Author Topic: Rogowski current probe  (Read 322 times)

Offline flyglas

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Rogowski current probe
« on: September 14, 2020, 08:35:10 PM »
Hello,
does somebody have access to a (perhaps broken one) rogowski current probe for use with an oscilloscope?
I cannot find any pictures from the inside of such a probe (integrator part of the probe) anywhere in the internet.
I would be very happy if someone can open a probe and take some pictures.
« Last Edit: September 14, 2020, 08:36:59 PM by flyglas »

Offline Hydron

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Re: Rogowski current probe
« Reply #1 on: September 14, 2020, 09:02:19 PM »
I second this, but I'm also interested in the construction of commercial probes, especially the skinny high-frequency ones (you can get them thin enough to thread through a TO-247 leg!

It's one thing winding a skinny coil, another to do it such that it doesn't pick up all sorts of garbage from E-fields etc yet still is flexible and high-bandwidth (the obvious ideas like a shield tend to work against these).

Offline johnf

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Re: Rogowski current probe
« Reply #2 on: September 14, 2020, 09:03:43 PM »

Offline davekni

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Re: Rogowski current probe
« Reply #3 on: September 14, 2020, 09:31:47 PM »
Sometimes a very cheap simple solution works fine, especially if there's a way to calibrate.  I once needed to probe output current of a large H-Bridge.  Wrapped 10 turns around the end of a felt-tip marker and wedged that between the two wires of the output cable.  Coil ends connected to a scope.  Captured waveforms and integrated with software.  Used a known 800A waveform for calibration.  It was then very useful to capture high-frequency details of the current waveforms that weren't visible previously.

Also tried a similar test on my DRSSTC H-Bridge output.  This time I added a non-shorted turn of copper foil around the coil for shielding.  Worked fine, but I didn't keep it.  My CT already has a scope tap, and digital integration isn't convenient for real-time viewing.
David Knierim

Offline johnf

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Re: Rogowski current probe
« Reply #4 on: September 14, 2020, 09:47:08 PM »
Hydron
I built a tiny current transformer to go over the source lead of a TO220 fet (actually a 5 pin PowerIintegrations SMPS device) to actually see what was going on
I had already tried a 0.01 ohm resister to scope over but introducing the resistor caused other effects and masked my problem.
I used the core out of a ISDN modem that had common mode chokes on the data ports i pulled the core out and wound with 38awg wire 200 turns on it and high voltage varnished it up along with a 1.0 ohm burden resistor. Net effect was this causes 0.000025 ohms of impedance on the source lead which in my case was low enough to go back to Power Integrations for them to ponder over. I ended up making a second transformer and sending it to them for their use in their lab

Offline johnf

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Re: Rogowski current probe
« Reply #5 on: September 14, 2020, 10:55:54 PM »
Kludgesmith asked me for some pics of the common mode choke i stole the cores out of so here they are



Offline johnf

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Re: Rogowski current probe
« Reply #6 on: September 14, 2020, 10:57:36 PM »
another pic

Offline johnf

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Offline flyglas

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« Last Edit: September 15, 2020, 07:35:09 PM by flyglas »

Offline Hydron

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Re: Rogowski current probe
« Reply #9 on: September 16, 2020, 09:38:14 PM »
Sometimes a very cheap simple solution works fine, especially if there's a way to calibrate.  I once needed to probe output current of a large H-Bridge.  Wrapped 10 turns around the end of a felt-tip marker and wedged that between the two wires of the output cable.  Coil ends connected to a scope.  Captured waveforms and integrated with software.  Used a known 800A waveform for calibration.  It was then very useful to capture high-frequency details of the current waveforms that weren't visible previously.

Also tried a similar test on my DRSSTC H-Bridge output.  This time I added a non-shorted turn of copper foil around the coil for shielding.  Worked fine, but I didn't keep it.  My CT already has a scope tap, and digital integration isn't convenient for real-time viewing.
Hmm, will need to give the similar simple setup I tried and wasn't happy with another go given I have a better scope these days.

As for small CTs, I spied these guys in a power supply teardown once:

(from https://www.tomshardware.com/uk/reviews/corsair-ax1600i-psu,5406-3.html)
Can also be seen here: http://www.jonnyguru.com/wp-reviews/CorsairAX1600i/DSC_2384.jpg

I never had any luck finding a way to order these unfortunately - they look super handy! Any lead on them would be most welcomed.

Offline flyglas

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Re: Rogowski current probe
« Reply #10 on: September 17, 2020, 07:43:00 PM »
@Hydron: I have asked the manufacturer of the GaN switches in the Corsair PSU about the tiny current sensor via mail. Perhaps they will answer my question.

Yesterday i bought a rogowski coil PEM CWT from ebay. Perhaps the unit will satisfy my thirst for knowledge.

Offline Hydron

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Re: Rogowski current probe
« Reply #11 on: September 17, 2020, 10:26:57 PM »
May I ask how much you paid? I haven't really looked seriously, but what I did see was silly money (i.e. business purchase $$$, not hobby). I am certainly interested in what you find!

Offline flyglas

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Re: Rogowski current probe
« Reply #12 on: September 18, 2020, 02:49:05 PM »
Hi Hydron,

I paid 174 EUR including shipping from Italy to Germany. That is a fairly good price.
--> https://www.ebay.de/itm/PEM-CWT-6R-Rogowski-Current-Waveform-Transducer/254344545232


Offline Hydron

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Re: Rogowski current probe
« Reply #13 on: September 19, 2020, 11:34:01 PM »
Thanks,

I did see this internal picture, may be of interest as you wait for your unit:
https://gmw.com/wp-content/uploads/2019/03/CWT_Fuse_Replace_Instructions_GMW.pdf

Is not showing the cable entry from the coil (goes in the hole at the top), but there isn't a whole lot going on in there! Would be good to see and compare to the inside of the one you have coming.

I am definitely interested in how the coil is made, but unfortunately this is difficult to do non-destructively unless you have an x-ray machine handy.
From the info I can gather from PEM publications etc, some of their probes look to be shielded, some not, so there may be quite a range of performance in the presence of high dV/dt.

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Re: Rogowski current probe
« Reply #13 on: September 19, 2020, 11:34:01 PM »

 


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