Thanks for your reply. I have no any idea on any harmful effect in terms of microwave leakage compared with the powdered coating metal housing but had received a couple of questions on it from customers. As I am an electrical engineer, I have very limited knowledge about materials.
Best regards, Scott From: dBaron [mailto:baron...@umn.edu] Sent: Tuesday, September 25, 2007 12:52 AM To: Scott Xe Cc: emc-p...@ieee.org Subject: RE: Microwave leakage In the 70's most all microwave ovens had cavities of stainless steel with some fabricated of aluminum. The primary characteristic of interest is the conductivity of the wall material. Depending on the field distribution in the cooking cavity, there are RF currents flowing in the walls. Again, depending on the details of the 'microwave circuit,' and the load in the oven, these currents can cause localized heating. Since no wall material is a perfect conductor, there will be I2R losses. The penetration depth of the RF currents are also a factor. Way back when, I did some work with combination microwave/thermal energy cooking. The oven thermostat (thermal) sensor came with an iron oxide coating. The coating was relatively resistive and the microwave energy caused currents to flow with resulting resistive heating which messed up the sensing capabilities of the thermostat. Adding a thin, conductive coat of indium to the sensor reduced the currents and, hence, the heating. These effects do not have any noticeable affect on the leakage or on the measurement requirements. Beyond that, I'm not exactly sure what you're asking. Regards, dB On Sep 24 2007, Scott Xe wrote: >Dave, > >Thanks a million to your complete and crystal clear of explanation and >information that are very useful. > >In addition, the latest models of MWO have employed the material of >stainless steel as the housing. Since certain types of the stainless steel >might absorb the microwave energy rather than reflecting it, is there any >additional requirement for this type of MWOs? > >Best regards, > >Scott > >-----Original Message----- >From: dBaron [mailto:baron...@umn.edu] >Sent: Monday, September 24, 2007 1:18 AM >To: Derek Walton >Cc: emc-p...@ieee.org; Scott Xe >Subject: Re: Microwave leakage > >Gentlemen: > >The CDRH/FDA compliance standard is an emission requirement as contrasted >with the ICNIRP or IEEE C95.1 standards which are exposure requirements. It >could, in theory, be possible to check a microwave oven to the ICNIRP >guideline, however, it would be necessary to perform whole-body average >exposure measurements which would (1) be time-consuming and (2) be very >dependent on the location and size of the exposed body. Ovens are typically >tested for emission using a dedicated microwave oven leakage meter (see >http://www.ets-lindgren.com/page/?i=HI-1710A). > >The CDRH/FDA requirements of 10 W/m2 when first received by the end user >and 50 W/m2 thereafter were based on the fact that early microwave ovens >tended to have increased leakage as the oven aged and as the gasketing >materials, often used, would wear. This aging is much less prevalent in >today's oven. > >CDRH has a two documents outlining recommended testing protocols for both >lab testing and field testing of microwave ovens (tried to attach these, >however, the list serve won't accept attachments - happy to forward copies >to anyone interested). In practice, an oven manufacturer must file a >compliance plan with CDRH detailing how they will test and control the >production of ovens to comply with the regulation. > >Regards, > >Dave Baron, PE >Consulting Engineer >Electromagnetic Field Safety >Austin, TX >(512) 917-8346 >d.ba...@ieee.org > > >On Sep 23 2007, Derek Walton wrote: > >> Hi Scott, >> >> thanks for replying. Oh biy, thats really wishy washy isnt it. >> >> I was musing that it would be an ideal use of a small mode stirred >> chamber, if the power density limits could still be used.... >> >> Cheers, >> >> Derek. >> ----- Original Message ----- >> From: Scott Xe >> To: 'Derek Walton' ; emc-p...@ieee.org >> Sent: Sunday, September 23, 2007 4:55 AM >> Subject: RE: Microwave leakage >> >> >> Derek, >> >> >> >> The FDA standard has the limits for first received by the end user and >> thereafter but does not have any recommendation on acceptable method of >> compliance. What is acceptable method in use of this field? >> >> >> >> Thanks and regards, >> >> >> >> Scott >> >> >> >> From: Derek Walton [mailto:lfresea...@aol.com] >> Sent: Thursday, September 20, 2007 11:14 PM >> To: Haynes, Tim (SELEX) (UK Capability Green); Scott Xe; >> emc-p...