While slightly off-topic, this discussion got me thinking about the measurement of the voltage on the cable. If done with a RF cable current clamp, do you have to do a conversion of some sort if the cable is assumed to be 150 ohms?
For a 50 ohm system, a 3V level measured with a clamp would be 96 dBuA minus the transfer impedance in dB ohms. If the cable is 150 ohms though does that mean you are measuring the equivalent of 1V from the clamp instead of 3V because the clamp is measuring current? Stated another way, assuming the transfer impedance of the current clamp is zero to simply things, for an assumed 150 ohm cable should you be reading 96 dBuV on a spectrum analyzer hooked up to the probe or something less that than equivalent to 1V? Never worked with this stuff so I’m curious. Dan From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Ken Javor Sent: Thursday, June 26, 2008 11:14 AM To: Untitled Subject: Re: EMC in the news: RFID & Medical Comment (e) is unrealistic. Assuming 61000-4-6 was applied, the amount of power required to directly inject 1, 3 or 10 Volts oc into 150 Ohms is well above the radiated power from an rf id device. Ken Javor Phone: (256) 650-5261 ________________________________ From: "Conway, Patrick R (Houston)" <p.con...@hp.com> List-Post: emc-pstc@listserv.ieee.org List-Post: emc-pstc@listserv.ieee.org List-Post: emc-pstc@listserv.ieee.org Date: Thu, 26 Jun 2008 14:17:00 +0000 To: Gert Gremmen <administra...@ce-test.info>, "Rudd, Adam" <ar185...@ncr.com>, "emc-p...@ieee.org" <emc-p...@ieee.org> Conversation: EMC in the news: RFID & Medical Subject: RE: EMC in the news: RFID & Medical Gert- You mention one possible reason for the test results is that the EUT's have immunity deficits. I agree, that is one possibility. here are a few other possibilities: (BTW- not affiliated in any way with medical devices nor with, all comments OOO ) b) Could it be a systemic testing error? Was a shield room used? Were the ambients controlled and eliminated? Were the devices connected to a patient simulator? Did the test engineer have his personal GSM phone "OFF"? etc. (...crazier things have happened.) c) Maybe the EUT are old. Through outdated design specs perhaps RFID proximity was not a consideration during their design. And yet, in today's hospitals, the two types of devices may be in close proximity. If this is the case then the study has done a great service to the community by uncovering a problem that was unknown. d) Maybe the EUT are old (not a repeat) Through many years of use perhaps once immune equipment has lost some of their designed immunity? Again- if this is the case this study may have uncovered a previously unknown problem. e) Is it possible for an RF ID device to overwhelm the immunity levels of the EUT? If a medical device is tested at 10 V/m and an RFID device TXout is in the mW range- is it possible for a RFID mW transmitter to generate 10 V/m? Perhaps. For instance- since an RFID device operating at 125 kHz in not transmitting in the classic sense, then there may be near-field resonant effects that are not previously understood in the medical device immunity requirements? It seems that we, as professionals in this field, have the unique ability to analyze these reports like no other community can. I wonder if we will find the answers to the large number of questions raised by the article. All comments OOO. Best Regards, Patrick. p.con...@hp.com ________________________________ From: Gert Gremmen [mailto:administra...@ce-test.info] Sent: Thursday, June 26, 2008 2:57 AM To: Conway, Patrick R (Houston); Rudd, Adam; emc-p...@ieee.org Subject: RE: EMC in the news: RFID & Medical The report was produced by TNO, a Dutch private organization (http://www.tno.nl/content.cfm?&context markten&content=markt_persbericht&laag1=189&item_id=200806250026&Taal=2 <http://www.tno.nl/content.cfm?&con ext=markten&content=markt_persberic t&laag1=189&item_id=200806250026&Taal=2> <http://www.tno.nl/content.cfm?&context markten&content=markt_persbericht&laag1=189&item_id=200806250026&Taal=2> ) and some results are available here: http://www.amc.nl/?pid=5266 Manufacturers name and equipment type included. Please note that the energy levels of RFID are in the milliwatt range, so all problems are to be categorized as immunity deficits. It is astonishing that the security of healthy persons (like car drivers) is taken much more seriously (by car manufacturers for example ) as the security of people with bad health like in hospitals. Most medical equipment is tested at 10 V/meter or less. where critical car parts must be tested up to 200V/m. Cars are to be sold at low prices (relatively) , medical equipment at sky-high costs. It seems that emc quality is the inverse of the costs of equipment. Where much attention is given to reliability and electrical safety of medical equipment, emc is still neglected. Note that this investigation was made in a Dutch University Hospital; On European soil , where immunity requirements have been virtually law since 1996 !!!! The lack of EMC care might be related to the fact that medical accidents are easy to cover up, (more easy then car accidents) and liability of medical staff is difficult to prove, let alone the liability of a medical equipment manufacturer. See the discussion on the Therac-25. Gert Gremmen Van: emc-p...@ieee.org [mailto:emc-p...@ieee.org] Namens Conway, Patrick R (Houston) Verzonden: Wednesday, June 25, 2008 4:08 PM Aan: Rudd, Adam; emc-p...@ieee.org Onderwerp: RE: EMC in the news: RFID & Medical ...and if you put four of them in a circle, you can pop corn. :) Best Regards, Patrick. p.con...@hp.com ________________________________ From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Rudd, Adam Sent: Wednesday, June 25, 2008 7:19 AM To: emc-p...@ieee.org Subject: EMC in the news: RFID & Medical “The latest research, conducted at Vrije University in Amsterdam, tested the effect of holding both "passive" and powered RFIDs close to 41 medical devices, including ventilators, syringe pumps, dialysis machines and pacemakers. A total of 123 tests, three on each machine, were carried out, and 34 produced an "incident" in which the RFID appeared to have an effect - 24 of which were deemed either "significant" or "hazardous". In some tests, RFIDs either switched off or changed the settings on mechanical ventilators, completely stopped the working of syringe pumps, caused external pacemakers to malfunction, and halted dialysis machines. The device did not have to be held right up to the machine to make this happen - some "hazardous" incidents happened when the RFID was more than 10 inches away.” --http://news.bbc.co.uk/2/hi/health/7471008.stm <http://news.bbc.co.uk/2/hi/health/7471008.stm> <http://news.bbc.co.uk/2/hi/health/7471008.stm> Best Regards, Adam Rudd Electrical Engineer (EMC) NCR Corporation, RHSS Duluth, GA (770) 495-2825 - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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