by the same two pins that would be connected to the analyzer, not by a separate power input. While the signal above is over-simplified, the "signal in" section is powered by the +7V difference between the two line inputs. I suppose if I used a floating supply it might work...

I need to measure the impedance of a telephone monitoring device, but this device pulls current from the active phone line to power itself. Thus to turn on the device I need to apply an external 7Vdc to the same wires that are connected to the impedance analyzer board. Will this damage the AD2?