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From: Falk Willberg on 14 Feb 2010 17:42
Am 14.02.2010 23:16, schrieb Jan Panteltje:
....

> I think this way:
> I get a delta f of 82000 Hz for a 0-1.2 Tesla at the front of the inductor.
> So about 68 Hz per milli Tesla.

A standard AMR magnetometer (Honeywell makes some) for less than 5� has
a resolution of 7 mGauss. (Turn it on... Ok, the 48�T of Earth's
magnetic field give me a reading of ~560) Some of them (HMC5843, YAS529)
have a convenient digital interface.

Falk
--
My english may be bad, but you should hear me shout "Achtung, Fritz, die
Autobahn".
From: Jan Panteltje on 14 Feb 2010 17:59
On a sunny day (Sun, 14 Feb 2010 23:42:38 +0100) it happened Falk Willberg
<Faweglassenlk(a)falk-willberg.de> wrote in
<hl9u8v$jmm$1(a)news2.open-news-network.org>:

>Am 14.02.2010 23:16, schrieb Jan Panteltje:
>...
>
>> I think this way:
>> I get a delta f of 82000 Hz for a 0-1.2 Tesla at the front of the inductor.
>> So about 68 Hz per milli Tesla.
>
>A standard AMR magnetometer (Honeywell makes some) for less than 5� has
>a resolution of 7 mGauss. (Turn it on... Ok, the 48�T of Earth's
>magnetic field give me a reading of ~560) Some of them (HMC5843, YAS529)
>have a convenient digital interface.
>
>Falk

Yes, possible, but this did not cost me anything as I have all the stuff...
But also the resolution depends on how the micro measures frequency.
If it measures time between zero crossing then you can measure very long periods...
Not that I want to do that, if I wanted to measure something as weak as the
direction of the earth magnetic field I could put a webcam on a compass :-)
I think the parts cost of this is still below 5 $, including the PIC frequency meter with RS232 output.
The 9 pol RS232 connector is more expensive, especially the screened cap :-)
From: Fred Bartoli on 14 Feb 2010 18:20
Jan Panteltje a �crit :
> On a sunny day (Sun, 14 Feb 2010 23:52:27 +0100) it happened Frank Buss
> <fb(a)frank-buss.de> wrote in <ue1lj9t2hqtf.e0mkaq52n6mq$.dlg(a)40tude.net>:
>
>> Jan Panteltje wrote:
>>
>>>
>>> For a project I am doing I need to measure high currents.
>>> I was thinking if I could somehow use core saturation to measure the magnetic field,
>>> and thus the current in a close conductor.
>>> The idea is to have two the same LC oscillators, and then magnetise the ferrite core of one of those,
>>> and mix the output, use the difference frequency in a micro, a PIC to be precise.
>>> Either that, and the system should no use a shunt, or use one of those Hall sensors.
>>> So I did set up a quick experiment, using the small strong magnet I have as a simulated magnetic field from
>>> some turn of high current wire.
>> I think measuring the magnetic field with a coil is not a new idea:
>>
>> http://lark.tu-sofia.bg/~ntt/pesu/readings/Compass.pdf
>
> No of course not, but in the end I want to measure a high DC current.
>

Get hold of the HP428A/B DC mAmeter manual and read it.

It is essentially the same flux gate, with the measured current going
through the core along with a current compensating winding, all that
brought to zero net flux through a feedback loop.
That one is, by design, free of all the ferrite non linearities and
temperature dependencies.


> Interesting paper, thank you.
>
>
>> There is even a company who sells compass sensors, made with coils and an
>> ASIC for signal conditioning, but I've forgot the name. The resolution is
>> in the range of micro tesla.
>
> Yes, that circuit in tha tpdf could use a PIC :-)
>


--
Thanks,
Fred.
From: Phil Hobbs on 15 Feb 2010 11:51
On 2/14/2010 5:59 PM, Jan Panteltje wrote:
> On a sunny day (Sun, 14 Feb 2010 23:42:38 +0100) it happened Falk Willberg
> <Faweglassenlk(a)falk-willberg.de> wrote in
> <hl9u8v$jmm$1(a)news2.open-news-network.org>:
>
>> Am 14.02.2010 23:16, schrieb Jan Panteltje:
>> ...
>>
>>> I think this way:
>>> I get a delta f of 82000 Hz for a 0-1.2 Tesla at the front of the inductor.
>>> So about 68 Hz per milli Tesla.
>>
>> A standard AMR magnetometer (Honeywell makes some) for less than 5� has
>> a resolution of 7 mGauss. (Turn it on... Ok, the 48�T of Earth's
>> magnetic field give me a reading of ~560) Some of them (HMC5843, YAS529)
>> have a convenient digital interface.
>>
>> Falk
>
> Yes, possible, but this did not cost me anything as I have all the stuff...
> But also the resolution depends on how the micro measures frequency.
> If it measures time between zero crossing then you can measure very long periods...
> Not that I want to do that, if I wanted to measure something as weak as the
> direction of the earth magnetic field I could put a webcam on a compass :-)
> I think the parts cost of this is still below 5 $, including the PIC frequency meter with RS232 output.
> The 9 pol RS232 connector is more expensive, especially the screened cap :-)

A flux gate is more accurate, and doesn't take a lot more work.
Flipping it around helps get rid of remanence.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
From: Falk Willberg on 16 Feb 2010 04:27
Am 15.02.2010 22:32, schrieb Jim Thompson:
....
> My flux gate controller chip, posted about earlier, did "flip" and
> auto-zero between EVERY measurement phase.

I couldn't find any newer flux gate magnetometer from Honeywell but many
AMR type chips. Those had the Set/Reset-Coils.

1A(a)3V sounds like a lot of power, but the duration of the pulses is ~1�s
and you need two pulses vor every measurment.

I used a simple push-pull and a 1�F capacitor before Honeywell
introduced the HMC5843 with integrated analog circuitry.

Falk
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