Rainer's quest to build a magnetometer

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Rainer's quest to build a magnetometer

Post by Carbon60 »

rsfoto wrote: Tue Mar 15, 2022 3:30 pm
Carbon60 wrote: Tue Mar 15, 2022 3:28 pm
rsfoto wrote: Tue Mar 15, 2022 3:19 pm Hi Stu,

Every time I see those graphs my finger itches but having too much steel surrounding the area I get over it ...

I already have a problem with my Lightning detection system and my electric fence :mrgreen:

Very interesting.
Hi Rainer,
It’s a real shame. It’s great fun to see the effects of space weather rolling along on my computer screen as the data stream in.

Stu.
Hi Stu,

Question. Is there a simple way to measure it for testing my environment before I dig deep into my pocket ?

I have time and nothing to do as a retiree ... :lol:

... and I have a 3D printer so I can print the necessary parts ...
Hi Rainer,
The sensor is 60 euros and for a trial you can run it off a simple battery to provide a stable voltage input. You could print a plastic housing for the sensor and bury it in your garden connected to a battery from your observatory. The output from the sensor could be connected to your SDR input (used for detecting meteors) via a resistor pair to drop the voltage way down to a few microvolts. Tuning the SDR to the output frequency of the sensor will show up as a line on the spectral waterfall. This should remain quite static under normal times and should shift up and down in frequency during a solar storm. If you do all this and the frequency shifts excessively even during quiet times, then your magnetic environment is probably not suitable.

This is the simplest way I can think of testing your environment using (mostly) the kit that you already have.
Sensors can be purchased here:
https://magnetometer-kit.com/product/f ... ld-sensor/

Stu


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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Rainer's magnetometer build

Post by rsfoto »

Carbon60 wrote: Tue Mar 15, 2022 4:14 pm
rsfoto wrote: Tue Mar 15, 2022 3:30 pm
Carbon60 wrote: Tue Mar 15, 2022 3:28 pm

Hi Rainer,
It’s a real shame. It’s great fun to see the effects of space weather rolling along on my computer screen as the data stream in.

Stu.
Hi Stu,

Question. Is there a simple way to measure it for testing my environment before I dig deep into my pocket ?

I have time and nothing to do as a retiree ... :lol:

... and I have a 3D printer so I can print the necessary parts ...
Hi Rainer,
The sensor is 60 euros and for a trial you can run it off a simple battery to provide a stable voltage input. You could print a plastic housing for the sensor and bury it in your garden connected to a battery from your observatory. The output from the sensor could be connected to your SDR input (used for detecting meteors) via a resistor pair to drop the voltage way down to a few microvolts. Tuning the SDR to the output frequency of the sensor will show up as a line on the spectral waterfall. This should remain quite static under normal times and should shift up and down in frequency during a solar storm. If you do all this and the frequency shifts excessively even during quiet times, then your magnetic environment is probably not suitable.

This is the simplest way I can think of testing your environment using (mostly) the kit that you already have.
Sensors can be purchased here:
https://magnetometer-kit.com/product/f ... ld-sensor/

Stu
Hi Stu,

One question. Would a wound copper coil do the same thing as a FGM sensors eg. measure the movement of the magnetic field ? or do I need something else like a second coil with a excitation frequency ... I think I remember I read something like this ...

From my lightning system I still have two unused ferrit coils which came as antenna but as I made my own lightning detecting antennas they are just collecting dust ...

SDR, I have a spare one. Which is the frequency we are talking about ? The SDR I have has a range from 24MHz to about 1.766 GHz ...

Let me check as I remember there is a way to go below that.

Just guessing ...


regards Rainer

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Re: G2 Geomagnetic Storm (CME Impact) 13th-14th March 2022

Post by Carbon60 »

Hi Rainer,
The FGM sensor is very sensitive. It presents an output signal of +5 volts as a square wave with a frequency of typically 60 kHz when oriented east-west. The frequency shifts up and down according to the strength of the local field. Mine detects nT scale changes. The applied voltage and ambient temperature also influence the output frequency, so these have to be carefully controlled to avoid erroneous results. I don’t know if a copper coil will be a suitable substitute, although it might be a suitable means of determining how noisy the magnetic environment is in general, as a starting point.

