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After experiencing difficulty with navigation, it turned out that my Silva magnetic compass (Ranger 3 model) had become repolarised the wrong way round. I switched to a old compass and this also suffered the same fate. Meanwhile polarity of the first one has returned to the right way round. Something is de/re-polarising my compasses. I have not conducted any tests, but a likley culprit is my mobile phone which I usually put in the top pocket of my rucksack along with the compass.
Silva have offered to repolarise the compass at their premises in Livingston.
See also:
http://www.ukclimbing.com/forums/t.php?t=421303
http://www.ukclimbing.com/forums/t.php?t=420223
Silva have offered to repolarise the compass at their premises in Livingston.
See also:
http://www.ukclimbing.com/forums/t.php?t=421303
http://www.ukclimbing.com/forums/t.php?t=420223
In reply to Roland Ascroft:
Is it a complete and accurate 180 degree change and is it instantaneous or gradually changed?
Is it a complete and accurate 180 degree change and is it instantaneous or gradually changed?
In reply to Roland Ascroft: It's likely to be the phone. I was using my GPS phone next to my compass recently and noticed quite a shift when held together.
In reply to Roland Ascroft: slider phones often have a magnet in them paired with a magnetic switch to detect if its open or closed (rather than a traditional switch that would be more subject to dirt causing premature wear), that could be an issue.
In reply to AlasdairM:
I am not so sure because the OP suggests that it is a reversal rather than a shift.
the compass would need to be warm or hot and to been subject to a overprinting field to hold a new signature.
we do this to rocks from time to time in the lab as part of tectonic plate reconstruction and its quite hard to see how a phone under normal temperatures could overprint a magnet and get a complete and accurate 180 change.
so the big question is: is it a true reversal or just a random change? (If so, Alasdair may have the correct answer)
I am not so sure because the OP suggests that it is a reversal rather than a shift.
the compass would need to be warm or hot and to been subject to a overprinting field to hold a new signature.
we do this to rocks from time to time in the lab as part of tectonic plate reconstruction and its quite hard to see how a phone under normal temperatures could overprint a magnet and get a complete and accurate 180 change.
so the big question is: is it a true reversal or just a random change? (If so, Alasdair may have the correct answer)
In reply to seaofdreams:
Photo (took a while to be processed by UKC, cos it's well dodgy >8-) http://www.ukclimbing.com/images/dbpage.php?id=161856
Apologies for delay folks. The reversals appeared to be complete (i.e. 180 deg.) and to be 'permanent' all-or-nothing events. Bringing my phone briefly in proximity to either compass deflects the needle severely, but doesn't cause a 'permanent' change. 'permanent' means it stays like that while in use on the hill or whereever, but may be re-polarised again. The 'permanent' polarity switches seemed to occur after the compass + phone were in the same pocket in my rucksack for some time, i.e. hours. Up to room temperature at most, and mostly much lower. Some magnets can be re-polarised by stroking them with another magnet, especially if the latter is a stronger one. Silva confirmed that mobile phones and other devices may re-polarise a magnetic compass. Could be another opportunity for the gear merchants - a phone pocket away from the main top pocket ? >8-)
Photo (took a while to be processed by UKC, cos it's well dodgy >8-) http://www.ukclimbing.com/images/dbpage.php?id=161856
Apologies for delay folks. The reversals appeared to be complete (i.e. 180 deg.) and to be 'permanent' all-or-nothing events. Bringing my phone briefly in proximity to either compass deflects the needle severely, but doesn't cause a 'permanent' change. 'permanent' means it stays like that while in use on the hill or whereever, but may be re-polarised again. The 'permanent' polarity switches seemed to occur after the compass + phone were in the same pocket in my rucksack for some time, i.e. hours. Up to room temperature at most, and mostly much lower. Some magnets can be re-polarised by stroking them with another magnet, especially if the latter is a stronger one. Silva confirmed that mobile phones and other devices may re-polarise a magnetic compass. Could be another opportunity for the gear merchants - a phone pocket away from the main top pocket ? >8-)
In reply to Roland Ascroft:
We get this a lot after storing our compasses in the official Silva storage case (holding 28 compasses). Then we wonder why groups get lost...
If you get another compass and wave them around each other for a while it seems to flip the broken one back again. If you are lucky.
