Dear All, Thank you very much for those who have replied online and offline. Special thanks to two members who provided me with a copy of MIL-STD-285. I have learned that this mil standard obsoleted 10 years ago. Its replacement is IEEE-STD-299. We basically used this IEEE standard for the shielding test. My manager held on the installation of ferrite tiles until the completion of the shielding test. According to the installer, typical spec is 100dB. Based on members' calculation and recommendation (and budget concern), I requested 106dB. Due to this additional 6 dB, the test equipment provided by the chamber manuacturer does not have required 6 dB dynamic range, a third party (test house) conducted the test. One interesting thing found during shielding test while riding up and down with the test technician. The technician checked all the seems. Some places were quiet (no signal detected). Some places had signal detected. In contrast, it seemed the signal (10GHz) was all over the air. I doubled check the level. It met the spec. Best regards, Grace On 1/27/08, E. Robert Bonsen <[email protected]> wrote:
Hi Grace, The answer to your question has both a technical and a contractual component to it. It becomes more difficult to fix any shielded room issues when tile is already installed. Fixes for shielding issues often affect a larger area when gasketing material or braces are to be replaced, sometimes panels if a penetration (or door) is the culprit. If the issue is pinpointed to a particular seam through experimentation, you would be relatively safe installing tile in the areas outside of the panels/mounting hardware associated with that seam. Other walls not affected by the shielding breach would be relatively safe as well. Shielding effectiveness testing at higher frequencies, if done correctly, is not negatively affected by absorbers mounted outside the immediate test area. For most chamber builds not done by a single integrator, the shielded room contractor or installer is only responsible for delivery of an empty shielded room that meets shielding effectiveness specifications. Once someone else (absorber installer, customer) installs anything in that room, this clear responsibility becomes blurry since it can be argued that the continuing shield failure is completely or partially due to the added material or the installation process thereof. It is very difficult to argue against this without significant additional testing, which adds cost. If the chamber installation is done by a chamber integrator, they are responsible for all aspects of performance so they would have to make the call on when it is appropriate to start the tile installation. I would advise against installing tile before the shielded room meets the specification, unless you are absolutely sure doing so will not interfere with any contractual obligation on behalf of the shielded room manufacturer and/or installer. One additional comment: Based upon my experience designing and building chambers as well as using them, I recommend clients to perform a shielding effectiveness verification after completion of the ferrite tile installation, before any foam absorbers go in. The reason for this is three-fold: Firstly, methods used for ferrite installation often require partially breaching the integrity of the shield. Secondly, the tile installation process can easily stress filter and other hardware installed. Thirdly, the weight of the ferrite tiles is considerable and will stress the room structure differently than when it is empty, possibly opening up seams. Note that this would mostly be an issue with lower quality (cheap) shielded room installations. As product testing will be done in the absorber lined room it is always good to confirm the shielding quality of the final chamber, or at least close to it. The timing for the verification test (before any foam installation) is due to the need to be able to still fix issues and the ability to pinpoint issues. Once the foam is up fixing issues requires major tear-down work and it is not easy to get close to the wall for debug work. Hope this helps. Best regards, -Robert Grace Lin wrote: > Dear Members, > > Is it OK to start ferrite tile installation before the completion of > shielding test during the construction of a 3m EMC semi-anechoic > chamber? More specifically, if a particular area, such as door seam, > does not meet the proposed specification, is it OK to start ferrite > tile installation on the area away from the door? If yes, how far to > keep away from the door? > > Thank you very much for your time and look forward to your help. > > Best regards, > Grace > - ---------------------------------------------------------------- > 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. 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
