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Author Topic: Building a Fluxgate Magnetometer  (Read 21304 times)

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Offline dtrewren

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Re: Building a Fluxgate Magnetometer
« Reply #30 on: 16:43:26, 02 June, 2013 »
I know the feeling .... I have spent the last two hours fixing a jet washer which froze over the winter and then exploded within thirty seconds of use. High pressure water really wants to escape. Anyhow all working now ...phew

Very interested in your data. I want one but I think I have enough project work at the moment.
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Online tomhow

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Re: Building a Fluxgate Magnetometer
« Reply #31 on: 17:46:30, 02 June, 2013 »
Couple more shots :) You can just see the DHT22 sensor in the back behind the FGM-3h
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Offline swashy

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Re: Building a Fluxgate Magnetometer
« Reply #32 on: 21:14:53, 02 June, 2013 »
Intriguing!
Ade

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Offline psjshep

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Re: Building a Fluxgate Magnetometer
« Reply #33 on: 22:37:43, 02 June, 2013 »
so.... does this collect the grime from the radiator system so I don't have to power flush every 5 yrs?

Phil


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Online tomhow

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Re: Building a Fluxgate Magnetometer
« Reply #34 on: 15:02:57, 03 June, 2013 »
Phil's got his helpful hat on again! :)
Tak Sky 90, Atik 490, Homemade Mount, OAG, Lodestar

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Re: Building a Fluxgate Magnetometer
« Reply #35 on: 15:03:55, 03 June, 2013 »
Intriguing!

Right now I'm wondering if the readings I'm getting are real variations or it is the sun shining on the power supply/arduino crystal!
Tak Sky 90, Atik 490, Homemade Mount, OAG, Lodestar

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Offline Nomis Elfactem

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Re: Building a Fluxgate Magnetometer
« Reply #36 on: 15:31:34, 03 June, 2013 »
Phil's got his helpful hat on again! :)

I thought that too

Wow... you've moved on nicely Tom... there other thing to remember is there is a natural daily cycle that needs calibrating out... it has a specific name... will try and find the info I have on it but sure it was in one of those links I posted earlier.

S.
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Offline psjshep

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Re: Building a Fluxgate Magnetometer
« Reply #37 on: 20:07:16, 03 June, 2013 »
Phil's got his helpful hat on again! :)

I thought that too


 :butt:

It just reminded me of the magnet thing that was used when our Rads were flushed.... and with the plastic tubing an' all.....   :pirate:

Phil
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Re: Building a Fluxgate Magnetometer
« Reply #38 on: 22:16:15, 03 June, 2013 »
I could do with a radiator.... trying to work out how to get a regulated 5v power supply that is temperature stable to within 1mV over 0C to 30C....
Tak Sky 90, Atik 490, Homemade Mount, OAG, Lodestar

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Offline Hoohoo

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Re: Building a Fluxgate Magnetometer
« Reply #39 on: 04:14:15, 05 June, 2013 »
I could do with a radiator.... trying to work out how to get a regulated 5v power supply that is temperature stable to within 1mV over 0C to 30C....

Depending on the current needed, either use a voltage reference directly or use a voltage reference to set the bias of the regulator ;)
Quick google search revealed the TI burr brown ref02, 10ppm/C guaranteed. so 0.3mV at 30C temperature variation.
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Re: Building a Fluxgate Magnetometer
« Reply #40 on: 08:21:17, 05 June, 2013 »
Thanks Kim - the loadis about 20mA

I did find one of these monsters
http://uk.rs-online.com/web/p/voltage-references/7618282/

A 100mA reference! I am still a bit nervous at using it as a regulator - how does one set the bias of a regulator? I'm afraid I have a terrible blind spot on power supply design!!
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Offline Hoohoo

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Re: Building a Fluxgate Magnetometer
« Reply #41 on: 14:53:06, 05 June, 2013 »
At 20mA I would use something like the part you found (great find BTW!), less parts to go wrong and it is rated for it.

I am not sure exactly how to use the reference with a normal regulator, but using a adjustable regulator it should be possible. Probably easier to use a unity gain OP-AMP circuit instead.

To be honest I`m no expert in analog designs either, just dont practice it very much unfortunately :(
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Re: Building a Fluxgate Magnetometer
« Reply #42 on: 15:42:58, 05 June, 2013 »
I've got that part on order now :)

I'll cascade it after a 9v linear regulator so it ought to be fairly stable.

The FGM-3h is very sensitive to supply voltage. Around 3.5% / Volt.

Whilst the FGM is buried in the garden to keep it thermally stable, the rest of the electronics isn't - and your average linear regulator is something like +/- 10mV over typical diurnal/seasonal temperature changes... especially without central heating.

Given the full range on the FGM is something like 30uT , a supply variation of 10mV creates an error in the order of 10nT.

10nT might not seem like a lot, but the typical diurnal magnetic field changes are about 100nT.

Power supply noise is less of an issue... 20uV of noise is not going to be noticed.

Another aspect is timing. The crystal on the Arduino is also effected by temperature and voltage etc, so I'm looking at picking up my timing from either a temp compensated RTC or a PPS output from a GPS module.


Tak Sky 90, Atik 490, Homemade Mount, OAG, Lodestar

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Offline Hoohoo

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Re: Building a Fluxgate Magnetometer
« Reply #43 on: 16:31:55, 05 June, 2013 »
Cool, looking forward to see how it turns out.

It might have been mentioned earlier, have just skimmed the thread, but how do you do the initial calibration?
I like this project from an engineering point of view, so would be interested to know ;)

Not sure how critical the timing is, but GPS sounds good, it also has the advantage of giving exact UTC time in one of the messages, so precise time stamps is quite easy to do. Using a combination of the GPS and crystal the resolution should get into to the sub 1mS without trouble, use the PPS to calibrate he crystal timing which again is used to give the sub 1mS time.
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Re: Building a Fluxgate Magnetometer
« Reply #44 on: 16:58:10, 05 June, 2013 »
It might have been mentioned earlier, have just skimmed the thread, but how do you do the initial calibration?
I like this project from an engineering point of view, so would be interested to know ;)


You wrap a coil around it and run a small current through it to create a known magnetic field. I've not actually done that yet :)
Tak Sky 90, Atik 490, Homemade Mount, OAG, Lodestar

The Curdridge Observatory

 

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