We get this a lot after storing our compasses in the official Silva storage case (holding 28 compasses). Then we wonder why groups get lost...
If you get another compass and wave them around each other for a while it seems to flip the broken one back again. If you are lucky.
In reply to seaofdreams: Actually, if the needle is truly that (i.e., long and thin) as it is on my Silvas, then the shape anisotopy would essentially guarantee a 180 degree flip - or no flip at all. I still wonder about the mobile phone though ... but it got me thinking about ARM........
Strange....
Gary (trying to remember my Geomag days.....)
Strange....
Gary (trying to remember my Geomag days.....)
In reply to gdstorrick:
stupid one perhaps, but are you carrying it around you neck, and having a magnet attachment for your camelbak/hydration system thing?
that tends to repolarise compasses quite successfully.
stupid one perhaps, but are you carrying it around you neck, and having a magnet attachment for your camelbak/hydration system thing?
that tends to repolarise compasses quite successfully.
Hey-ho Silva! Silva (AKA Fiskars Outdoor) in Livingston re-polarised my compasses free of charge AND replaced the base-plate which was broken on one of them. Well impressed.
It's frightening to find how many magnetic fields there are in a house - not easy to find a safe place to store my magnetic compasses.
For anyone else needing the address:
Silva Ltd
7 Elphinstone Square
Deans Industrial Estate
Livingston
EH54 8RG
It's frightening to find how many magnetic fields there are in a house - not easy to find a safe place to store my magnetic compasses.
For anyone else needing the address:
Silva Ltd
7 Elphinstone Square
Deans Industrial Estate
Livingston
EH54 8RG
I had the same problem a few years ago. Had no idea how it happened and just assumed the compass was gubbed and bought a new one. Good to know it can be fixed and they do it for free! Thanks
In reply to seaofdreams:
So, when you were a kid, did you never magnetize a needle by stroking a magnet along it?
You don't need to need to muck about with heating, Curie points and all that stuff. For rocks, you might want to do that as a demonstration of how rocks might acquire a magnetic orientation (they are heated above the Curie point, destroying the magnetic orientation; as they cool, they take on the magnetic orientation of their current orientation wrt Earth's magnetic north).
http://en.wikipedia.org/wiki/Curie_temperature
Depending on the speaker technology used in the phone (piezo vs magnetic), there may be a fairly strong rare earth magnet for the speaker. Strong magnets mean smaller voice coils and lower drive currents, i.e. better efficiency). Easily checked: stick your phone into a pile of paper clips and see if it picks them up. Mine does (but I have to remove the plastic shell: an ancient Nokia "builder's phone").
> the compass would need to be warm or hot and to been subject to a overprinting field to hold a new signature.
So, when you were a kid, did you never magnetize a needle by stroking a magnet along it?
You don't need to need to muck about with heating, Curie points and all that stuff. For rocks, you might want to do that as a demonstration of how rocks might acquire a magnetic orientation (they are heated above the Curie point, destroying the magnetic orientation; as they cool, they take on the magnetic orientation of their current orientation wrt Earth's magnetic north).
http://en.wikipedia.org/wiki/Curie_temperature
Depending on the speaker technology used in the phone (piezo vs magnetic), there may be a fairly strong rare earth magnet for the speaker. Strong magnets mean smaller voice coils and lower drive currents, i.e. better efficiency). Easily checked: stick your phone into a pile of paper clips and see if it picks them up. Mine does (but I have to remove the plastic shell: an ancient Nokia "builder's phone").
In reply to captain paranoia:
> (In reply to seaofdreams)
>
> [...]
>
> So, when you were a kid, did you never magnetize a needle by stroking a magnet along it?
>
I was wondering about that too. My memories of science at junior school (as it was then called) are filled with experiements which involved floating magnetised needles in bowls of water. Is this stuff not taught anymore? >
> [...]
>
> So, when you were a kid, did you never magnetize a needle by stroking a magnet along it?
>
In reply to Roland Ascroft:
Flipping compass, sending me in the wrong direction again . . . !
Seriously though, I can only imagine it is some kind of random pocket of polarity reversal as discussed in the documentary entitled 2012 . . .
Flipping compass, sending me in the wrong direction again . . . !
