All good points but none in conflict with what I said. Your example of the ultrasound machine on a cart (with attendant cables) definitely qualifies as a large item, even if the ultrasound equipment enclosure itself is small. This is where I mentioned the control of cable currents, which can easily be extended to power feeders, whether using an absorber clamp or the LISNs themselves. If you do want to use the LISNs, however, it will be necessary to limit the power feeder length to about one foot so that the LISNs are within a tenth wavelength of the EUT and we don't introduce vswr-related errors. That isn't a fundamental problem in the aerospace world where I mostly work, but it is a big deal in he commercial world because they like to use the equipment-provided power cord.
From: "Garnier, David S (GE Healthcare)" <[email protected]> List-Post: [email protected] Date: Tue, 19 Jun 2007 13:22:52 -0400 To: <[email protected]> Subject: FW: RE Measurement Distance per EU Ken, 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 some correlation 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]> List-Post: [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 meter testing. 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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