Flux gate question

George Herold · 2013-02-08T16:58:25+00:00

Any fluxgate experts? I recall Jan posted some thing a while back. A colleague has made a flux gate by sticking to inductors side by side (with the axes in the same direction), but wired so the fields are in opposite directions. There?s then a pickup coil that is wrapped around the pair (all coils with a common axis). I?m trying to understand the ?scope trace. First off the inductors are Bourns 5800-392-RC, L= 3.9mH, R= 8 ohms Ioperate=0.1A, Isat=0.2amp The L/R ?frequency? is about 300Hz. I ?m driving them at 200 Hz and monitoring the drive voltage. So there is a bit of a phase shift between the displayed voltage and the current (which is what I care about.) I?ll show a current waveform below. I?ve got a max current of ~0.6A about 3x the 10% saturation current. Here?s a ?scope shot with B=0 So I interpret this trace as follows: The two inductors have different saturation currents one inductor saturates first, and the pickup coil then sees an increasing B field. As the second inductor saturates there is no longer any change in the B field. And I?m left with a spike. As the current decreases the same thing happens, but in reverse. And I get another spike with the opposite sign. My question is why do these two pulses have different widths/ amplitudes. The one for increasing current is always sharper and higher. (I tried another pair of inductors same type of behavior.) I wondered if it might be the opamp driving the inductors (OPA544)? I also measured the current (0.5 ohms in series) Here?s the signal with a sine wave There a bit of weirdness near the pulses. I also did it with a triangle wave drive here, For completeness here are pictures with a B field applied in one direction and then reversed Is there a ?physics? reason for the asymmetry? or just electronics? (I was thinking I could try an RC Zobel network in parallel with the coil?) Thanks George H.

Feb 08, 2013 142 Replies

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Joerg 13 years ago

[...]

Like where you open the box and something hisses at you from the inside? :-)

[...]

Regards, Joerg http://www.analogconsultants.com/

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Charlie E. 13 years ago

Actually, it is when you reach in to plug in an outdoor plug, and a 2" black widow crawls out... ;-)

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Joerg 13 years ago

Out here we have the brown recluse. Those bites can be especially nasty.

Regards, Joerg http://www.analogconsultants.com/

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