We have been discussing this topic in NEC1 as the Dutch shadow committee for CISPR/CENELEC with this standard. The purpose of the clause is to create a well defined reproducible situation, and not a worst case situation. I have always opposed such a scenario, as every EMC engineer knows cables in reality do not hang as in CISPR, and the fixed length prescribed in CISPR 22 does create blind spots in the frequency spectrum. A fixed length cable radiates well (resonance) for a 1/4 lambda length and every impair multiple of it. It creates nulls for every pair multiple. Although the null effect diminishes (so does the resonance) for lengths that are a large multiple of 1/4 lambdas (or for higher frequencies: essentially the same) the effect can be disastrous if your problem frequency is exactly matching the cable length as prescribed. At 80 cm cable length this cable setup resonates at 300/(4x0,8) = just below 100 Mhz in the middle of the FM band. The first null happens to be at just below 200 Mhz , popular emissions problem frequency. Although the quality factor of the resonance and null effect is not very high, the differences easily add up to 10-20 dB. This is a large (and systematic) error in a system where the measuring receiver is bound to meet 1 dB accuracy. By creating a left right symmetrical situation the effect gets accentuated.
My opinion was not shared by the Dutch committee, as they felt reproducibility more important then measuring the exact amplitude of the emitted value. This is what happens if bureaucracy meets technicians..... I strongly support your way of testing, and even want to go further. I believe that emission of equipment must be essentially independent of cable length, and cable load. This approach requires low frequency (< 100 Mhz) emission measurements on cabling to be carried out using CDN's (in addition to the enclosure) where the contribution of the emission spectrum by cable CM current must essentially approach zero (compared to the enclosure emission). This way we would get rid of prescribed cabling schemes and annihilate emission spectrum problems caused by erronic construction or cable routing. This is very important as f.a. automotive electronics get more and more dependent of correct cabling and cabling quality and we can imagine what happens with the EMC quality of screening and grounding in a cabling hostile environment as a car. Recently test were carried out with modern cars that could be easily sabotaged on large (hundreds ? m) distances using microwave(?) power transmitters (pulse) to the point of getting defective. Imagine this technique in the hand of potential terrorists on board of a small lorry or simply on the ground. The tests were not yet carried out on commercial air planes while landing or starting. (You will excuse me if I leave out specific details about frequency and power on this forum). Most of these problems could be avoided by decently screening our electronics and effectively filtering in- and outputs, to the point of letting no RF-signals in or out. For higher frequency data carrying signals appropriate filtering techniques are available such as symmetrical data transfer and CM coil constructions. (But don't rely on the lousy way 100baseT networks are designed; they can be affected too easily due to their awful CM suppression for even 60Hz, I can tell you stories about 3COM products and others) This really gets off topic now so I'll stop. Regards, Gert Gremmen, (Ing) ce-test, qualified testing =============================================== Web presence http://www.cetest.nl CE-shop http://www.cetest.nl/ce_shop.htm /-/ Compliance testing is our core business /-/ =============================================== >>-----Original Message----- >>From: [email protected] >>[mailto:[email protected]]On Behalf Of Alex McNeil >>Sent: Tuesday, November 27, 2001 6:53 PM >>To: 'emc-pstc' >>Subject: EN55022/CISPR22 Cable Layout >> >> >> >> >>Hi All, >>I am not 100% clear on the statement regarding cable layout in Figure 10 >>"Test Configuration: tabletop equipment (radiated measurement)" >>It says: >>1. If cables which hang closer than 40cm to the horizontal metal ground >>plane cannot be shortened to appropriate length, the excess shall >>be folded >>back and forth forming a bundle 30cm to 40 cm. >> >>What does it mean when it says "...cannot be shortened to appropriate >>length...? This conflicts with section 8.1 which