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Calibration of Magnets


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Bhavin Raval

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Posted 01 February 2011 - 05:29 AM

Dear All,

In my company we are having magnets before the packing of final proudcts on some of the lines. I would like to know how magnets can be calibrated?

Thanks in advance.

Regards,

Bhavin



GMO

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Posted 01 February 2011 - 07:18 AM

Are they CCPs? Personally I never agree with magnets being CCPs because they vary in strength according to distance and also have a nasty habit of dumping the contaminants back into the product. Also magnets will only be effective on iron and low grade stainless steel. Most food factories have high grade stainless so what's the point? So I would ask, why do you have it before you consider getting it calibrated.



Foodworker

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Posted 01 February 2011 - 09:40 AM

It is possible to find companies that will calibrate magnets, but they are few and far between. Some companies can indirectly calibrate electromagnets but the permanent rare earth type are more difficult.

Magnets have their uses in some sectors - tea, herbs/spices etc, but are seldom true CCPs.

One of the problems that you will find in calibration of magnets is setting an acceptable tolerance limit. There are other factors related to how you use the magnet which have a greater influence on their efficiency eg distance, positioning, monitoring of pick up, cleaning of their surfaces.

A fairly common system is to trend the strength rather than calibrate it. When purchased they should have a nominal strength in Tesla, periodic checking is done and when the strength has dropped by 10% they are changed.

GMOs point about dumping ferrous dust is very valid. If they are not checked or cleaned there comes a point where the weight/shape of the dust exceeds the pull of the magnets and a great lump falls off into the product.



Biss

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Posted 01 February 2011 - 10:55 AM

Hi,

I think it is better to calibrate the magnet through external agency. You can find an external agnecy near to your place.
NPL can do the calibration but its very costly. Or you can buy a gauss meter and do the calibration but again gauss meter needs to be calibrated from external lab. Also its not easy get a good gauss meter, we have one imported from Japan


Biss

cosmo

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Posted 07 February 2011 - 09:29 PM

I tend to think that magnets are great for reducing tramp metal in the process and protecting machines, but the CCP should be metal detection as it is detecting not trapping.
In regards to the strength it is surprising the actual weight a rare earth magnet can hold. The most simplistic form of calibration I have seen was 5 & 10kg scale calaibration weights being attached to the magnet. If it held it passed, if the weight dropped the magnet was replaced. (This was done from new and the max single weight held was recorded and showed a loss of strength over time)
The simplistic logic was that if it held a heavy static weight it would capture a lighter weight passing over it at velocity. I dont know if they did the actual calculation or tested the theory, but I did see a current HACCP certificate.



Charles.C

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Posted 07 February 2011 - 10:07 PM

Dear cosmo,

What is tramp metal ??

Rgds / Charles.C


Kind Regards,

 

Charles.C


cocoabeanny

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Posted 14 February 2011 - 09:42 AM

Hello,

we monitor our CCP and oPRP permanent magnets with a gaussmeter every month. The gaussmeter itself is send for calibration every year. The actual test is not complicated, it is done by our electicians and if the value drops below a defined strengh the magnet bar gets exchanged. The gaussmeter we have I think is from Goudsmith.

regards Beanny



cosmo

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Posted 15 February 2011 - 09:15 PM

Dear cosmo,

What is tramp metal ??

Rgds / Charles.C



Dear Charles,
Tramp metal is a term used for metal scrapings/ shavings that seem to appear occasionally and originate from within the process machinery. (nuts and bolts excluded). I guess it could be a local expression.
Cosmo





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