In article ,
Joseph Gwinn wrote:

In article ,
Don Foreman wrote:

First results are quite encouraging. I was told by the helpful folks
at Boston Scientific that 1 gauss is an acceptable level of field
strength for 60 Hz fields. I don't know if that's RMS or peak to zero,
doubt if it's that precise. Being medical and actually in print, it's
probably quite conservative.

It's probably RMS, but the standards they are meeting will say. The
decision to fire will require the condition to endure for something like
ten seconds before anything happens, to cut down on false alarms.

I'm not sure what the frequency of peak sensitivity is, or if 60 Hz is
anywhere near. As I understand it, what triggers the shock is detection
of fibrillation, whose signal is lots of random "high frequency" noise
combined with no heartbeat pulse. The details are probably best
documented in patents and articles in medical journals. Perhaps the
engineering fellows can suggest which patents and articles to read.

A google search on the names of the various fellows may also be
productive.

I did a little looking. One useful item is this:
http://www.spectrum.ieee.org/nov08/6921/3.

There are lots of patents from Medtronic: 5,464,430; 5,330,508; et al.

Haven't found anything on Boston Scientific, but haven't looked either.

Joe Gwinn


I did two experiments with MIG today. Machine is a Millermatic 210. I
had it set at where it seems to run well on 1/8" mild steel which is
what I mostly MIG. Settings were 3 on voltage knob, 50 on wirespeed.
I'll have Mary read an ampclamp tomorrow while I'm welding, but
current is whatever it is. I'd guess about 150 amps.

Cables were dressed fairly carefully. The sensor was clipped to my
shirt near my left shoulder. I welded in normal position at normal
distance, which is with my chest maybe 18" from the puddle.

On the first run the peak value recorded was about 1 gauss. I moved
the groundclamp to within 6" of the weld zone. Then the peak value
recorded was about 0.38 gauss.

It strikes me that one can turn this around: Using that magnetic field
sensor as the core, make a high-field warning device that beeps loudly
when threshold is exceeded. The patents and articles can inform the
design of the trigger circuit, so the warning device has the same
sensitivity profile as the real ICD, but with enough margin to allow one
to avoid triggering the ICD by accident.


Joe Gwinn