Rainer's quest to build a magnetometer

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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

Carbon60 wrote: Sun Mar 20, 2022 7:25 am
rsfoto wrote: Sat Mar 19, 2022 8:30 pm
What do you see in the screen at the micro volt level ?
Hi Stuart,

Below a graph of about 40 minutes of time taken with onyl one coil. Just wound the second in opposite direction and graphing for an hour at the moment. That is the maximum time my multimeter allows to graph.

If you check that the variation is between 1.2 µV to about 1.8 µV or 0.0000012 to 0.0000018 V ¿ correct ?


Image
It shows how electrically noisy it is in your workshop, which is to be expected. If you set up your sensor in the location where you you intend to install your magnetometer you’ll be able to determine how noisy it is there. If it is much quieter on your scope, which would have to be set some metres away, then you might be in with a chance. The challenge with your system is that the connecting wire between the sensor and your detector will also act as a ‘sensor’ and will suffer from interference if not properly shielded.
FGM sensors work by generating an output frequency rather than fluctuating voltage. It’s this variable frequency that I measure. Voltage outputs are subject to extraneous effects created between the sensor and the detector, messing up your geomagnetic data. You could try to configure yours to drive a voltage controlled frequency generator close to the sensor, but then this itself will create its own magnetic field which will affect the sensor….. tricky.

Stu.


Hi Stuart,
It’s this variable frequency that I measure.
OH, so this a FM matter and not AM matter . Need to read more about this ... All what I have read so far talks about voltage differences ...

Thanks. we are talking here about microV not even milliV according to what I see on the screen. The lower value even has nanoV ...

OK, right now I am graphing the AC voltage generated by the sensor coil to see what comes out there.

Playing around a bit and putting some ferrous metals near the the whole wannabe :lol: FGM does change the AC voltage of the output. Even putting my hand over the FGM changes the output voltage ... Interesting

Look at the images below running the Franken FGM over hours and putting a screwdriver on top of the coils


No on purpose Disturbance running lonely in the corner. mVAC difference is only 0.3543 mV AC
Image


Yes on purpose Disturbance by putting a screwdriver on top of the coils. Difference is 2.6332 mV AC
Image

If you look closely on the end of the disturbed graph you can see a drop and that was me approaching with the camera to image the mutlimeter screen ...


Now just find out what Gauss values are this :lol: :lol: :lol: :lol: will need to investigate how to measure that in a simple way. Are there simple ways for this ? :shock:

one things leads to the next one :mrgreen:


regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by Carbon60 »

Hi Rainer,
You could make a coil with known inductance and pass a known DC current through it to generate a known magnetic field to calibrate your sensor.

Stu.


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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

Carbon60 wrote: Mon Mar 21, 2022 6:44 am Hi Rainer,
You could make a coil with known inductance and pass a known DC current through it to generate a known magnetic field to calibrate your sensor.

Stu.
Hi Stuart,

Great. Just found the calculators for calculating the Gauss strength for a coil be it linear or toroid. At the moment finished degisgning a toroid for the 3D printer, which I will wind with magnet wire and then test it on my Franken FGM.

This is getting interesting and if the Magnetometer should not work at all at least I learned again a lot about all this magnetic stuff.

:bow2


regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by Carbon60 »

Ha..ha.. It's always good to learn, Rainer. :) Me too.

Stu.


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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

Hi Stuart,

I have sent you a PM

Rainer


regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

UPDATE

Hi,

I know I am reinventing the wheel and the hot water but doing this tests by oneself is very interesting.

Yesterday I built a new Franken FGM using some cheap toroids. 5 in each hole and wound them with 14 turns AWG wire as the primary (excitation coil) and 500 turns samwe wire as secondary sensor coil. This I copied from here

https://www.geotech1.com/forums/attachm ... 1149006588



Image
Image

and below I am changing the magnetic field using another Ferrite toroid wound with 52 turns. No idea how strong the magnetic field is as I am driving the lower coil with my function generator and I do not know the amperage yet. Driving with a Square wave at 0.25Hz at a 25% duty cycle.


Image


and here the result in the multimeter. Need to start my oscilloscope and take a see at how it looks there.


Image


Today I got some other ferrite cores with a permeability value of 5000 which according to the producer is high permeability as Stuart recommended and this one will be would also with primary 14 turns and secondary 500 turns but using 36 AWG wire (this is a very fine wire). I do not count the turns as I go by weight which is easier ;)


Image
Image


It is a big advantage to have a 3D printer as one can instantly print what one needs for things like this.


regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by Carbon60 »

Great work, Rainer. It may be a reinvention, but it’s all about learning and the fun of finding out :)

The paper to which you refer in the link is old, but still it’s an excellent reference.

