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Flux gate question

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

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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

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There a bit of weirdness near the pulses.

I also did it with a triangle wave drive here,

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For completeness here are pictures with a B field applied in one direction

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and then reversed
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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.

Reply to
George Herold
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The chip I designed last year for the heavy truck clutch position sensor ;-) used two inductors aligned in the same direction but electrically connected in series opposing.

End-to-end was driven by a square wave, and the mid-point connection voltage was synchronously rectified and observed for second harmonic content, which content was proportional to field.

There was no pick-up coil.

Horrible loading time for your images :-( ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

Interesting... I'll have to think about it. I'm working on the synchronous 2f detection.

Our 'baby' lockin has no 2f function. I'm thinking of a bridge rectifier and a little transformer.

I m

Does anyone else have this problem? I'd be happy to start using some other image hosting site. I liked this one 'cause it's easy for me. No registration or other mumbo jumbo.. just upload an image and copy the URL.

George H.

    ...Jim Thompson
   |    mens     |
  |     et      |
 |
      |

ide quoted text -

Reply to
George Herold

[...]

Nope. Blazingly fast here, loads whambam style as if they were on my harddrive.

Here Jim is always razzing me about my computation machine and now _his_ machine is behaving like a slow-poke, tsk, tsk, tsk ... :-)

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Nope. It's only bayimg.com that's butt slow, with strange behavior, first image selected loads fast, second choice spins the indicator, sometimes timing out before loading.

Is bayimg.com in Californica? ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

About a 2-3-second load time for me. Ping is 125-130msec.

Flickr is about a 35msec ping, less than 1.5 seconds to load.

How long does it take from your hard drive? ;-)

Reply to
Spehro Pefhany

Must be something wrong on your side. Or at your ISP but that's not very likely.

No idea. Normally doesn't matter because you wouldn't even feel 200msec latency if the server was at the South Pole, provided that the data streams fast enough. I get the same speedy reaction from image servers in Europe, when participating in NGs over there. Well, except those that are over-fluffified, script-laden or when my firewall stomps on the brakes because of nasty stuff in the data.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Ping give me 186-209ms.

Looks to me like the site blocks repetitive seeks... first image, doesn't matter which, is fast loading, close that window, click another image... wheel spin. Strange! ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

Way under a second load time here. Maybe the electrons are freezing a bit on the way to Canada. Ping is 191msec, so must be electrically farther away from me.

Flickr is 67msec ping.

No idea but first I have to find it in the directories and that takes time :-)

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Nah, ain't happening here. As I said, something must be wrong with the computation gear on your side ... :-)

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Pickups aren't heavy trucks!

Reply to
Michael A. Terrell

I can't find any records for that domain name, and it wasn't found on a name server. The site FAQ says it is parte of Pirate Bay, a Torrent site. That's probaly why I can't find any info on the location.

Reply to
Michael A. Terrell

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Enough chit chat about bayimg. :^) Does an inductor behave differently going into saturation versus coming out of it? Maybe I could just wind a pickup coil around one inductor and see how it behaves.... I stuck an RC zobel across the inductors R=16 ohms C = 20uF (C = L/R^2) (OK should have been ~30uF) This did absolutely nothing to the pickup signal.

I guess the difference doesn't really affect the signal, I'd just like to understand it.

George H.

Reply to
George Herold

When the coils go into saturation, the voltage across them is quite high and so is dI/dt. When they come out of saturation, the voltage is much closer near zero, and dI/dt is consequently much smaller. At a guess, I'd think that the symmetry should be better at 1kHz. Of course, you'd need to increase the drive voltage by five times too.

Jeroen Belleman

Reply to
Jeroen

Snicker all you want. I have one "problem" to your hundreds. And I don't have ANY crashes. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

Well?

(1) There's hysteresis (2) An inductor in saturation has doesn't store as much energy (3) And it probably is frequency-dependent ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

p

Oh, you mean because of the inductance! (I've been trying to draw B/H curves with different curvature going back and forth, but no hysterisis... didn't work to well)

At low frequency (~20Hz) they do become more similar.

  • At a guess,
  • I'd think that the symmetry should be better at 1kHz. Of course, you'd
  • need to increase the drive voltage by five times too.

Hey there's a new 140V opamp... but not much drive current.

Thanks Jeroen

Reply to
George Herold

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Thanks Jim, I don't think you need hysteresis to explain it. Jereon nailed it for me (I think.) It's just the inductance... going into saturation it's pushing me along, and coming out it's sorta holding me back... That snaps up the one side and stretches out the other. (excuse my anthropomorphizing)

George H.

    ...Jim Thompson
   |    mens     |
  |     et      |
 |
      |

ide quoted text -

Reply to
George Herold

I had only three programs that crash. They got voted off the island and replaced with similar software of adequate quality. Problem solved. Now there is only one (Skype) which I have to keep in order to communicate with one engineer. No other crashes whatsoever. It's simple: There is software of good quality and then there is software of lesser quality.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

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I was talking with someone who said the difference between German and US companies, is that US companies will ship stuff with software that sometimes doesn't work right.

George H.

Reply to
George Herold

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