Rogowski current probe

[klugesmith]

Agreed, 10 mV is not weak as electronic signals go.
What's the noise level at microphone input to a PC audio "card"?  Digitized voltage signal could be low pass filtered, averaged, and (lest we forget) integrated offline.

Just remembered the commercial model 916 fluxmeter box.  It does voltage integration, is plenty fast for 60 Hz, and has offset voltage low enough for "DC" measurement.  Invites Rogowski coil tests on DC buses whose current can be switched on and off.
https://highvoltageforum.net/index.php?topic=819.msg5555#msg5555

This chat has served as reminder that fancy winding (34 AWG magnet wire, wound beautifully, maybe with mechanically controlled pitch) is probably unnecessary for stated objective, DIY flexible coil for a single application.
Would be a briefly engaging squirrel-chase.

[flyglas]

Here is a picture of the windings of the Ultra Mini probe: Page 19: https://gmw.com/wp-content/uploads/2019/01/APEC-March-2015.pdf

[klugesmith]

Thanks; the picture of "Old CWTUM" started a very satisfying squirrel chase.


Picture shows 50 turns in 6.1 mm, for winding density of 8200 turns/m (208 turns/inch). Estimated coil diameter is 1.15 mm outside and 0.91 mm inside. The larger red rectangle is 1.7 mm high, matching the Ultra Mini jacket OD.
Using coil mid-diameter, computed sensitivity is 8.55 nH. 
Anybody seen that parameter given in literature from PEM, or other commercial RC maker?

My test of closely-wound AWG34 magnet wire got 5900 turns/m (150 turns/inch).  Can probably get 2100 turns/m with plain old wire-wrap wire.  In a 5.5 mm coil that would give us 63 nH.  On 200 A at 60 Hz, 4.7 mV.

[flyglas]

Thanks for image processing and the squirrel chase. I had the same idea but no time today.

I also have done the math (with your values) and calculated the same mutual induction as you.
The mutual induction value is plausible.

With a integrator time constant of 1.7 µs (R = 1700 Ohm and C = 1.0 nF) we have a sensitivity of around 5 mV/A.

[flyglas]

I have a short update.

A few days ago I received PCBs for a rogowski coil integrator.
Additionaly I wound a small coil onto the insulator PTFE of an RG178 coaxial cable.
The insulator has an diameter of 0.86mm and the used wire is 0.1mm. The windings are wound without space between the windings.
As a protective layer a heat shrink is on top of the wire. The total diameter of the coil is only 1,75 mm.

At the moment I only tuned the low frequency range (active integrator with opamp).
A test at 50 Hz and around 6 A peak shows the same respones as my professional coil.
Both coils are designed to have 5 mV/A output signal.

The next step is to tune the high frequency range (passive integrator).
For this task I designed a pulse generator (16 µs pulse with 150 A peak and flat top, rise and fall time around 800ns).
I found the calibration procedure/waveform in an official calibration document.

[klugesmith]

Very nice work. 

It shows that 6 amps at 50 Hz gives a useful signal, even with the tiny area of minor loops in the coils.
Have you looked at the sensitivity to test currents routed outside the R.C. loop, or threading the loop backwards?

Will we get to see any pictures of your helical winding operation?

What is the low frequency corner of the active integrator circuit?

[flyglas]

Have you looked at the sensitivity to test currents routed outside the R.C. loop, or threading the loop backwards?

I have build a current pulse generator (150A, ~750ns rise and fall-time, 20µs pulse width) for adjustments to the high frequency passive integrator.
With this puls generator and two turns of wire, I have tested the influnece of nearby current pulses.
Depending of the position the influnece is well noticable (see pictures influence_diy_1...3).
With the commerical unit the influence was also noticable, but almost only at the t-piece (see picture influence_prof_1).
The resumee is: Keep away with currents from the t-piece.

Will we get to see any pictures of your helical winding operation?

This was no big deal. I removed the inner conductor of the PFTE insulator and replaced it with the 0.1 mm enameled wire.
At the open end I applied a tiny ammount of epoxy glue. After curing the insulator was twisted between to fingers to wind the wire around the insulator.
Everything is held together with the heat shrink.

What is the low frequency corner of the active integrator circuit?

I did not tested it yet. Simulation shows good results down to 1 Hz.