AC magnetic field strengths

dwight dkelvey at
Thu Mar 16 18:37:32 CDT 2017

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> on behalf of Tapley, Mark via cctalk <cctalk at>
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> 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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