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Rogowski coil construction

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aonomus

Thu Jan 29 2009, 02:12AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

So I've constructed the coil and given it a whirl using my coilgun and it seems to work ok. I don't have a integrator for it, it is only the rogowski coil itself plugged into a scope. Some construction photos:

I used a luer lock fittings (from syringes and fluid handling stuff) for the connector

A closeup of the coil.

I used 20ft of RG6 with a twist-on BNC connector (no crimper), 30AWG magnet wire for the coil itself.

For my first test I used my biggest induction motor fan on 120VAC and got this:

Test setup

Sinewave: 120VAC
Choppy wave: Current

My second test was with my coilgun with different projectiles and voltages, and worked out pretty well. I captured the waveforms using my laptop's soundcard as a cheap DSO, however I maxed out the card and the waveforms got clipped at higher powers.

Edit: Now all that remains is to both calibrate the coil, and also build the integrator

Edit 2:
Videos of the 300V and 430V tests, kinda boring but if you are interested:

likewhat

Thu Jan 29 2009, 02:31AM

Account deactivated by user request on 6/11/2009.
Registered Member #1071 Joined: Fri Oct 19 2007, 02:13AM
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Posts: 44

interesting results. A few questions/comments.

How do you terminate the coil. It is built in a 50 ohm cable right? are you terminating it into a 50 ohm connection, if not it will have weird reflections and you will see them on your scope.

Unless you buy something that comes with a calibration and you are using it within the design parameters you pretty much have to calibrate it for the frequency you are using it on. So if you need to measure something that puts out 1000 amps with 1 us rise time you should calibrate it on a 1 us rise time pulse that has an amperage output you can reliably measure.

If you are maxing out your card you should get some attenuators for it. I dont know how much they cost cause we just have piles of them in the lab I work at but they are super useful, that way you dont have to build a different probe for every different machine you measure current on.

aonomus

Thu Jan 29 2009, 02:46AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

Well in

you can see its a 75 ohm cable, the coil itself has 2 connections, one end to shield, one end to center conductor. I sadly couldn't find any 50ohm cable, perhaps one day I will build a new one on a 50ohm cable.

What would the reflection look like on a scope, I've tried low frequency, high frequency, and pulse and I haven't gotten any visible reflections, although on some HF measurements I got unstable triggering on my scope, however I suspect that is due to the HF source being the charger circuit on my coilgun, and that it naturally fluctuates...

I'll have to read up on calibrating it anyway.

rp181

Thu Jan 29 2009, 04:47AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

I was winding one, and i was wondering, what if the loop is too big? can it be too big (within limits)?

101111

Thu Jan 29 2009, 12:03PM

Registered Member #575 Joined: Sun Mar 11 2007, 04:00AM
Location: Norway
Posts: 263

About impedance it connectors and cables on this topic:
I can hardly see that it matters, as far as I know this is only relevant when it come to high frequencies.
I think as long as the cable are shielded it should be O.K, but I might be wrong..

rp181

Thu Jan 29 2009, 11:34PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Hey all,
I just finished winding a coil. Its wound with 30 AWG. I was talking to aonomus about just putting the coil next together, instead of a Tee. Would this method work? Here are some pics:

BTW, in the first pic, the ends are closer together then they appear. one end was bent up a little.

EDIT: I just tried it with a 3900uf capacitor charged to 160v. The wave is nice and clean, and it is also cut off. It wasn't a coilgun, it was hard shorted with a SCR. Im going to try mains now, ile post pics when im done with that.

aonomus

Tue Feb 03 2009, 10:59PM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

So I've done up a schematic, slightly modified from Dalus's link (post #4 I believe), its a bit of a monstrosity, but its single sided and uses a bunch of jumpers. I have modified the board to use fewer since then, but its still pretty bad....

rp181

Wed Feb 04 2009, 02:19AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

nice, where do you plan on getting the TL071P's?

aonomus

Wed Feb 04 2009, 03:28AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

Well TDU's active integrator is very similar to this, including the opamp (TL071), however discussions with Steve Conner said that I'd need opamps 10-100x faster than the time constant of the pulse (assuming a 1-10ms pulse, that means the TL071 is too slow). Since TDU's worked with TL071's, I will try the design with this first, and if they are too slow and I get residual voltage offset, I'll switch to a pin-equivalent faster opamp.

rp181

Wed Feb 04 2009, 04:33AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

What is the intended application? I was reading some paper's, and passive will suffice for some. Since mine will be a permanent installation, passive will work fine.

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