Wouldn’t the calibration coil be better as a solenoid (long cylindrical) to make the field more linear and uniform? Lots of turns, a steady voltage and known current will produce a stable magnetic field. Ideally your flux gate should fit inside the core of this device.

Nice progress.

Stu.


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Fluxgate Magnetometers (1s and 150s Cadence).
Radio meteor detector.
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Re: Rainer's quest to build a magnetometer

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Carbon60 wrote: Fri Mar 25, 2022 6:06 am Great work, Rainer. It may be a reinvention, but it’s all about learning and the fun of finding out :)

The paper to which you refer in the link is old, but still it’s an excellent reference.

Wouldn’t the calibration coil be better as a solenoid (long cylindrical) to make the field more linear and uniform? Lots of turns, a steady voltage and known current will produce a stable magnetic field. Ideally your flux gate should fit inside the core of this device.

Nice progress.

Stu.
Hi Stuart,

Thanks and I will make a Helmholtz Coil and place the Franken FGM in the center of it.

Step by step nearing to more and more sensitive coils.

I guess I have spent already what a FGM-3 sensor would have cost with freight and taxes to Mexico but where would be the fun ¿? :mrgreen:

Need to order more magnet wire :(


regards Rainer

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Re: Rainer's quest to build a magnetometer

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Hi,

Another step forward.

The first of the two Helmholtz coils is working. According to a calculator I found this coil delivers a magnetic field of 94100 nanoTesla when being excited by 1A and 0.2V.

The new FGM has now 600 turns secondary coil and 14 turns primary coil and two cylindrical ferrite core with a permeability of 5000.

All in all getting more and more interesting

First test arrangement. I guess that is not quite correct as both magnetic fields ara parallel ... Will work on that
Image


This is how the excitation look like. High peak On, Low peak OFF
I still have to find a way to activate the power supply automatically (I will ask a friend to write me an Arduino code) and then record a video of the graph

Image


regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

Forgot to add the link to the coil calculator

https://www.accelinstruments.com/Magnet ... lator.html


regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

Hi,

Helmholtz coil is ready and now test it a while and see how the theoretical calculation of magnetic field fits into reality. I will use my cell phones to measure the µT.

Blue bar is a magnet oriented to North pole.

Basic coils without the table. See the silver screw in the center for adjusting height of the table
Image

Coils with table
Image


regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by Carbon60 »

You've been busy, Rainer.

Stu.


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Fluxgate Magnetometers (1s and 150s Cadence).
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Re: Rainer's quest to build a magnetometer

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Carbon60 wrote: Mon Mar 28, 2022 5:49 am You've been busy, Rainer.

Stu.
Hi Stuart,

Yes and lots of fun. Now in order to compare theory to reality I calculated the magnetic field strength in the center of the coils.

I used the following formulas

Image
Image

Giving the following results and as you can see both are exactly the same

Image


and the reality is different

Geomagnetic field strength in my lab corner more or less an average of the seen values

Image


Adding the Helmholtz coil field to the Geomagnetic field

Image


Substracting the Geomagnetic field from the Helmholtz coil

Image


794 µT minus 768 µT results in 26 µT plus / minus :) I moved the phone in and out in order to find the sensor location in the phone. Both phones gice very similar results.

Now comparing the calculation result to the real result there is a huge difference nearly 2x ...

Theory is 1348 µT and reality is 768 µT as seen in the above image.

Need to find out what happened here ...


regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by Carbon60 »

Hi Rainer,

Either the sensor in your mobile isn’t in the absolute centre of the coil, or the current could be incorrect, assuming the number of turns and diameter are correct. There aren’t so many variables :)

Stu.


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Fluxgate Magnetometers (1s and 150s Cadence).
Radio meteor detector.
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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

Carbon60 wrote: Mon Mar 28, 2022 8:45 pm Hi Rainer,

Either the sensor in your mobile isn’t in the absolute centre of the coil, or the current could be incorrect, assuming the number of turns and diameter are correct. There aren’t so many variables :)

Stu.
Hi Stuart,

I moved the phone inside the coils to find the highest vale and did so with both phones :?

Guess what ? I repeated the experiment and plaing the phone on the inside close to the coils inner diameter I can read up to ~ 1050 µT

Should it not be so that the strongest field is the center ?

