AC magnetic field strengths
dkelvey at hotmail.com
Fri Mar 17 14:17:47 CDT 2017
You should also measure at about 1 inch. It is an inverse square decrease
with distance. The rate of drop off is related to the starting point and the
shape of the field.
Some have a flat field out to some distance before they start the inverse square
From: cctalk <cctalk-bounces at classiccmp.org> on behalf of js--- via cctalk <cctalk at classiccmp.org>
Sent: Thursday, March 16, 2017 5:06:09 PM
To: General at classiccmp.org; Discussion@
Subject: Re: AC magnetic field strengths
That is in fact how I spot degauss CRT screens, but using a flat wood
boring bit (metal, obviously, instead of a paint stick) with the magnet
stuck on the end, spun around with a drill.
On 3/16/2017 6:37 PM, dwight via cctalk wrote:
> It sounds like one can make a fine tape degausser by connecting
> a super magnet to the end of a paint stirring rod and use a drill
> to spin it.
> From: cctalk<cctalk-bounces at classiccmp.org> on behalf of Tapley, Mark via cctalk<cctalk at classiccmp.org>
> Sent: Wednesday, March 15, 2017 11:51:07 AM
> To: General Discussion: On-Topic and Off-Topic Posts
> Subject: Re: AC magnetic field strengths
> On Mar 15, 2017, at 12:01 PM, Al Kossow via cctalk<cctalk at classiccmp.org> wrote:
>> I bought an AlphaLabs GM-2 Gaussmeter for another project, and measured the AC magnetic
>> field strength touching these devices yesterday, since I really didn't have any idea beyond
>> order of magnitude what they might be
>> Handheld tape head demagnetizer: 40 Gauss
>> GC Elec 9317 CRT degausing coil: 70 Gauss
>> Audiolab TD-3 desktop bulk eraser: 1000 Gauss
>> Inmac 7180 or
>> RS 44-233A handheld bulk tape erasers: 2000 Gauss
>> also the DC field of a 1/4" button super magnet like on the
>> backs of clip on badges is about 3000 Gauss
> More context available at:
> ranging from 50 femtoGauss (what the Gravity Probe B SQUID magnetometers measured with several days’ averaging) to 100 MegaGauss (strongest pulsed field ever obtained at Sandia Labs).
> Interestingly that page claims 12.5 kGauss for a "neodymium–iron–boron (Nd2 Fe14 B) rare earth magnet” (subscripts on the atomic symbols got converted to plain text during cut-n-paste). Guess the badges have weaker versions?
> Interesting to compare earth field and the badge fastener field to practical exposure limit for pacemakers - only about a factor of 10 at the poles - and to loudspeaker coils, which are 5000 times above the recommended pacemaker limit.
> Now I know why people with pacemakers don’t like rock music (and name tags)!
> - Mark
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