Stu.


H-alpha, WL and Ca II K imaging kit for various image scales.
Fluxgate Magnetometers (1s and 150s Cadence).
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More images at http://www.flickr.com/photos/solarcarbon60/
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Re: G2 Geomagnetic Storm (CME Impact) 13th-14th March 2022

Post by rsfoto »

Carbon60 wrote: Thu Mar 17, 2022 4:22 pm Hi Rainer,
The FGM sensor is very sensitive. It presents an output signal of +5 volts as a square wave with a frequency of typically 60 kHz when oriented east-west. The frequency shifts up and down according to the strength of the local field. Mine detects nT scale changes. The applied voltage and ambient temperature also influence the output frequency, so these have to be carefully controlled to avoid erroneous results. I don’t know if a copper coil will be a suitable substitute, although it might be a suitable means of determining how noisy the magnetic environment is in general, as a starting point.

Stu.
Hi Stu,

Thanks. Yesterday I did a bit of homework and made two coils (printed two cylinders which fit over the round ferrite antenna) with opposite windings and in the center I put my ferrite antenna and played with my function generator as well as oscilloscope.

The excitation of the sensor coil works OK but still need to find out how the magnetic field changes and for that I have a strong magnet. Need to read more about that.

Will also start to play with Hall sensors. I also have some toroidal coils I bought some time ago. Will make a case and wind two opposite coils on that too and see how that shishkebab works.

In the meantime I already contacted the guys from the FGN sensors. All in all that would be an investment of about US $ 100.00

60 kHz is not measurable with the SDR I have. Minimum is 500 kHz. Perhaps using an Arduino ? Need to investigate this.

Later on today I can post some images of the setup.


regards Rainer

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Re: G2 Geomagnetic Storm (CME Impact) 13th-14th March 2022

Post by Carbon60 »

Sounds interesting, Rainer. It will be fascinating to follow your progress.

Stu.


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Fluxgate Magnetometers (1s and 150s Cadence).
Radio meteor detector.
More images at http://www.flickr.com/photos/solarcarbon60/
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Re: G2 Geomagnetic Storm (CME Impact) 13th-14th March 2022

Post by rsfoto »

Carbon60 wrote: Fri Mar 18, 2022 6:15 am Sounds interesting, Rainer. It will be fascinating to follow your progress.

Stu.
Hi Stu,

Can we keep posting my findings here or should I start a new posting ?

BTW I seen to have an understanding problem. Looking at all the info in the www i remember having read once that one needs to have to opposite wound coils but looking at all the drawings I see normal wound coils.

Anyhow I will experiment with my coils and my function generator in order to see how all this behaves.

;)


regards Rainer

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Re: G2 Geomagnetic Storm (CME Impact) 13th-14th March 2022

Post by Carbon60 »

rsfoto wrote: Fri Mar 18, 2022 4:21 pm
Carbon60 wrote: Fri Mar 18, 2022 6:15 am Sounds interesting, Rainer. It will be fascinating to follow your progress.

Stu.
Hi Stu,

Can we keep posting my findings here or should I start a new posting ?

BTW I seen to have an understanding problem. Looking at all the info in the www i remember having read once that one needs to have to opposite wound coils but looking at all the drawings I see normal wound coils.

Anyhow I will experiment with my coils and my function generator in order to see how all this behaves.

;)
Hi Rainer,
I’m happy for you to continue here, but it might be helpful to start a new thread to more easily track it down in future.

Stu.


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: G2 Geomagnetic Storm (CME Impact) 13th-14th March 2022

Post by rsfoto »

Hi Stuart,

OK. Yesterday I fooled myself and now I turned around the shishkebab using my ferrite antenna as the excitation coil and my two opposite wound coils as sensor.

I am feeding a square wave with 1 MHz to the coil with the ferrite center. Using the two opposite wound coils as sensors ( 87 turns with 20AWG magnet wire 0.75mm Ø) and the measured DC voltage with my digitial multimeter is 0.00mV. Measuring the AC of the sensor coils gives me a value of 82.5 mV when feeding the square wave with 1V peak to peak.

