First findings on magnetic field while welding

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.
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.
This setup (or lower current for thinner metal) would do about 90% of what I do with MIG. I have welded heavier stuff, but not often. Now I'll get help if/when I need thicker stuff done.
I hope things go as well with TIG. I'll be trying that tomorrow.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Don, I think you need to know what the susceptability of the device is to electromagnetic interference to make your tests meaningful. There is a very good chance that the manufacturer has made these tests for "CE" certification. I would recommend contacting the manufacturer for this number. There is an ISO test that these devices must pass for this certification. The results of this test is PASS or FAIL, so it would be nice to know what that test limit is. Personally, I would think that 10 gauss or more is a non-issue, especially at such low frequencies that you are concerned with. EMF caused malfunctions normally occur at much higher frequencies. Steve

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 17 Jan 2009 10:08:01 +0100, "Steve Lusardi"

Indeed! I have data from Boston Scientific: "suggested guidelines for limiting peak exposure to power freqency and static fields" that suggests static B field be limited to 10 gauss or less, 60Hz B field to 1 gauss or less. After the expected disclaimers, it notes that "no published documentation of pacemaker or defibrillator interference at those levels [has been] found [to date]." A footnote cites the EPRI reference.
I think these guidlines are probably quite conservative.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Joseph Gwinn wrote:

That's a good idea, make a EMF data logger to keep on you when welding so that in the event you do get a bogus mule kick you can review the data and determine the conditions when it occurred to avoid them in the future.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 17 Jan 2009 11:35:57 -0500, Joseph Gwinn
<snip>

This stuff is a bit over my head and interest... but I can poke around the patent site pretty well. The following long link my be of some interest:
http://patft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.htm&r=0&p=1&f=S&lP&Query l%2F607%2F4&d=PTXTg
The key to finding stuff of interest is to search via Classifications. The link above is just a simple search on Class 607/4. Which translates to:
US Patent Class 607:
SURGERY: LIGHT, THERMAL, AND ELECTRICAL APPLICATION
1 LIGHT, THERMAL, AND ELECTRICAL APPLICATION 2 .~ Electrical therapeutic systems 3 .~.~ Combined with nonelectrical therapy 4 .~.~ Combined cardioverting/defibrillating and pacing 5 .~.~ Cardioverting/defibrillating 6 .~.~.~ Sensing body condition or signal other than electrocardiographic signal 7 .~.~.~ Controlling or indicating stimulation level 8 .~.~.~ Computing energy required or contact impedance 9 .~.~ Heart rate regulating (e.g., pacing) 10 .~.~.~ With nonimplanted generator 11 .~.~.~ Regulating or compensating stimulus level 12 .~.~.~ Stimulation raised above energy source level 13 .~.~.~ Reducing output recovery time 14 .~.~.~ Treating or preventing abnormally high heart rate
and so on...
The easiest way to find stuff is by looking at the classes of other devices like you want to find more of.
Not knowing exactly what my be of help to/for Don I can't do much more. He may be able to peruse the above link and find items of interest to read up on.
Google patent interface is a lot more user friendly once you narrow things down a bit. Using the patent suggested by Joseph, a simple Google patent search would look like this:
http://www.google.com/patents?q=5,464,430&btnG=Search+Patents&num
--
Leon Fisk
Grand Rapids MI/Zone 5b
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 16 Jan 2009 22:30:33 -0600, Don Foreman
I didn't get to TIG today. I'll do that tomorrow. Today I did more MIG tests. I was surprised at how low the fields were. My findings indicate that anything within the capacity of the machine (Millermatic 210) will be well below the 1 gauss guidline, given careful dressing of cables -- torch lead and ground cable.
My test coupon started out as 1/8" steel but it's over an inch thick now!
I got to doubting the sensor so I did a calibration sanity check of sorts. I wound a coil, 15 turns of 18-gage magnet wire, 1.8" ID, 2" OK, .22" wide. When I modelled that in a magnetic fields FEA program I found that 1 amp would produce 3.6 gauss in the center of the coil. The sensor, place in the center of the coil, read 3.5 gauss; definitely close enough for this exercise.
I'm really glad I bothered to do this testing to drill a little deeper than the one-size-fits-all guidance of "not recommended".
I'll still be a bit antsy about welding at first, but things do look promising.
We'll see about TIG. Current levels are similar so the results may be too. I hope. We'll see. The HF could present an E-field issue but that's easily managed with Faraday shielding. The E-field spec is 1 kilovolt per meter.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Don Foreman wrote:

