Geomagnetic vectors

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Hi,

I'm starting a new project in which I need to use the World Magnetic Model (WMM 2010) and read the magnetic components of the Earth magnetic field such as field intensity in nT, inclination, declination etc. How can this be accomplished using digital electronics? Are there integrated circuits that read those components?

Thanks in advance! :)

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so that probably will be a combo of an acelerometer and a magnetic sensor.
use a load of math on the output of those and you have what you need.

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I think that a little more description is needed to get any real help here ( my opinion).

But, just guessing, a hall effect sensor of the right type could provide you the magnetic intensity. You then need something to determine which direction and vertical angle you were measuring. Not sure what that would be.

Plus you need to know your location (GPS?)

Maybe there are packaged solutions to your problem, but somebody smarter than me will have to talk about them. FWIW, I don't think that you will find a set of ICs that can handle this.

I had not heard about the WMM -- interesting project.

hj

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Yes., need more information.
Is the question,
a) what is the magnetic field strength/orientation according to the WMM model at location x ?
or
b) what is the actual (real) magnetic field strength/orientation at location x ?

a) can be done by feeding latitude/longitude/altitude (eg via GPS) into the WMM model.
b) can be done with a 3-axis magnetic sensor (eg HMC5883) and an attitude indicator (accelerometer), and correcting for the local hard/soft-iron effects and inclination.

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To determine the magnetic vector components, you need to know the orientation of the sensor. An accelerometer can help but it will only provide vertical orientation. But, you can rotate about the vertical axis, and the accelerometer will tell you nothing about orientation.

So, what kind of sensor will provide the other information? A gyro compass, maybe?

Jim

 

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I thought the electronic compasses were a couple of coils at 90 deg. I guess you could make a 3 axis magnetometer too.

Imagecraft compiler user

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two compasses would get you three magnetic vectors.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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ka7ehk wrote:
two compasses would get you three magnetic vectors.

Jim

Hi Jim,

Could you tell me what three magnetic vectors can you find with two compasses?

Thanks in advance.

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Put one in the horizontal plane. You get X,Y components relative to (in the plane of) the plane of the sensor.

Put the second one in a vertical plane parallel to one of the axes of the first sensor.

That gives you the Z axis and a comparison with one of the first two axes, so that you can scale them together.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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ka7ehk wrote:
Put one in the horizontal plane. You get X,Y components relative to (in the plane of) the plane of the sensor.

Put the second one in a vertical plane parallel to one of the axes of the first sensor.

That gives you the Z axis and a comparison with one of the first two axes, so that you can scale them together.

Jim

Interesting, well that will give me the direction of the components of the magnetic field. But what about the magnitude of those vectors?

Have anyone used a digital magnetometer? Are they capable of reading the X, Y and Z components of the geomagnetic field?

Thanks in advance.

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I guess with a compass, you only need to resolve an angle with no interest in the magnitude. Unless you can also read the effective magnitude of each component. Even then, it would all be relative (uncalibrated). You probably want a bit more than that.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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an accelero meter gives you the angle on the gravity vector. So you know when you are flat on the ground or not.
that is a scaled number depending on the gravity measured.

an magnetic sensor give you an angle on the magnetic field.

never used one, but an altimeter for what I know gives the barometric pressure that can be used to calculate a hight difference between the set value (being 0 or a known altitude at start) and the current value.

GPS gives the location data, note that if you want to do very exact measurements you might need special receivers that are not commercially available to ensure accuracy of location.

so in the end all sensors give a set of vectors and not hard values. You need to do math to get the values from the vectors.

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We use a 3-axis magnetic sensor and a 3-axis accelerometer in conjunction to calculate direction and slant of the tool. I can't be too specific, except to note that things get hairy around vertical. The grid dip is significant, too, depending on latitude.

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Lots of postings, but no mention of something like: https://www.sparkfun.com/product... The Razor has 3-axis gyro, accels, and compass.

The OP really hasn't stated what he is actually trying to do. The accels are needed to determine actual orientation, since the WMM model generates values that are referenced to local NED plane, so that the compass readings can be correlated to the predicted values from WMM.

What accuracy is required? WMM is probably only accurate to ~0.5 deg, which is in addition to the compass measurement and orthogonality errors.

The processor in the Razor is probably not beefy enough to run WMM at high speeds, and probably can't run EMM even at low speeds, so bear that in mind.