@ieee.org >> Subject: Re: Microwave leakage >> >> >> >> Hi All, >> >> >> >> This is a new topic for me so please pordon the dumb questions >> >> >> >> Is there a test method for showing compliance with the limit? It seems >> a perfect application for a small mode stirred chamber.... >> >> >> >> Thanks, >> >> >> >> Derek Walton >> >> L F Research >> >> ----- Original Message ----- >> >> From: Haynes, Tim (SELEX) (UK Capability Green) >> >> To: Scott Xe ; emc-p...@ieee.org >> >> Sent: Thursday, September 20, 2007 10:01 AM >> >> Subject: RE: Microwave leakage >> >> >> >> Scott, >> >> You might try relating the leakage level to the public exposure level >> of the ICNIRP recommendations. >> >> I believe that the exposure limit is 1mW/cm2 and would suggest >> looking at the possibility that the user may stay near the unit for 6 >> minutes or more. >> >> >> >> I am not sure of the basis for the 5mW/cm2 under EN 60335-2-25 as it >> is not a specification I use. >> >> >> >> Regards >> >> Tim >> > > >On Sep 23 2007, Derek Walton wrote: > >>Hi Scott, >> >>thanks for replying. Oh biy, thats really wishy washy isnt it. >> >> I was musing that it would be an ideal use of a small mode stirred >> chamber, if the power density limits could still be used.... >> >>Cheers, >> >>Derek. >> ----- Original Message ----- >> From: Scott Xe >> To: 'Derek Walton' ; emc-p...@ieee.org >> Sent: Sunday, September 23, 2007 4:55 AM >> Subject: RE: Microwave leakage >> >> >> Derek, >> >> >> >> The FDA standard has the limits for first received by the end user and >> thereafter but does not have any recommendation on acceptable method of >> compliance. What is acceptable method in use of this field? >> >> >> >> Thanks and regards, >> >> >> >> Scott >> >> >> >> From: Derek Walton [mailto:lfresea...@aol.com] >> Sent: Thursday, September 20, 2007 11:14 PM >> To: Haynes, Tim (SELEX) (UK Capability Green); Scott Xe; >> emc-p...@ieee.org >> Subject: Re: Microwave leakage >> >> >> >> Hi All, >> >> >> >> This is a new topic for me so please pordon the dumb questions >> >> >> >> Is there a test method for showing compliance with the limit? It seems >> a perfect application for a small mode stirred chamber.... >> >> >> >> Thanks, >> >> >> >> Derek Walton >> >> L F Research >> >> ----- Original Message ----- >> >> From: Haynes, Tim (SELEX) (UK Capability Green) >> >> To: Scott Xe ; emc-p...@ieee.org >> >> Sent: Thursday, September 20, 2007 10:01 AM >> >> Subject: RE: Microwave leakage >> >> >> >> Scott, >> >> You might try relating the leakage level to the public exposure level >> of the ICNIRP recommendations. >> >> I believe that the exposure limit is 1mW/cm2 and would suggest >> looking at the possibility that the user may stay near the unit for 6 >> minutes or more. >> >> >> >> I am not sure of the basis for the 5mW/cm2 under EN 60335-2-25 as it >> is not a specification I use. >> >> >> >> Regards >> >> Tim >> >> 6239 >> >> desk A1S77 >> >> P Please consider the environment before printing this email. >> >> >> >> > > > >> >> From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Scott >> Xe >> Sent: Wednesday, September 19, 2007 4:11 PM >> To: emc-p...@ieee.org >> Subject: Microwave leakage >> >> >> >> *** WARNING *** >> >> This mail has originated outside your organization, >> either from an external partner or the Global Internet. >> Keep this in mind if you answer this message. >> >> >> According to EN 60335-2-25, the limit is 5mW/cm2 for type test. Is >> there any other limit for the life span of microwave oven? >> >> >> >> Thanks and regards, >> >> >> >> Scott >> >> - ---------------------------------------------------------------- >> This message is from the IEEE Product Safety Engineering Society >> emc-pstc discussion list. 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Website: http://www.ieee-pses.org/ >> To post a message to the list, send your e-mail to emc-p...@ieee.org >> >> 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 emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org >> >> For policy questions, send mail to: >> >> Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com >> >> 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. Website: http://www.ieee-pses.org/ >> >>To post a message to the list, send your e-mail to emc-p...@ieee.org >> >>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 emcp...@ptcnh.net >> Mike Cantwell mcantw...@ieee.org >> >>For policy questions, send mail to: >> >> Jim Bacher: j.bac...@ieee.org >> David Heald: emc-p...@daveheald.com >> >>All emc-pstc postings are archived and searchable on the web at: >> >> http://www.ieeecommunities.org/emc-pstc >> > > -- dBaron dB-emf (512)917-8346 d.ba...@ieee.org - 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 emc-p...@ieee.org 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 emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
