Metal resistant compass

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#1
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Dear all
My customer needs a compass that does not change it's output if it's put in a metal case,
Do you have any idea? Can I use the Compass chips from different vendors?

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Which metal is the case made from?

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Compass' are affected by ferromagnetic materials to be more specific.

If the chips use flux gate technology they rely on measureing the earth's magnetic field.

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The problem is that the earth magnetic field is changed by a ferro enclosure. There is no kind of compass that will ignore this because the whole field, itself, is changed.

You can make the enclosure out of non-ferro material, such as brass or aluminum. Maybe stainless steel. But not ordinary steel or iron.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Sounds like you need a "being put into a metal case" detector so you can freeze the output?

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I do not know what goes on in Iran, but in the USA there can be a fairly substantial difference between magnetic and true north.
In the UK, where I live, it is fairly small. Partly because the UK is small.

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The important point in the original post appears to be that Ali's possible customer wants an electronic compass that is not affected by being inside a metal case. Declination was not raised as an issue (though Cliff's animated map IS fascinating).

If the only issue is "metal case", then the ONLY solution is non-ferrous case. There is no sensor that will compensate because the case distorts the magnetic field, itself. The compass just responds to the field that it is in, and that field is distorted. Case made of fiberglass, plastic, kevlar, brass, aluminum, copper, should all be safe. Stainless steel ought to be safe but I have no personal experience, there. What is NOT safe is plain steel and cast iron.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Thanks Cliff, that's spectacular!

Some stainless depending on grade, is ferro-magnetic, as is some 60/40 solder from experience...

The metal on SMD parts is also, try picking up the parts with a magnet, but don't use them after that on a PCB with a compass...

In cases where you have nearby metals you can apply both hard-iron and soft-iron correction. Hard-iron is pretty straight forward but soft-iron gives me nightmares.

Some hard-iron correction code as part of a tilt compensation library here:
http://krazatchu.ca/2012/02/27/6...

Last Edited: Wed. Jul 3, 2013 - 01:27 AM
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Jim, there's various grades of stainless steel- some ferromagnetic ' some not. The other way of determining direction that isnt affected by local magnetism is to use a dual GPS receiver. This will tell you direction even when standing still. You'll get your absolute location and the time as well.

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I doubt that soft/hard iron correction will work well for a compass inside a metal enclosure. That said -

I have seen compasses on a ship's bridge. Not exactly a metal enclosure but pretty close to it. With correction, the compass is still usable.

There are also gyro compasses that align themselves with the earth's spin axis. No metal correction needed. But, they also do not sense the magnetic field. So, if this "compass" is to be used for anything else beside navigation, then it might not be suitable.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Dear all
Thanks for your answers, actually the compass will be used for navigation, it should be reasonably cheap, because my customer needs to mass product it, and It will be used in a Iron case, So know what should I do? do we have reasonable solutions?

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Apart from magic, you need to make a compromise.

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Quote:
Apart from magic, you need to make a compromise.
I did not get your point :)

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You can not use a magnet in or even near a iron case. It has to be in something else. There is NOTHING you can do about it, physics. Bare in mind, that it also has to be quite far from motors and other such equipment that has magnets in it. To get a reasonably good compass that can be used for navigation it has to be at least 10m away from anything steel/iron (including cars etc).

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Change Planck's constant and as if by magic the compass will work inside an iron enclosure.

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Quote:
Change Planck's constant and as if by magic the compass will work inside an iron enclosure.

what?

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He is joking. Planck's constant is one of the fundamental constants of our universe. Sort of like the speed of light (in vacuum) - it is a fundamenta constant. More here: http://en.wikipedia.org/wiki/Pla... . If you were able to construct a universe where Plancs constant was different, that universe would behave differently from ours.

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I think the customer would also like the following:
Left handed screwdriver
Striped paint
Long weight

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No magnetic compass will work inside an iron box. That is because the iron, itself, distorts the magnetic field. Most of the field will stay in the iron and not even go into the central part of the box. You cannot measure what is not there.

Options are:

1) different material than iron

2) non magnetic compass such as gyro compass

That is about it.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Dear Jim
Thanks for the options, so which gyro compass do you suggest? Can I use the Silicon gyro chips? like analog devices or ST chips?

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Not likely.