Seriously though, I can only imagine it is some kind of random pocket of polarity reversal as discussed in the documentary entitled 2012 . . .
In reply to captain paranoia:
you are not giving something a field you are overprinting one that is there already.
you are not giving something a field you are overprinting one that is there already.
In reply to gdstorrick:
I agree if the needle is a single magnetic zone which I doubt it will be when its removed from the confines of the factory.
I agree if the needle is a single magnetic zone which I doubt it will be when its removed from the confines of the factory.
In reply to seaofdreams:
I'm always surprised when I hear about this causing navigation issues, unless you are in a white out or at night you should be able to tell instantly that the polarity has reversed when you compare your map to the landscape (and the position of the sun), then you just need to remember which end points north and off you go.
Of course it helps that I have a freaky ability to always know where north is to within a couple of degrees (yes even being spun round with a blindfold on)
I'm always surprised when I hear about this causing navigation issues, unless you are in a white out or at night you should be able to tell instantly that the polarity has reversed when you compare your map to the landscape (and the position of the sun), then you just need to remember which end points north and off you go.
Of course it helps that I have a freaky ability to always know where north is to within a couple of degrees (yes even being spun round with a blindfold on)
In reply to seaofdreams:
How is that relevant to your comment that heat is required (implying Curie point)?
If I take a needle, and stroke it with a magnet, I can create a magnetic alignment within the needle. I can reverse the magnet and repeat the procees, I can magnetize the needle the other way.
Heating something to the Curie point destroys the existing magnetic properties (it becomes paramagnetic). On cooling, it will adopt the local magnetic orientation. The wiki is quite helpful.
> you are not giving something a field you are overprinting one that is there already.
How is that relevant to your comment that heat is required (implying Curie point)?
If I take a needle, and stroke it with a magnet, I can create a magnetic alignment within the needle. I can reverse the magnet and repeat the procees, I can magnetize the needle the other way.
Heating something to the Curie point destroys the existing magnetic properties (it becomes paramagnetic). On cooling, it will adopt the local magnetic orientation. The wiki is quite helpful.
In reply to captain paranoia:
think about what you have jut written and consider all of my postings. the problem I am having with this whole idea is that the flip is not random and owing to the shape and make up of a needle in a compass it seems strange that you can flip accurately through 180 degrees a needle on a cold day by using a speaker from a phone.
I dont know the answer but I do know what my Post graduate education in rock magnetics in Toronto taught me and without reducing the intensity of its field in the compass I doubt to you could sustain permeant and accurate re polarisation (assuming the needle is not one dimension and not one magnetic zone).
furthermore if this were possible then every time to passed through a security tag remove in a shop you would overwrite the field in your compass.
this has nothing to do with the curie temperate of iron which I know is quite high (1043 K) and everything to do with the drop in magnetic susceptibility with an increase in temperature making the change easier. this change allows the overwriting effect of less powerful zones which would produce a random change in direction (assuming the needle is not one dimension and not one magnetic zone).
think about what you have jut written and consider all of my postings. the problem I am having with this whole idea is that the flip is not random and owing to the shape and make up of a needle in a compass it seems strange that you can flip accurately through 180 degrees a needle on a cold day by using a speaker from a phone.
I dont know the answer but I do know what my Post graduate education in rock magnetics in Toronto taught me and without reducing the intensity of its field in the compass I doubt to you could sustain permeant and accurate re polarisation (assuming the needle is not one dimension and not one magnetic zone).
furthermore if this were possible then every time to passed through a security tag remove in a shop you would overwrite the field in your compass.
this has nothing to do with the curie temperate of iron which I know is quite high (1043 K) and everything to do with the drop in magnetic susceptibility with an increase in temperature making the change easier. this change allows the overwriting effect of less powerful zones which would produce a random change in direction (assuming the needle is not one dimension and not one magnetic zone).
