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Demagnetizing digital caliper?

without damaging it?

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Frank.N Storm15/11/2012 22:48:07
49 forum posts
1 photos

Hi gents, new hear, so allow a question.

My good digital caliper got magnetized, really bad must always clean the swaff.

Can I demagnetize it or does that destroy the electronieks?

Thanks, Frank

Stub Mandrel16/11/2012 20:47:29
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4315 forum posts
291 photos
1 articles

Hi Frank,

It should not do any harm, they normally work by capacitance, not magnetism, but you could slide the reading head off and just demagnetise the metal bits.

Neil

Paul Boscott16/11/2012 21:06:43
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99 forum posts
21 photos

I foolishly measured a strong magnet and mine was attracting everything I hooked up a coil through an AC Variable Transformers It de magnetised it and it still works OK

Paul

Andyf17/11/2012 00:06:01
392 forum posts

If you have one of those Weller pistol-type soldering irons, that will demagnetise items which fit through the hairpin-shaped bit. Pass them through, but don't release the trigger until they are a foot or so away.

Might not work too well for digital calipers, though. The plastic parts wouldn't take kindly to contact with the hot soldering iron.

Andy

Ian S C17/11/2012 06:57:41
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7468 forum posts
230 photos

I have a demagnetizer that I made from a coil removed from the transformef from a Micro Wave oven, can't remember if it was the primary, or secondary, either will do. I use a transformer that used to run an electric blanket, think it is 6V, 9V, 12V, it works ok without overheating. Find the biggest transformer you can, the hole is bigger, thats the reason. Mine is in a plywood box, with a hole through where the core was also lined with ply. Ian S C

Ian P17/11/2012 09:04:07
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2578 forum posts
114 photos

As Neil said these operate using a capacitive sensor method and it is totally unaffected by magnetism. I don't bother removing the batteries and it seems not to make a difference if it is switched on or not. (The caliper that is, as the demagnetiser does ideally need to be operating!

One of the old central heating pumps that have a flat SS diaphragm as non magnetic interface between the windings and the impeller idea as a bench demagnetiser, (they overheat if left switched on for too long)

Ian

Andyf17/11/2012 09:20:51
392 forum posts

Do you put a lamp or something in series to limit the current, Ian?

Here's a trick with a transformer LINK

Whatever method is used, the object being degaussed needs to be removed slowly out of range while the demagnetiser is still running. If the object is nearby when the current is switched off, it will remain magnetised (perhaps more strongly than before).

I have also heard of magnets being attached to a piece of wood North-South-North-South and rotated in the lathe to produce an alternating field.

Andy

Ian P17/11/2012 09:39:57
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2578 forum posts
114 photos

Andy

My mention of overheating was just precautionary really, 'too long' is several hours.

I left mine on overnight and the workshop did take on a new aroma but no damage was done.

A series resistor would limit the current but then there is the problem of where to house and wire it. My demagnetiser took me all of 30 minutes to make and unlike the example you linked to can be used with any sized object. In theory I could use it upside down on the milling machine table if that needed degaussing.

Ian

Douglas Johnston17/11/2012 10:16:04
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767 forum posts
34 photos

An old ac motor with the rotor removed works well as a demagnetizer. Don't plug it into the mains, which would overload it, but connect the field winding to a 12/24V ac supply from a transformer.

Doug

Andyf17/11/2012 10:46:42
392 forum posts

Ian, my link leads to half way down the relevant page. Scroll up; tThe first post in the topic is the one I was meaning, where the E shaped laminations of the core are reassembled so they all point the same way, and the I sections discarded, or put in the box labelled Misc Shims. Like your version,the size of object isn't limited by having to pass through an aperture. In fact, it looks rather similar to an "official" Eclipse degausser.

All I need is a decent size scrap transformer, but those are getting harder to find since switched mode supplies have largely taken over.

Andy

Frank.N Storm17/11/2012 12:56:26
49 forum posts
1 photos

Many thanks, gents. Lots of good proposals here, im glad to here demagnetising doesnt damage the caliper. Beleive I have a coil or motor stator around somewhere; maybe big enough to put the caliper in.

Regards, Frank

Stub Mandrel17/11/2012 19:44:29
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4315 forum posts
291 photos
1 articles

My dad used to have a TV demagnetiser, just a 6 or 7" diameter coil in a paxolin former. It had a push button, plug into mains and move around the screen, then retreat about six feet and release button. This was from the days when TVs had valves and the early days of colour - he used to have a TV rental business in the 70s / 80s.

I once had a TV that had a bad colour patch in one corner. I fixed it by holding a loudpeaker magnet nearby and shaking it violently while moving it slowly away. It took three or four tries, but it worked.

Neil

Andyf17/11/2012 20:26:04
392 forum posts

Hi Neil,

I think most CRT TVs (I still use one in the bedroom, with a set top box) and CRT monitors have a degaussing coil around the front of the tube. Though that would give a pretty big aperture to pass things through, I don't know if it produces a strong enough field or indeed whether it could be detached in one piece when I finally go all modern and get a digital TV..

There's a (slightly) interesting short video here showing the principal of demagnetising a CRT using permanent magnets rotated in an electric drill; your method, but motorised..

Andy

Roger Woollett18/11/2012 12:09:50
133 forum posts
4 photos

Brilliant! I magnetised my caliper by foolishly measuring a magnet. I have been meaning to fix it for ages. As it happens I had an old central heating pump which worked just as Ian describes.

Roger Woollett

Ian Abbott18/11/2012 15:55:44
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279 forum posts
21 photos

On my first day as an apprentice, I was in the tool store and someone came up to the counter, slapped a hammer down and said, "Demagnetise that."

'Ah,' I thought, 'you're not going to fool me with that one...'

Ian

Stub Mandrel18/11/2012 17:02:37
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4315 forum posts
291 photos
1 articles

The degaussing coils on old TV's are pretty puny, they are also designed to give a 'pulse' of alternating magnetic field to something inside them. It is the degauss coil that makes the thump at switch on. Hence the need for something with a bit more welly when teh TV is badly magnetised,

I'm surprised the phyusical manget waving can demagnetise a tool - i thought the field would be too small.

Neil

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