Detecting magnetic field changes over a large area

Using Arduino Project Guidance
1

Greetings,

I am very very new to magnetic fields and study. I have been thinking about building a senor net that would cover a large area, be low voltage (solar / battery), but also be high res enough to be useful.

Like Adafruit Triple-axis Magnetometer, there is one that is "wide" and one that is not so wide. Paired with a GPS (or would it be better to have more than one, like 3 equally dispersed).

My question about these types of sensors - if you had more than one in a grid, can you use the output from each to get better readings overall?

If I wanted to monitor an 80 acre area that is mostly line of sight, what kinds of sensor placement and density should i consider?

I am afraid i dont know enough to know what kind of density i would need to create measurement wise to have accurate meaningful data. My thought with more a dispersed set of arrays that could relay data back to a pi is that the combination from several different sensors would give me a better picture overall. I remember hearing that the gas/oil industry use like 900Mhz transmitters to relay. Can something like that be achieved using ardunio for the sensor management and relay of data back to the PI? but over distances that could approach .5 miles or .75 miles. Can you do mesh?

I am not afraid to read the manual. I was hoping for some ideas about how to calculate my power requirements for the individual sensors and ardunio to store/forward, something i am not good at, at all :frowning:

An idea of what kinds of transmitter to use in an outdoor hostile (northern maine winters) environment:

What kind of housing should i consider? Either staying away from conductive metals or synthetic?

Should I consider having a low power heater or just shut down if -32f or temps exceed environmental specs? How do you harden for environment? Fiberglass insulation wouldnt impact would it?

What kinds of transmitters i should look at for transmitting over open (or slight obstructions) ground, resistant to humidity / rain / snow / ice (friends have told me that lower range communications can fade during heavy rains). Is there an antenna design that would achieve this?

Lastly, if i wanted to measure watts of power being given off or electric field charge of the atmosphere at those sites what are good sensors for those kinds of measurements.

What am I missing? What should I be reading?

Thank you! Thank you! Thank you in advance!!!

John

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what's the source of your magnetic field changes? are we talking natural stuff (Geological Activity, Mineral Deposits / Magnetic Anomalies, Solar activity like solar flares, ...) or Human Activity driven (Electrical equipment, power lines, Mining, ...)

Unless you are in a very specific area, for natural events they tend to be quite spread out

I would say that for a pretty dense coverage you would go for one sensor every 25 m but could likely go lighter with one every 50m or even100m for broad, general monitoring.

80 acres is about a square of 600m x 600m, so if you have one every 100m you would need 49 sensors (of course can vary with the geometry of the field)

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Thanks! I am interested in detecting flux in the earths field, strength, polarity, etc… I really want to measure impacts of solar winds and other sun based phenomena on earths magnetic fields.

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you could look at 3-axis magnetometer like MAG3110 or LIS3MDL based modules and see if their spec match your needs.

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If you didn't place them along the outer border, your 49 sensors can be placed at 75m increments:

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Can probably be paired with ESP8266 and set to use ESP-Now set to transmit data on a schedule so those transmissions disturbances can be accounted for and filtered out.

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Fair point

1 Like
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I have to wonder how many miles away are the AC power lines for your field.

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Some practical experience with consumer grade magnetometers.

For one, they all have to be individually calibrated, as measurements made "out of the box" have large offsets and significant scale factor errors.

Second, the sensors are temperature sensitive, and out of doors, you will see large changes in readings merely due to temperature changes.

Best overview and tutorial on calibrating magnetometers: Tutorial: How to calibrate a compass (and accelerometer) with Arduino | Underwater Arduino Data Loggers

Buy a couple of different ones and spend some time getting acquainted before deciding whether this idea will work at all.

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Thank you very much!!! Will do!!

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Ah, I have power lines and a road that bi-sect the area I was wanting to monitor… so if I had an array in that area, I would need to measure and get a “normal” then measure deviations?

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Thank you!! I am curious if having a “cluster” of sensors could be used to achieve higher resolution in sensor sites, how can I tell the optimum spacing of the sensors for overlap, or am I thinking about this wrong?

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First, define "meaningful data".

Please explain what you hope to learn from the proposed huge amount of effort, and why a "large area" is important.

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That’s awesome!! Thanks!!

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Ever try to see the stars in a city, or try to have a meaningful conversation at a rock concert? Depending on the traffic and the types of power lines, you may not have much of a chance of discerning discrete changes or building meaningful data.

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Even a simple multiturn wire loop will detect the magnetic field from your power lines from a thousand feet away. That field is constantly changing and will overload any magnetic field sensor.
In addition, ALL vehicles on your road are moving magnets,

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The polarity of the Earth's magnetic field only changes every 300,000 years or so, therefore there is little point measuring that.

See this link for a discussion about the rest:-

The field strength is unlikely to change much either. In fact the field is a vector and so measuring the strength is a bit meaningless. It is the vector you need to measure.

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Meaningful, its just a hunch to me, I don’t know what all I would learn but I suspect depending on the sensitivity of the individual chips I might be able to detect geomagnetic disturbances localized and dispersed that I may be able to tie to events using data from other sources like SWARM or NASA.

Or If these are sensitive or I can build an array sensitive enough to detect the presence of life in a given area, or movement just by tracking electromagnetic fields. Low flying aircraft? Other anomalies IDK really it was something that occurred to me might be beneficial to know and study. Could I increase the range by suspending aloft via balloon? I have a weather station too, I honestly want to become mostly data independent I realize localized magnetic monitoring might not yield data that could be extrapolated up to a global scale (meaningful at that scale) but would maybe help me detect things on my own around my property.

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Yikes! How can you get around that? You cant really filter those out if you want to detect spikes in those ranges ? If I was plotting on a heat map those would be “Dead zones then” not because of lack of signal but because of too much.

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Ah man… https://imgur.com/a/magnetic-drop-off-LrjSCtN

Eh, NASA and the ESO cant seem to agree and I am to the point of wanting to monitor it for myself. What I am seeing using their data is a drop off of about 20k nT in 4 years (comparing max field values). Their revised projections and the reaction earlier this year in May makes me think we might be off a bit on our strength and drop off projections and they may be accelerating.

I figured using several sensors in a cluster per site over a large space would allow me to detect changes, but it sounds like I would need to put my arrays aloft to get away from ambient fields that might be too strong to filter.

Boo… I live in a remote place but not so remote as to be away from powerlines.

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Short answer, move the array very far away. I don't see how the project is at all practical. Even if you had a magnetically stablish area, it would still be tough to produce meaningful data beyond localized changes. Probably not much on the global scale or beyond.