Measuring voltage between two points...wirelessly?

Question

I want to measure voltage between points A and B. Let's assume that there's some obstruction/difficulty in simply attaching cables between those points. Is it possible to measure the voltage wirelessly somehow?

I had an idea of a device that measures voltage at some point with reference to an on-board stable potential S. Let's say two such devices are attached to points A and B:
Device 1 measures voltage between A and S
Device 2 measures voltage between B and S
Measurements are then transmitted wirelessly to a server. Is it possible to "substitute for S" and recover voltage between A and B?

Thank you in advance for your answers :-)

Answer 1

There's no such thing as an "on-board stable potential" with reference to the outside world. All voltages are relative - a voltage is a potential difference - so in order to measure the voltage between two points, you either need to compare them directly, or you need a common reference potential to compare each to.

In a small area you might use neutral or an earth ground as your common potential, but these can vary over larger areas.

The obvious question is, if you don't have a potential you can use as a reference for both measurements, then how will the resulting measurement be meaningful or useful at all?

Answer 2

Well, to measure the current wirelessly, one can utilize a clamp ampermeter. Although, details are not provided, I suppose this is not what you are looking for; as you can come to the voltage if you know the resistance in between and current is not divided on it's way between the points.