Degaussing/demagnetising my Trident hasn't worked!

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Re: Degaussing/demagnetising my Trident hasn't worked!

Post by richtel »

There are a couple of reasons why I don't like Lepsi. One is that most phones often have powerful magnets in them so waving your watch over them might perversely come come with a little risk, but also the app doesn't tell you enough.

When a watch is magnetised, components within become 'permanent' magnets with a distinct polar difference- if you remember the bar magnets with a North and South end. If you were to use a compass (which is itself a small suspended bar magnet) and move a magnetised watch towards it, the needle will deflect. It'll also deflect if you bring a big lump of non-magnetised iron towards it but the difference is that if you were to rotate your magnetised watch or magnetised lump of iron and brought it towards the compass again, the needle would deflect...the other way. Therefore you can tell with the compass when you have a magnet close, or if it is just a lump of ferrous material. The magnetometer in your phone, and the Lepsi app, wouldn't show you that difference.

It could be that what you're seeing with Lepsi is just that you're holding something ferrous over the sensor, magnetic or not. Indeed I've just tried holding an unmagnetised tin lid against my compass which shows little effect with the needle being mildly attracted to the lid from any orientation, but has a strong indication with Lepsi.

Most watches don't contain materials that easily magnetise- stainless steel is hard to magnetise, and brass in the movement is amagnetic of course. It's mostly the springy-steel hairspring which might be affected. A soft iron core around the movement is possible to magnetise, but because it surrounds the movement, little magnetic flux will go through the movement to affect it. The only way you're likely to demagnetise anything like that is to surround the device with extremely strong magnetic field- such as one of the degaussers which totally surrounds the device. But as mentioned above, it's probably not worth it because it's unlikely to be affecting the movement.

The effect that you see with the watch being attracted to the face of the demagnetiser will simply be due to the demagnetiser acting like an electromagnet and attracting the ferrous soft iron in the watch, and if the movement really is magnetised, then I'm afraid your demag wouldn't really cut it- the movement would need to be de-cased or the iron core removed from around it.
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Re: Degaussing/demagnetising my Trident hasn't worked!

Post by iain »

Thank you Rich, that is a very helpful and informative response. Much appreciated.
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