I'm not sure I follow Mr. Owsley's message 100%, but there are a couple of fallacious assumptions if I follow it correctly.
In turn: The idea that a piece of medical equipment qualified to an emission limit (with or without margin) to be met at three or ten meters is supposed to automatically not interfere with an antenna that could be much closer to it than three meters. As Mr. Woodgate pointed out earlier in this thread, if you put things closer together than the separation distance at which they were qualified, all bets are off. Now the antenna will be on the outside of the largely metal ambulance, and the medical equipment inside, but there is no way to accurately account for that, except a real EMC test. More on that in a moment. The idea that because the medical equipment was qualified to 1, 3 or 10 V/m per EN61000-4-3 and 1000-4-6 (with or without margin), it should automatically be immune to rf transmissions originating from an antenna mounted on the ambulance. The degree of compatibility depends on the characteristics of the transmit antenna, how much power is dumped into it, and how much radiation leaks into the ambulance interior and even what resonance effects are going on in there. Again, the only way to check compatibility is a real EMC test. Real meaning that although CISPR emissions and IEC immunity requirements are colloquially termed EMC limits and requirements, they are in fact EMI limits and requirements, which are levied to increase the probability of overall EMC between the units which make up the integrated system, in this case an ambulance. In the general case of commercial EMI testing, the qualification test is the final EMC-related activity - there is no higher level of testing. But when you put together a moving platform, you had better check that everything plays well together, so the scenario envisioned by Mr. Owsley would be caught during the EMC test, not during actual use. Note that the EMI requirements levied on equipment that is designed to go in moving platforms, whether commercial or military, are based on different separation and different installations entirely. The antenna - EUT separation is one meter and the equipment is typically placed on a metallic ground plane, which simulates the platform installation. From: Bill Owsley <[email protected]> List-Post: [email protected] Date: Wed, 27 Jun 2007 19:10:43 -0700 (PDT) To: "Grasso, Charles" <[email protected]>, "Conway, Patrick R \(Houston\)" <[email protected]>, "Garnier, David S \(GE Healthcare\)" <[email protected]>, [email protected], [email protected] Subject: RE: Internal Margins for Emissions Testing Fits right in to when I was an EMT. I get called to see one you because of your chest pains and after hooking up the 12 lead heart monitor and finding evidence of an ongoing heart attack, I turn on the radio to setup communications with the hospital and find it blocked, and when I key the mike to check, it messes up the heart traces really bad too. No problem, in a few minutes - one less opinion in the margin discussion. Okay, so it wasn't one of you, at least not one I knew, but a brief time it was a very impressive opinion. "Grasso, Charles" <[email protected]> wrote: Without getting too much off the point: My wife works as an ICU nurse and I can tell you that the available functionality available on those products (i.e the software) trumps any amount of emissions margin everytime!! Best Regards Charles Grasso Compliance Engineer Echostar Communications Corp. Tel: 303-706-5467 Fax: 303-799-6222 Cell: 303-204-2974 Pager/Short Message: [email protected] Email: [email protected] From: [email protected] [mailto:[email protected]] On Behalf Of Conway, Patrick R (Houston) Sent: Wednesday, June 27, 2007 1:31 PM To: Garnier, David S (GE Healthcare); [email protected]; [email protected] Subject: RE: Internal Margins for Emissions Testing Interesting point... - I guess engineers in the medical field have an real good answer to the question "why do we need margin?" Best Regards, Patrick. [email protected] From: [email protected] [mailto:[email protected]] On Behalf Of Garnier, David S (GE Healthcare) Sent: Wednesday, June 27, 2007 1:00 PM To: [email protected]; [email protected] Subject: RE: Internal Margins for Emissions Testing Bob, Amen Brother! Regards, Dave Garnier PS: In an ICU room you can have many pieces of medical electronics connected to the patient, all of these devices may meet their repective requirements under 60601-1-2 and 2-x sub-requirements but still interfere with each other. Having said that, there are some imaging or monitoring technologies that have difficulties playing nicely with each other. Gentlemen, when you see your loved one go under a product you cert'ed and audited over the years, you gain a whole different perspective of your job! Regards, Dave Garnier David Garnier e GE HealthCare ___________________________________________ David S. Garnier Quality Assurance Technician Quality-DI RA-EMC 3000 N. Grandview Ave - M/S W-1250 Waukesha, Wi. 53188 Tel: 262.312.7246 Cel: 414.899.7580 From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Wednesday, June 27, 2007 11:17 AM To: [email protected] Subject: Fw: Internal Margins for Emissions Testing John, I agree...............but not if I'm laying on a table in an operating room : ) Bob Heller 3M EMC Laboratory, 76-1-01 St. Paul, MN 55107-1208 Tel: 651- 778-6336 Fax: 651-778-6252 ======================================================================== ==== John Woodgate o.uk> To Sent by: [email protected] [email protected] cc Subject 06/27/2007 10:40 Re: Internal Margins for Emissions AM Testing In message <[email protected]>, dated Wed, 27 Jun 2007, "Kunde, Brian" writes: >I wish the standard had the margin built in somehow, but that doesn't >seem practical for everyone. They do have margin built-in, but you won't get many to admit it, because it sounds bad, politically. Also, manufacturers can only take advantage of it if they can use the 80-80 rule (which allows a small percentage of non-compliant product to be shipped). Interference that matters results in complaints to authorities. If no-one complains, it can't matter, can it? So it makes economic and practical sense to set the limits so that there is a small but manageable level of complaint. Few will admit that this is what is done, but, whether intentional or not, it IS what happens in many cases. If there are never any complaints, the limit is set too low, maybe a lot too low, isn't it? So the 'margin' is between the actual limit (resulting in, say, 10 complaints a year) and that higher limit (resulting in, say, 50 complaints a year) that would cause the authorities to demand its reduction. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk There are benefits from being irrational - just ask the square root of 2. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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