Nancy, Several things: (1) Importance of conductivity-the rf wave is confined to what is called the classical skin depth thichness. 99% of the rf waves energy is confined to 3 X the classical skin depth thickness, for iron 3 X 0,0003 inch(at 1 MHz) = 0.0009 inchs; and 3 X 0.00004(at 1000 MHx or 1 GHz) = 0.00012. So even if the steel is exposed the wave will not penetrate the steel. Zn is even better conductance than iron. The classical skin thickness is proportaional to the inverse of the sq rt of the conducivity. The difference of the DC valves of 0.3 and 0.4 will never be see at the Shielding Effectiveness point of view
(2) The shielding effectiveness of the enclosure will depend on the openings rather than the material properties. (3) You are correct on welding the Zn plated steel the Zn will be evaporated near the weld and will can corrosion. What should be done is to out the Zn back to the same thickness. There are several techniques people use to do that talk. If you need more back up you could arrange for a conference call between me, your customer and y6ourself and if needed I will spend a few going going thur the background nesseary to convince your customer otherwise welcome to our e-mail group. Thanks Richard Haynes 609-497-4584 -----Original Message----- From: Bailin Ma <[email protected]> To: [email protected] <[email protected]>; [email protected] <[email protected]>; [email protected] <[email protected]> List-Post: [email protected] Date: Wednesday, October 14, 1998 10:16 PM Subject: Re: Conductivity Question >Hi Nancy, > >The following is my two cents worth. Please correct me. >>I have done a ohms test on the two materials. Both testing at .3 to .4 >ohms. >> My customer has already gone through their EMI Testing... > >It seems to me that only data of .3 and .4 ohms is not enough. We still >don't know the thickness of the coating, and also the data is only DC value >instead of RF value. Do you know how much margins of the EMI test your >customer has got with the original case? Even though we know all necessary >data, it's still very hard to say what role the conductivity plays in the >final EMI profile of the EUT, which depends on too many parameters. > >We have to do some test. If your customer was reluctant to redo the EMI >test, can you suggest a Shielding Effectiveness (SE) comparison test? The >test needs only two empty cases with a comb generator inside. The SE test >results are straightforward to convince your customer. > >Best Regards, >Barry Ma > > >------------- >Original Text >From: <[email protected]>, on 10/14/98 1:17 PM: >Hello Group! > >The following is a non-member post which was submitted to the admins, but >which really ought to be posted. (If you post a reply, remember to copy >Ludvigsen, but not me.) > >------------------------ > From: Nancy Ludvigsen <[email protected]> > Subject: Conductivity Question > Date: Wed, 14 Oct 1998 15:53:56 -0500 > To: "'[email protected]'" <[email protected]>, >"'[email protected]'" <[email protected]> > > >> Hi Guys: I am a manufacturers rep. for a sheet metal fabricator. I have >a customer that is currently manufacturing an enclosure our or Galvannel. >This unit is welded and they are not currently painting over the welded >areas. This will cause corrosion over time. >> >> I am suggesting that they go to a zinc plated cold rolled steel for a >better finish, and also our buying power is suited for steel. >> >> My customer has already gone through their EMI Testing and is hesitant to >change to zinc plated cold rolled steel because they do not know the >difference in conductivity between the two materials. >> >> I have done a ohms test on the two materials. Both testing at .3 to .4 >ohms. >> >> Can you direct me to a source to get more information on the conductivity >of the two metal finishes? Or give me more direction as to how to address >this issue? >> >> Any information is greatly appreciated. Thank you in advance. >> >> Nancy >> > > >-------------------------- >Ed Price >[email protected] >Electromagnetic Compatibility Lab >Cubic Defense Systems >San Diego, CA. USA >619-505-2780 >Date: 10/14/1998 >Time: 12:17:52 >-------------------------- > > > >--------- >This message is coming from the emc-pstc discussion list. >To cancel your subscription, send mail to [email protected] >with the single line: "unsubscribe emc-pstc" (without the >quotes). For help, send mail to [email protected], >[email protected], [email protected], or >[email protected] (the list administrators). > > > >--------- >This message is coming from the emc-pstc discussion list. >To cancel your subscription, send mail to [email protected] >with the single line: "unsubscribe emc-pstc" (without the >quotes). For help, send mail to [email protected], >[email protected], [email protected], or >[email protected] (the list administrators). > > --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