Now when I pass a magnet (salvaged from a hard disk drive = quite strong) over the sensor coils I am able to measure up to 2.0 mV. Doing so with a single wound coil gives the same result.

My function generator has a step up and step down delay on a square wave of 70 ns measured at 1 MHz square wave. Yellow line on oscilloscope and magenta line is the AC curve of the sensor coils.

I orderered yesterday a roll of 28 AWG (0.3mm Ø) magnet wire which is much finer and I will wind a few hundred turns on the sensor coils. I guess the finer the wire and the more turns I apply the higher the voltage will be.

Next step is my toroid coil with a sensor coil and wee what happens with that. Maybe I can salvage from a loudspeaker a coil.

I guess my rudimentary Flux Gate magnetometer is working.

Below the setup and sorry for the mess, but that is the only way I find the stuff I need :mrgreen:


Image
Last edited by rsfoto on Fri Mar 18, 2022 7:38 pm, edited 1 time in total.


regards Rainer

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Re: G2 Geomagnetic Storm (CME Impact) 13th-14th March 2022

Post by rsfoto »

Just tested my toroid coil with a sensor coil, of course too few turns as well as too thick wire but that was a rest I had laying around here.

Same result but the DC voltage was by far much less and maximum achieved was 0.35 mV when passing the magnet over the whole enchiladita (diminutive in spanish for enchilada) :shock:


Image


regards Rainer

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Re: G2 Geomagnetic Storm (CME Impact) 13th-14th March 2022

Post by rsfoto »

Hi,

Sorry for the monolog but just remembered my multimeter can graph events over time and here two artificial Geostorms on the bench

:lol: :lol: :lol:


Image


Image


regards Rainer

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Re: G2 Geomagnetic Storm (CME Impact) 13th-14th March 2022

Post by rsfoto »

Carbon60 wrote: Fri Mar 18, 2022 6:10 pm
rsfoto wrote: Fri Mar 18, 2022 4:21 pm
Carbon60 wrote: Fri Mar 18, 2022 6:15 am Sounds interesting, Rainer. It will be fascinating to follow your progress.

Stu.
Hi Stu,

Can we keep posting my findings here or should I start a new posting ?

BTW I seen to have an understanding problem. Looking at all the info in the www i remember having read once that one needs to have to opposite wound coils but looking at all the drawings I see normal wound coils.

Anyhow I will experiment with my coils and my function generator in order to see how all this behaves.

;)
Hi Rainer,
I’m happy for you to continue here, but it might be helpful to start a new thread to more easily track it down in future.

Stu.
Hi Stu,

Sorry did not see this answer and yes thst is better

The moderators should be able to split the topic and make a new topic out of my answers.

Moderators ? Please and thank you

:bow2


regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by Montana »

That a was a trial and half, hope I haven't lost anything? you can change the title if you like :)

Alexandra


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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

Hi Alexandra,

Great and Thanks a lot and the title is perfect as it sounds like " Search for the Holy Grail " :lol:

:bow2


regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

... and the Waltz goes on

https://www.youtube.com/watch?v=1LGVGekPSzo

I found a dead motor and unwound one of the poles. In total it gave me now a coil of exactly 5.5 Ohm. This means I need to increase the sensor coil or test what it means with a stronger excitation to see if that increases sensitivity too. :?:

Now I even detect the magnet disturbance in the oscilloscope line ...

Next step is to build an amplifier and see what is detected.


Image


Image


Here some artificial Geostorms :mrgreen: seen in the oscilloscope as well as in the multimeter graph.


Image


Image


regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by DeepSolar64 »

Interesting, Rainer and Stuart. I'll certainly follow you on this.


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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

DeepSolar64 wrote: Sat Mar 19, 2022 1:44 am Interesting, Rainer and Stuart. I'll certainly follow you on this.
Hi James,

This sort of experiments happen when a retired Engineer has nothing to do :lol:

I think I am reinventing the wheel, the black thread and warm water :mrgreen:

.. anyhow it is interesting ... and keeps my brain clocking ...