In reply to TimR:
not really - its more likely to be perfectly formed ifs its made well out of steel but the key to the problem is that as soon as you damage the lattice of the needle you introduce new zonation which interact with each other and changes the over all field slightly. this is why should never drop or hit a compass.
although I admit its not impossible to make a perfectly zoned needle it is highly unlikely and what is far more likely to happen is that the combination of many zones working together produces and over all N-S field. if the needle were perfectly one dimensional it would be impossible to have anything other than N or S running along the axis. if you change a few zones by running a magnetic over the needle to get a change in only the zones which are susceptible at the temperature to that magnetic field. an over all change will occur but it will be small until you reach a tipping point where the needle flips but it is highly unlikely to be accurate unless to completely removed the original filed
the earth is a good example of roughly what i am on about. every now and again it roughly repolarise because the overall change tends toward the different direction and tipping point occurs. but the poles never line up with the spin axis (hence declination) and change constantly (which is affected my many factors). the key to my point is that the change is rough and random (not accurate).
I may suggest that what we are seeing is the OP thinking the change is accurate when its not (cloud be close and the error in a reading for most people is +- 3 deg)
not really - its more likely to be perfectly formed ifs its made well out of steel but the key to the problem is that as soon as you damage the lattice of the needle you introduce new zonation which interact with each other and changes the over all field slightly. this is why should never drop or hit a compass.
although I admit its not impossible to make a perfectly zoned needle it is highly unlikely and what is far more likely to happen is that the combination of many zones working together produces and over all N-S field. if the needle were perfectly one dimensional it would be impossible to have anything other than N or S running along the axis. if you change a few zones by running a magnetic over the needle to get a change in only the zones which are susceptible at the temperature to that magnetic field. an over all change will occur but it will be small until you reach a tipping point where the needle flips but it is highly unlikely to be accurate unless to completely removed the original filed
the earth is a good example of roughly what i am on about. every now and again it roughly repolarise because the overall change tends toward the different direction and tipping point occurs. but the poles never line up with the spin axis (hence declination) and change constantly (which is affected my many factors). the key to my point is that the change is rough and random (not accurate).
I may suggest that what we are seeing is the OP thinking the change is accurate when its not (cloud be close and the error in a reading for most people is +- 3 deg)
In reply to Roland Ascroft: ahh spelling errors sorry i am tired
In reply to Roland Ascroft:
Had this happen a few times over the years with various compasses. Just sorted it out with a magnet rather than sending it back to Silva.
Had this happen a few times over the years with various compasses. Just sorted it out with a magnet rather than sending it back to Silva.
In reply to seaofdreams:
Nothing strange about it. It would be more difficult not end up with the magnetism aligned along the axis of the needle. The geometry of the needle and the fact that it is free to pivot almost guarantee it!
> (In reply to captain paranoia)
>
> think about what you have jut written and consider all of my postings. the problem I am having with this whole idea is that the flip is not random and owing to the shape and make up of a needle in a compass it seems strange that you can flip accurately through 180 degrees a needle on a cold day by using a speaker from a phone.
>
> think about what you have jut written and consider all of my postings. the problem I am having with this whole idea is that the flip is not random and owing to the shape and make up of a needle in a compass it seems strange that you can flip accurately through 180 degrees a needle on a cold day by using a speaker from a phone.
Nothing strange about it. It would be more difficult not end up with the magnetism aligned along the axis of the needle. The geometry of the needle and the fact that it is free to pivot almost guarantee it!
In reply to Hairy Pete:
errr no - sorry. it would be close but not accurate
last time then I quit - consider a theoretical one dimensional needle with 5 zones
we shall assume that the magnetic field of the earth is 180 deg for this description (near enough south geographic pole)
the north point of the needle would point to 0 degrees if the sum of all 5 zones equates to 0 degrees. if we change the magnitude or direction of one of the zones by say dropping the compass then the over all field has changed. because in our example the needle only has one dimension these changes can only be 180 degree flips so the perceived direction does not change but the magnitude does (5 working in harmony compared with 4 vs 1)
the problem is that the real needle is 3 dimensional allowing for a slight change to orientation before a flip occurs. this is a factor of the random alignment of zones within the medium (ie all zones are not lined up with the long axis of the needle)
I am done - good night
errr no - sorry. it would be close but not accurate
last time then I quit - consider a theoretical one dimensional needle with 5 zones
we shall assume that the magnetic field of the earth is 180 deg for this description (near enough south geographic pole)
the north point of the needle would point to 0 degrees if the sum of all 5 zones equates to 0 degrees. if we change the magnitude or direction of one of the zones by say dropping the compass then the over all field has changed. because in our example the needle only has one dimension these changes can only be 180 degree flips so the perceived direction does not change but the magnitude does (5 working in harmony compared with 4 vs 1)
the problem is that the real needle is 3 dimensional allowing for a slight change to orientation before a flip occurs. this is a factor of the random alignment of zones within the medium (ie all zones are not lined up with the long axis of the needle)
I am done - good night
In reply to seaofdreams:
You need to consider what's actually happening in the real world. How did Silva magnetise and manufacture the needle in the first place? I've had a needle flip. Took it back to the shop, they changed it, no problem and said it was always happening.
