With all the talk about 3m chambers, I wonder what we all picture as a '3m chamber'.
EN55022:1998 Figure 2 shows a drawing for an alternative test site that gives minimum dimensions. - Main axis: about 3 x 3m (30 ft.) - Width: a little over 6m (20 ft.) - Height: sufficient to raise the antenna to 4m, with a 1m antenna element, separated 1m from the ceiling - about 6m (20 ft.) If absorber cones are used, add about 2m to the length & width, and 1m to the height. This totals to about 11m x 8m x 7m. I may have the dimensions a little wrong. But even with corrections, that's a lot bigger than the average 3m chamber I've seen! The room has to meet site attenuation values, as well. I wonder what our experiences would be with 3m chambers that met all these requirements. Pat Lawler EMC/Reliability Engineer SL Power Electronics Corp. "Garnier, David S (GE Healthcare)" <[email protected]> wrote on 06/19/2007 10:22:52 AM: > I agree with most everything you have said concerning 10 meter > sites but I am going to play > the heretic role against 3 meter chamber usage. > > We build and test large product here, CT, CT/Pet, X-ray systems, > (EUT's often weight close to > 12 tons.) It's very common today to have hospitals order 2 or 3 > phase UPS's with our systems, > data backup during weekly emergency generator testing or riding out > power glitches during > electrical storms. > > My negative experience with 3 meter chambers is the following. > > Unfortunately, some of our UPS vendors like to certify their > products in 3 meter chambers. > I wish I had a 100 dollars for every conversation that has ensued, > "No, your 3 meter radiated > emission test data does not correlate to our 10 meter chamber > for 100 MHz and below." "Why?" > I think UPS's are evil but that's a different subject. ;-) > > We also build smaller diagnostic products, such as roll around, > plug into 120 Vac 15A outlet > Ultrasound machines. For example, if we test this product in our 3 > meter chamber we will not > see 100 MHz and below board band radiated emissions, same situation > as 3 meter RE test > data for UPS's. > > For the sake of discussion, I would support 3 meter chamber usage > for 100 MHz and below > *IF* the requirement for AC line conducted emission were raised to > 100 MHz. I bet then we > would see somecorrelation to 10 meter RE data. > > 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 Ken Javor > Sent: Monday, June 18, 2007 2:51 PM > To: [email protected] > Subject: Re: RE Measurement Distance per EU > > It seems clear to me, from this post and what I know, that the 10 > meter site is the gold-standard. If I were a commercial test > facility, or an in-house test facility for a company making large > products, a ten meter site would be the way to go. > > But if I were a PC manufacturer, or if I qualified items that size > or smaller, I can see no justification whatsoever for the huge cost > of the ten meter chamber vs. a three meter chamber. As long as I > am already using a biconical antenna instead of a tuned dipole at > the low end, I see no cost-effective rationale for the larger chamber. > > Even if my small test item might have a long cable attached to it, > I ought to be able to control the cable common-mode current > emissions using a current probe or absorbing clamp and be able to > generate a limit for those currents commensurate with the radiated > emission limit at three or ten meters. > > This approach is not new, it dates back to at least the 1980s, with > a series of papers given at the Zurich symposia by Mr. Balint > Szentkuti (e.g., Szentkuti, B., Give Up Radiation Testing In Favour > Of Conduction Testing, Proceedings, EMC Zurich 1989). > > I'm not advocating elimination of radiated testing, but simply > recognizing that emissions emanating from long cables are more > accurately measured and controlled as currents than as fields, not > to mention much less expensively. For precisely the same reason > that 61000-4-6 is performed in lieu of 61000-4-3 below 80 MHz. > > From: "Kunde, Brian" <[email protected]> > Date: Mon, 18 Jun 2007 15:32:32 -0400 > To: "Grace Lin" <[email protected]>, <[email protected]> > Subject: RE: RE Measurement Distance per EU > > Grace, > > Do they make a fully compliant 3 meter semi-anechoic chamber? I > wasn't aware that a 3 meter chamber passed the NSA requirements > down to 30Mhz. > > The purpose of having a Test Standard is to standardize on a method > in which testing is performed so the results can be repeated at > other test sites and hopefully have the same or similar results. > When you stray from what the standard calls out, then you take the > risk of your results being brought into question. > > I think your biggest problem with testing at 3 meter is going to be > with near field below 100Mhz. Because of the common differences seen > when testing a product at 3 meter verses 10 meter, I think there > will always be a high level of doubt in your test results. > > In my opinion, "compliance testing" can only be confidently done at > a 10 meter OATS or equivalent. > > BTW, the note in section 10.2.1 is a method to test signals that > fall near or on a high ambient. Most all OATS have at least a few > areas with high ambient and this section gives them a work around > at only those frequencies. It is not intended to allow full testing > at distances than 10 meter. In a chamber you wouldn't have any > ambient signals so you couldn't use this section to justify 3 metertesting. > > I am very curious to know the confidence level of 3 meter chambers > are. Maybe some who have such chambers will post. > > The Other Brian. > > From: [email protected] [mailto:[email protected]] On Behalf Of Grace Lin > Sent: Monday, June 18, 2007 1:43 PM > To: [email protected] > Subject: RE Measurement Distance per EU > > Dear Members, > > Is 3m measurement distance for radiated emission not accepted by EU? > > I propose a 3m full compliant chamber. A chamber manufacturer > informs me that EU only accepts 10m measurement distance. I > checked EN 55022: 1998 incorprating Corrigendum Nol 1 and A1 and > A2. Clause 6 states: > > "The EUT shall meet the limits of Table 5 or Table 6 when measured > at the measuring distance R in accordance with the methods > described in Clause 10. ... " > > The title of Table 5 is: "Table 5 - Limits for radiated disturbance > of class A ITE at a measuring distance of 10m". The title of Table > 6 is: "Table 6 - Limits for radiated disturbanc eof class B ITE at > a measuring distance of 10m". Subclause 10.2.1 states: > > " > 10.2.1 Antenna-to-EUT distance > Measurements of the radiated field shall be made with the antenna > located at the horizontal distance from the boundary of the EUT as > specified in Clasue 6. > > NOTE If the field-strength measurement at 10m cannot be made > because of high ambient noise levels, or fo rother reasons, > measurement of class B EUT's may be made at a closer distance, for > example 3m. An inverse proportionality factor of 20 dB per decade > should be used to normalize the measured data to the specified > distance for determining compliance. Care should be taken in the > measurement of large EUTs at 3m at frequencies near 30 MHz, due to > near field effects. > " > > I look forward to your comments. > > Best regards, > Grace Lin > Crestron Electronics, Inc. > www.crestron.com <http://www.crestron.com> > > - ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. 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