measuring floating ground with digitizer

[Randy36]

I need to measure an AC source at 350kHz and it is on a floating ground. 

How can I do this with my high-speed digitizer (basically just an O-Scope). 

I need to use both channels so a differential reading isn't an option. 

Are there pre-made isolation circuits I can buy that can handle the 350kHz without causing major distortion?  

[johnsold]

How much isolation voltage do you need?

Lynn

[Randy36]

What exactly do you mean by that?

The source is about 200-400 Vpeak while under load.

The plan is to drop that voltage to measurable range of about 5-10 Vpeak using a voltage divider.

So we'll be physically measuring a sin waveform @ 350 kHz and 5-10 Vpeak.

Would that be the Isolation Voltage?

[johnsold]

The isolation voltage is the difference between the reference potential of the floating system and the reference potential (probably ground) of the measurement system.  Another way to describe it is the voltage which might exist between the floating "ground" of the 350 kHz system and the "ground" of your measurement system.  When talking about isolated systems is is better to avoid the use of the term "ground" to avoid confusion.

There is always some coupling between the two systems. There will be capacitance and inductance. There may be some leakage resistance. Power lines create ubiquitous electric and magnetic fields to excite the coupling between the systems. Of course voltages and currents within the two systems can also couple. Usually the coupling can only be estimated or guessed, but often an upper limit on the potential difference between the two systems can be determined.  That upper limit is the lower limit for the isolation voltage rating required.

Lynn

[Henrik_Volkers]

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@johnsold wrote:

The isolation voltage is the difference between the reference potential of the floating system and the reference potential (probably ground) of the measurement system.  Another way to describe it is the voltage which might exist between the floating "ground" of the 350 kHz system and the "ground" of your measurement system.  When talking about isolated systems is is better to avoid the use of the term "ground" to avoid confusion.

There is always some coupling between the two systems. There will be capacitance and inductance. There may be some leakage resistance. Power lines create ubiquitous electric and magnetic fields to excite the coupling between the systems. Of course voltages and currents within the two systems can also couple. Usually the coupling can only be estimated or guessed, but often an upper limit on the potential difference between the two systems can be determined.  That upper limit is the lower limit for the isolation voltage rating required.

Lynn

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“ground” is a convenient fantasy!!

Easy way

http://www.tek.com/datasheet/differential-probe-high-voltage-differential-probes-datasheet

[johnsold]

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“ground” is a convenient fantasy!!

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Well said!

Lynn