You need to consider what's actually happening in the real world. How did Silva magnetise and manufacture the needle in the first place? I've had a needle flip. Took it back to the shop, they changed it, no problem and said it was always happening.
In reply to seaofdreams:
What is not accurate? I think you will find that the geometry of the needle is largest factor in determining how closely it aligns itself with the magnetic field (give or take 180 degrees).
No consideration necessary. Magnetic zones may be applicable to rocks but not (in a practical context) to solid iron/steel. The permeability of steel is such that if you have enough magnetic force to magnetise any part of the material then the rest of the specimin will follow, wiping out any "zones" (generally speaking. - I'm sure it's possible to contrive situations which show otherwise).
Returning to alignment issue: if I had a perfectly balanced needle, on a perfectly friction free pivot, no draughts etc., and NOT magnetised, which direction would it point?
> (In reply to Hairy Pete)
>
> errr no - sorry. it would be close but not accurate
>
> errr no - sorry. it would be close but not accurate
What is not accurate? I think you will find that the geometry of the needle is largest factor in determining how closely it aligns itself with the magnetic field (give or take 180 degrees).
>
> last time then I quit - consider a theoretical one dimensional needle with 5 zones
> last time then I quit - consider a theoretical one dimensional needle with 5 zones
No consideration necessary. Magnetic zones may be applicable to rocks but not (in a practical context) to solid iron/steel. The permeability of steel is such that if you have enough magnetic force to magnetise any part of the material then the rest of the specimin will follow, wiping out any "zones" (generally speaking. - I'm sure it's possible to contrive situations which show otherwise).
Returning to alignment issue: if I had a perfectly balanced needle, on a perfectly friction free pivot, no draughts etc., and NOT magnetised, which direction would it point?
In reply to Hairy Pete: I actually have car compass which is re-polarized, but I got it from the market and just didn't notice untill I got it home and put it in the car, You just have to remember you are going South you are actually going north, probably not as critical in a car compass as in a Silva.
In reply to Roland Ascroft: One of my compasses flipped 180 degrees after I left it in the car for a couple of weeks. Didn't notice until I was on the top of a hill in the clag. I've occasionally got lost in the past due to thinking I know better than the compass, but this time I actually did!
Another compass seems to have re-magnetised itself randomly, and points ESE or something (found this out in the middle of Knoydart). This seems a bit harder to understand than the polarity being reversed.
Another compass seems to have re-magnetised itself randomly, and points ESE or something (found this out in the middle of Knoydart). This seems a bit harder to understand than the polarity being reversed.
In reply to seaofdreams:
That has been a problem in some outdoor shops, where staff don't know to keep compasses away from magnetic security devices. Result: lots of returns of faulty compasses...
I guess the thing to take away from this thread is that rocks and freely-pivoting metal compass needles, which are essentially one-dimensional and a single magnetic zone, behave differently.
Incidentally, I see that the Leonard de Vries book of Experiments is available online as a PDF:
http://www.arvindguptatoys.com/arvindgupta/bookofexpts.pdf
> furthermore if this were possible then every time to passed through a security tag remove in a shop you would overwrite the field in your compass.
That has been a problem in some outdoor shops, where staff don't know to keep compasses away from magnetic security devices. Result: lots of returns of faulty compasses...
I guess the thing to take away from this thread is that rocks and freely-pivoting metal compass needles, which are essentially one-dimensional and a single magnetic zone, behave differently.
Incidentally, I see that the Leonard de Vries book of Experiments is available online as a PDF:
http://www.arvindguptatoys.com/arvindgupta/bookofexpts.pdf
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