Maximum existing external DC voltage allowed during impedance measurements

[toddkrein]

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?

[attila]

Hi @toddkrein

I don't know exactly your setup but I've used the AD2+IA to measure impedance of powered device. Either by using floating power supply for the device or USB isolator for AD2.
The scope inputs are have two gain/range steps 5/50V. At low range the resolution is better 5Vpk2pk, +/-8V input with +/-5.5V offset.
The AWG outputs should not be driven/shorted to external rail. When the AD2 is on these are protected up to +/-5V

[toddkrein]

15 hours ago, attila said:

Hi @toddkrein

I don't know exactly your setup but I've used the AD2+IA to measure impedance of powered device. Either by using floating power supply for the device or USB isolator for AD2.
The scope inputs are have two gain/range steps 5/50V. At low range the resolution is better 5Vpk2pk, +/-8V input with +/-5.5V offset.
The AWG outputs should not be driven/shorted to external rail. When the AD2 is on these are protected up to +/-5V

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...

[attila]

Hi @toddkrein

I think you can analyze the above circuit without powering it. With supply on Line it will likely damage the device/AWG !