;)


regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by DeepSolar64 »

Rainer,
I knew you had an engineering background somehow. I have some familiarity with electronics since I work in the lighting industry but it's limited. I hope you make this work. I like seeing people get off the beatened path on learning about the Sun. Magnetometry and spectroscopy, spectroheliography included, are certainly two fields amateurs can expand on. Good luck on your project.

James


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Re: Rainer's quest to build a magnetometer

Post by Carbon60 »

Great progress, Rainer. You have lots of really nice toys to play with in your workshop/laboratory there :mrgreen: :mrgreen:

My only concern is sensitivity. In your workshop the magnetic environment will be really noisy at the nT level, so the oscilloscope output should be bouncing all over the place from magnetic fields created from all that electrical equipment. What do you see in the screen at the micro volt level?

Are you using a high permeability alloy core?

Stu.


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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

Carbon60 wrote: Sat Mar 19, 2022 6:35 am Great progress, Rainer. You have lots of really nice toys to play with in your workshop/laboratory there :mrgreen: :mrgreen:

My only concern is sensitivity. In your workshop the magnetic environment will be really noisy at the nT level, so the oscilloscope output should be bouncing all over the place from magnetic fields created from all that electrical equipment. What do you see in the screen at the micro volt level?

Are you using a high permeability alloy core?

Stu.

Hi Stu,

Yes I have put together all that stuff as sometimes I have some ideas and for realizing them you need that equipment. Long time ago I built my own Sun guider as well as I am working on a vibration sensor for the equatorial mounts, etc.
What do you see in the screen at the micro volt level?
The peaks you see in the graphs were induced by passing a magnet over the FGM. Let me run the graph of the multimeter for a few minutes, which I did yesterday but did not take an image. It graphs a random curve in the µV range. Will post an image later.
Are you using a high permeability alloy core?
No idea as I bought those already wound toroid coils maybe 2 years ago or something.

I also bought some unwound toroid cores but winding them is a PITA and how much wire should I wind on them in order to use them as excitation coils.

¿ Would it be easier to use bars instead of toroid cores ? I have seen they are not cheap :o

One question. How do I have to orient the magnetic field of the sensor coils in regard to the Earth magnetic field eg. the sensor coil North-South and so the magnetic field is oriented East-West ? Thanks

istockphoto-596085992-1024x1024.jpg
istockphoto-596085992-1024x1024.jpg (95.88 KiB) Viewed 2090 times


regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by rsfoto »



regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by Carbon60 »

Hi Rainer,
Best to measure the east-west field vector.

Stu.


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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

Carbon60 wrote: Sat Mar 19, 2022 6:41 pm Hi Rainer,
Best to measure the east-west field vector.

Stu.
Hi Stu,

But how do I need to orient the coil eg. the magnetic field of the coil to the earth magnetic field ?

:?

Orient 1


Image


Orient 2


Image


regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

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


regards Rainer

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Re: Rainer's quest to build a magnetometer

Post by Carbon60 »

rsfoto wrote: Sat Mar 19, 2022 8:13 pm
Carbon60 wrote: Sat Mar 19, 2022 6:41 pm Hi Rainer,
Best to measure the east-west field vector.

Stu.
Hi Stu,

But how do I need to orient the coil eg. the magnetic field of the coil to the earth magnetic field ?

:?

Orient 1


Image


Orient 2


Image
Hi Rainer,
Good question. The windings should be oriented like this:
https://www.imperial.ac.uk/ImageCropTo ... 86_x2.jpg

The toroidal coil horizontal, with the east-west magnetic field vector passing through the sensor coil as per orientation 1. In other words, the External Field vector in the east-west direction (H in the diagram) should be parallel to the core axis through the sensor coil.


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Re: Rainer's quest to build a magnetometer

Post by Carbon60 »

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.


H-alpha, WL and Ca II K imaging kit for various image scales.
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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:


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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


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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


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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.


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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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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

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 :(


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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

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


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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


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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


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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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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

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 ...


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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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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


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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

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


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Re: Rainer's quest to build a magnetometer

Post by rsfoto »

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


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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 ...


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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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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


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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.


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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

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