Measure Earth Magnetic Field using Hall Effect

Thread Starter

MrsssSu

Joined Sep 28, 2021
199
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Hi all :),
This is about Hall Effect from here. The voltage across a metal will change based on the strength of the magnetic field. I am wondering whether this will be accurate in reading small magnetic field such as the earth's magnetic field to point to the NORTH. From my knowledge, since the earth magnetic field is small and weak, it is very difficult to read on a multimeter, so perhaps we can amplify that small voltage to a big voltage by using op-amp. Is this a possible solution because I am trying to make my own DIY magnetometer :)?
 
Last edited:

MrSalts

Joined Apr 2, 2020
1,762
View attachment 264160
Hi all :),
This is about Hall Effect from here. The voltage across a metal will change based on the strength of the magnetic field. I am wondering whether this will be accurate in reading small magnetic field such as the earth's magnetic field to point to the NORTH. From my knowledge, since the earth magnetic field is small and weak, it is very difficult to read on a multimeter, so perhaps we can amplify that small voltage to a big voltage by using op-amp. Is this a possible solution :)?
It depends on the threshold magnetic field that your sensor can sense. After that, you can simply compare output when positioned north/south vs east/west. Many Hall effect sensors can sense the earth's magnetic field. Try Google for some examples.
 

Thread Starter

MrsssSu

Joined Sep 28, 2021
199
It depends on the threshold magnetic field that your sensor can sense. After that, you can simply compare output when positioned north/south vs east/west. Many Hall effect sensors can sense the earth's magnetic field. Try Google for some examples.
Hi sir, I mean I want to try to make it myself rather than just buying out of curiousity :)
 

Thread Starter

MrsssSu

Joined Sep 28, 2021
199
Hello there, :) there are plenty examples on the internet this is only one. I picked it cuz it looks fun to make and easy.
In doing so it can also be modified to conform to your criteria with a high degree of success.

https://www.electroschematics.com/magnetic-field-meter/
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Hi sir, thank you for your reply. This circuit looks like it can measure weak magnetic field such as earth's with only using inductor coil to gather magnetic field and without using Hall-Effect special material plate? And, shouldnt the inductor coil must be rotated or moved in order to generate current from cutting magnetic field lines. The link does not say that haha:)
 
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Delta Prime

Joined Nov 15, 2019
1,326
That was only an example. Let's concentrate on what you would like to accomplish.
You wish to measure the earth magnetic field incorporating operational amplifiers with hall effect sensors .a circuit capable of detecting (if memory is correct ) around 50 micro Teslas.The visual display can be either analog or digital & will be proportional to the intensity of the magnetic field of the Earth. all you have to do is walk around in an open area away from buildings.
We have the Chinese to thank for this about 1000 or 2000 years ago BC!
When someone had the idea of winding a piece of silk thread around a piece of magnetite ( a Rock)
for navigation so they don't get lost.
The very first compass! {As a side note}
Because of my youth this is the first time anyone has called me sir. thank you for that! :)
I have to go to work now but I'll be back later I hope.
 

DickCappels

Joined Aug 21, 2008
8,710
It works like a fluxgate magnetometer (Google that one!). I have only seen electrically sensing the earth’s magnetic field done reliably with a fluxgate.

When I tried to use a Hall effect device I found it not sensitive enough and way too noisy for such an application. Maybe if I felt like spending many more hours on it I could have made it work.
 

nsaspook

Joined Aug 27, 2009
9,740
It works like a fluxgate magnetometer (Google that one!). I have only seen electrically sensing the earth’s magnetic field done reliably with a fluxgate.

When I tried to use a Hall effect device I found it not sensitive enough and way too noisy for such an application. Maybe if I felt like spending many more hours on it I could have made it work.
The fluxgate is about as good as it gets for a classical magnetic field detector.
https://en.wikipedia.org/wiki/Magnetic_anomaly_detector

https://www.imperial.ac.uk/space-an.../fluxgate-magnetometers/how-a-fluxgate-works/
https://www.latimes.com/science/la-me-vacquier24-2009jan24-story.html
 

Thread Starter

MrsssSu

Joined Sep 28, 2021
199
Hi, in this video here which is similar to the article that you posted. So, we just have to put AC square wave current through the drive winding ,and if there is no magentic field that is going into the toroidal core, the sense winding will not sense current. and, if there is, it will be able to get a voltage reading, right ? :)1649131816067.png
 

Tonyr1084

Joined Sep 24, 2015
6,891
I don't really have any experience in this area other than a company I worked for decades ago. They built a magnetometer that was to live at the bottom of an oil well DURING DRILLING. The purpose was to detect magnetic north. An off-shore oil rig could sink up to (if memory serves) 300 wells without having to move the rig. It's done by steering the bit via Jetting. That subject is not germane to this conversation. The magnetometer they built had three accelerometers to detect the angle of the drill bit. A magnetometer made from some number of coils was then rotated until it detected magnetic north at its max potential. The thing I most remember of the tool was its calibration. The cal shack was made of all wood construction and had stainless steel fasteners so as to not introduce any magnetic deviation in earths magnetic field. Anyone working in the shack had to leave all potential sources of magnetic disturbances in lockers in the main building some 50 feet away from the shack. The shack was also located well away from the parking lot.

There was some kind of report that they got every day concerning the wandering magnetic field of earths magnetic flux. Yes, annually, there was deviation in earth's magnetic north by some few degrees. As memory suggests, August was typically the time when magnetic north deviated the most. During certain times of the year magnetic flux was so far off that the tools could not be calibrated accurately. I believe since then they've developed some sort of compensation for that, but like I said early on, it's been decades since I worked there.

Other factors also can affect magnetic north sensing such as iron content in the landscape. On the Connecticut shore of the Long Island sound you couldn't use a metal detector due to the high iron content in the ground. I tried treasure hunting along Norwalk, Milford and New Haven with no found treasures. Only a whole lot of digging in iron rich deposits that affected the magnetic reflectance of the detector. In real-estate they say the most important factor is "Location Location Location". So it is also true where you plan on using this sensor. The more sensitive it is the more influence you'll experience in deviations of the magnetic fields.

That's all I got for you.
 

Tonyr1084

Joined Sep 24, 2015
6,891
@ci139 Now that you mention it - Triaxial fluxgate gradiometer of high stability and linearity - I recall the coil having three different windings all in different orientations. One coil (essentially) North/South, another East/West and a third Horizontal. All wound within each other.
 

DickCappels

Joined Aug 21, 2008
8,710
I once took over technical supervision of a high resolution monitor project from an engineer who once worked for a company that made magnetometers. The problem he had to solve was how the monitor would know when it was turned in the earth's magnetic field because with the very high resolution phosphor dot pattern without degaussing after the monitor was turned the colors would change because the red, green, and blue beamlets would land on the wrong phosphors.

His solution was to watch the ambient magnetic field with a fluxgate magnetometer. The monitors were built in Italy in a factory that had a railway line running next to the building. Every time a train passed by every monitor in the place would degauss itself. It was an awsome sight.

But there is more. In an office environment if you opened a file cabinet anywhere near the monitor it would degauss itself. Moving a desk chair closer to the monitor could set it off. As clever and creative as the solution was, there were so many complaints from the field that we wrote up instructions for defeating the magnetometers. They were just a little too sensitive.
 
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