Now I am even more confused.


The coil inner diameter resting on the phone edges ...


Image


regards Rainer

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Re: Rainer's quest to build a magnetometer

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Hi,

A few minutes later and look at this. Phone in a different position and now up to ~ 1150 µT getting closer to the calculated value ...

Interesting.


Image


regards Rainer

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Re: Rainer's quest to build a magnetometer

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Hi Stuart,

I was writing in another foum about this Helmholtz coil and something sparked and perhaps I misunderstood how many turns to input.

My coils have 9 turns with a radius of 60 mm and inputting these values in the formula makes the value come closer to the real world measurement.

The phenomena on the higher values on the outer wall I still need to investigate this.


Image


regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

Hi,

OK, after testing different currents and comparing to the theory I can say theory and practice do fit together with of course the normal deviations I have with my rudimentary measuring devices like my cell phones ...

Just ordered a few bipolar hall sensors 49E and DRV5053EA, in order to see how they work and how sensitive they are.

Having some fun ...


regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by Carbon60 »

Great to hear you're having fun, Rainer. It's always interesting to undertake problem solving, especially in a hobby situation.

Stu.


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Fluxgate Magnetometers (1s and 150s Cadence).
Radio meteor detector.
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Re: Rainer's quest to build a magnetometer

Post by Carbon60 »

Hi Rainer,

(Copy/pasted from my other post to keep the information together with your project work)

I find the best source of useable data is from Intermagnet (a global geomagnetic observation network). You can plot out geomagnetic data from a station near you, for whatever date you choose.

https://www.intermagnet.org/data-donnee ... ot-eng.php

I often use their values to 'calibrate' my own charts.

For East-West measurements, use their 'Y' values. To give you an idea of the scale of the expected magnetic declination effect, on a quiet day the range might be of the order of +/- 10 nT, on a day with mild geomagnetic unrest then you might see +/- 20-40 nT and during storms you might see something of the order of +100/-50 nT or similar. These figures depend on your latitude, of course, so nothing is set, but it gives you an idea of how relatively small these deviations are when compared with Earth's magnetic field strength of 25,000- 65,000 nT.

I hope this helps

Stuart


H-alpha, WL and Ca II K imaging kit for various image scales.
Fluxgate Magnetometers (1s and 150s Cadence).
Radio meteor detector.
More images at http://www.flickr.com/photos/solarcarbon60/
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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

Carbon60 wrote: Sat Apr 02, 2022 7:43 am Hi Rainer,

(Copy/pasted from my other post to keep the information together with your project work)

I find the best source of useable data is from Intermagnet (a global geomagnetic observation network). You can plot out geomagnetic data from a station near you, for whatever date you choose.

https://www.intermagnet.org/data-donnee ... ot-eng.php

I often use their values to 'calibrate' my own charts.

For East-West measurements, use their 'Y' values. To give you an idea of the scale of the expected magnetic declination effect, on a quiet day the range might be of the order of +/- 10 nT, on a day with mild geomagnetic unrest then you might see +/- 20-40 nT and during storms you might see something of the order of +100/-50 nT or similar. These figures depend on your latitude, of course, so nothing is set, but it gives you an idea of how relatively small these deviations are when compared with Earth's magnetic field strength of 25,000- 65,000 nT.

I hope this helps

Stuart
Hi Stuart,

Thanks a lot. I have seen that at my site the magnetic earth field varies around 38,000 to 42,000 nT. Both cell phones are quiet similar in their measurements and show that variation from day to day or even sometimes from hour to hour.

Working on something to know how sensitive my new coil is. The new coil has now about 1000 turns on the secondary and 14 turns on the primary using 4 ferrite cores based upon that old paper i mentioned in an earlier message.


regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

I find the best source of useable data is from Intermagnet (a global geomagnetic observation network). You can plot out geomagnetic data from a station near you, for whatever date you choose.

https://www.intermagnet.org/data-donnee ... ot-eng.php

I often use their values to 'calibrate' my own charts.
Hi Stuart,

Just looked into that page and interesting. First I had to fiddle out what the latitude numbers where but then I found out I just need to deduct from the second value 360. North and South are clearly marked via a plus or minus sign.

Unfortunately there are no stations in Mexico (not yet searched for one) and the nearest one is in Fredericksburg, Texas, USA. Will play with that.


regards Rainer

Observatorio Real de 14
San Luis Potosi Mexico

North 22° West 101°
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