(...)
Excellent news, Don!
Have you discovered arrangements of cables, settings of the welder, position of body, etc. that result in unacceptably high field strength?
I'd be leery of HF coupling which might be particularly harmful and perhaps outside the passband of your sensor. As a first-order test it might be educational to record a detuned A.M. radio while welding and see if those steep step functions result in potentially nasty harmonics in the electrical domain.
--Winston
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Well no, but I've no doubt that such arrangements exist. I was careful to arrange cables to *minimize* field strength. I then used body positions and welder settings that I normally use while welding.

I'm not too concerned about that. Shielding is effective at RF frequencies, and the inputs of cardiac devices are subjected to both low-level analog filtering and then digital filtering. 60Hz magnetic fields are of concern because of their possible magnitudes with >100 amps flowing, and because they are much closer to the passband of the ICD's.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Don Foreman wrote:

If you discover that you cannot generate a field anywhere near the guideline even with cable dress that *looks* like it would be dangerous to an ICD user, that would be useful info for you, post-op. You need to discover what kinds of arrangements and settings you'll need to avoid, post-op, if any.
Maybe that 'common mode' mitigation is as important as you and I think it is. Perhaps not. Post-op is not the time to uncover the critical variable.
You've seen the FCC EMI passband charts, I'm sure. Clearly there must be an equivalent susceptibility chart for the ICD in question. 'Static field' and '60 Hz' field strengths are useful info but it would be much more useful for you to know the field strengths that could be troublesome for all the other frequencies as well.
:)
--Winston
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Chain mail welding jacket?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 16 Jan 2009 22:30:33 -0600, Don Foreman
Don, maybe this will show a lack of understanding of magnetism on my part, but couldn't you put a metallic shield of some sort over your clothing between you and the pacer and leads and create a Gaussian shield of sorts?
RWL
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 18 Jan 2009 11:57:37 -0500, GeoLane at PTD dot NET <GeoLane at PTD dot NET> wrote:

Shielding against low-frequency magnetic fields is impractical, but a metallic shield could indeed protect against E-fields as from HF.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 19 Jan 2009 00:14:28 -0600, Don Foreman

I'd have thought that meat was a reasonable E-field screen :-)
Mark Rand RTFM
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 19 Jan 2009 09:55:42 +0000, Mark Rand

It is.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Keywords:

I suspect you could do an OK job if you replaced the metal plates in an old style flak jacket with mu metal, but it sounds like you are good to go without that sort of heroics.
Don, I have a roll of thin (15 mil?) mu metal in my junk box. I haven't fished it out in years, but I suspect I've got about a square foot (or more) of the stuff. I have no idea how helpful it might be, or if it has been damaged and has lost some of its effectiveness. It has to be at least 30 (probably more like 40) years old. If you want it, it's yours. With your measuring widget, you could even test and see if it helps at all.
Doug White
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 19 Jan 2009 15:53:18 GMT, snipped-for-privacy@alum.mit.edu (Doug White) wrote:

Thanks, Doug, that's very generous of you. I'll decline but I do appreciate the offer. Mu-metal must be hydrogen annealed after any shaping in order to retain its properties. In any event, I don't seem to have a B-field issue in my particular setup and situation.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 16 Jan 2009 22:30:33 -0600, Don Foreman

Update: TIG looks good to go. I'm grinnin'.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 19 Jan 2009 00:02:15 -0600, Don Foreman

Ill bet there is a paper...and a government grant in your research.
<G>
Gunner
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.