says you must >>test with the >>lengths specified for the product. >> >>I bundle various 2m and 3m length cables that are intended to be connected >>to an EUT peripheral horizontally and those that are intended to be >>connected to the PSTN, or other external termination point, vertically. >>Also, PSU's on the floor with an output lead to the EUT is bundled >>vertically. Normally there are no peripherals, or PSTN, attached but I >>connect the cables anyhow for worst case. I do not connect >>similar interface >>ports, only one of the same type. It all becomes rather "messy" or "busy" >>with lots of bundled cables. >>Once I have found the worst case emissions cable setup, I "tape" these in >>position to a hanging nonconductive surface and take a photograph. This is >>for repeatability in future audit testing. >> >>Am I doing this wrong? It would seem from the diagram that you have the >>option to "shorten to appropriate length" e.g. 1M? Also it looks >>as if the >>vertical cable shown is only 40cm? >> >>I am sure someone out there knows exactly how it should be done or is the >>standard not clear? >> >> >>Kind Regards >>Alex McNeil >>Principal Engineer >>Tel: +44 (0)131 479 8375 >>Fax: +44 (0)131 479 8321 >>email: [email protected] >> >> -----Original Message----- >>From: Mark Pascarelli [mailto:[email protected]] >>Sent: Monday, November 26, 2001 4:47 PM >>To: 'emc-pstc' >>Subject: Frame Surge Test >> >> >> >>Hi all, >> >>I am trying to re-design our current power supply to meet GR-1089-Core >>Specification. >>The Power Supply has a -48V input and 5VDC/100W, 5VDC/100W and 12VDC/150W >>Output. >> >>Based on current testing, we did not comply with Section 9.10.6 >>Frame Surge >>Test. >>This test applies a surge current as defined in IEEE C62.41. The filter >>capacitor was destroyed during this test. The capacitor is rated >>at 100V. I >>think this capacitor should be replaced with a higher voltage X or Y >>capacitor. Possibly a GDT or TVS is required. >> >>If anyone can help, I will email a portion of the schematic in >>PDF format. >> >>Thank you, >> >>Mark Pascarelli >>Electrical Engineer >>Carlo Gavazzi, Inc. >> >>------------------------------------------- >>This message is from the IEEE EMC Society Product Safety >>Technical Committee emc-pstc discussion list. >> >>Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ >> >>To cancel your subscription, send mail to: >> [email protected] >>with the single line: >> unsubscribe emc-pstc >> >>For help, send mail to the list administrators: >> Michael Garretson: [email protected] >> Dave Heald [email protected] >> >>For policy questions, send mail to: >> Richard Nute: [email protected] >> Jim Bacher: [email protected] >> >>All emc-pstc postings are archived and searchable on the web at: >> No longer online until our new server is brought online and the old >>messages are imported into the new server. >> >> >>------------------------------------------- >>This message is from the IEEE EMC Society Product Safety >>Technical Committee emc-pstc discussion list. >> >>Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ >> >>To cancel your subscription, send mail to: >> [email protected] >>with the single line: >> unsubscribe emc-pstc >> >>For help, send mail to the list administrators: >> Michael Garretson: [email protected] >> Dave Heald [email protected] >> >>For policy questions, send mail to: >> Richard Nute: [email protected] >> Jim Bacher: [email protected] >> >>All emc-pstc postings are archived and searchable on the web at: >> No longer online until our new server is brought online and the old >>messages are imported into the new server. >> >>------------------------------------------- >>This message is from the IEEE EMC Society Product Safety >>Technical Committee emc-pstc discussion list. >> >>Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ >> >>To cancel your subscription, send mail to: >> [email protected] >>with the single line: >> unsubscribe emc-pstc >> >>For help, send mail to the list administrators: >> Michael Garretson: [email protected] >> Dave Heald [email protected] >> >>For policy questions, send mail to: >> Richard Nute: [email protected] >> Jim Bacher: [email protected] >> >>All emc-pstc postings are archived and searchable on the web at: >> No longer online until our new server is brought online and >>the old messages are imported into the new server. >> >>
<<attachment: Gert Gremmen.vcf>>
