How to measure high current pulses without the noise?

[fritz]

Hi,


I would use similar setup used for EMV measurements.
1) large grounded sheet metal plane as reference plane
2) strip grounded oscilloscope on the reference plane
3) isolated differential probe to convert differential signal to unbalanced scope input
http://www.tek.com/oscilloscope-probes-and-accessories/differential-probe-high-voltage
4) A shunt made out of konstantan or similar sheet metal with twisted pair from the ends coupling to the differential probe
5) ground the shunt (only grounding point of setup) in the middle as symmetric as possible
6) Using capacitors with symmetric parasitic capacity to ambient potential (don´t use metal cap types - because one end has more capacity to ground than other)
7) Try to arrange your setup in a way that impedances regarding ground (reference plane)on both shunt ends  are pretty the same (if you want to measure Mhz - this impedance should work in this range also)


-> Try to get as minimal common mode disturbancies as possible.


Thats straight forward - and should be no problem with few 100kA
For shunt construction - you should think about total energy consumed, thermal capacity of shunt (....)


rgds.

[MarkE]

Hi,


I would use similar setup used for EMV measurements.
1) large grounded sheet metal plane as reference plane
2) strip grounded oscilloscope on the reference plane
3) isolated differential probe to convert differential signal to unbalanced scope input
http://www.tek.com/oscilloscope-probes-and-accessories/differential-probe-high-voltage
4) A shunt made out of konstantan or similar sheet metal with twisted pair from the ends coupling to the differential probe
5) ground the shunt (only grounding point of setup) in the middle as symmetric as possible
6) Using capacitors with symmetric parasitic capacity to ambient potential (don´t use metal cap types - because one end has more capacity to ground than other)
7) Try to arrange your setup in a way that impedances regarding ground (reference plane)on both shunt ends  are pretty the same (if you want to measure Mhz - this impedance should work in this range also)


-> Try to get as minimal common mode disturbancies as possible.


Thats straight forward - and should be no problem with few 100kA
For shunt construction - you should think about total energy consumed, thermal capacity of shunt (....)


rgds.

The common mode rejection of those probes is down to ~30dB at a couple of MHz and further degrades to their bandwidth limit.  Armoring the power and probe cables with clamp on ferrites is often the only effective way to keep common mode noise from getting into the oscilloscope vertical amplifiers without putting the EUT in a screen room.  The big reference plate under the scope that you suggest is sort of a DIY screen room that is not fully enclosed.