Brian- While I agree that dictating the exact routing of a cable though the clamp is straining at gnats, it could make a (small) difference even in the case using feedback as outlined in IEC 61000-4-6. According to the standard, the calibrated voltage needs to be induced on the cable, and the current monitored. ONLY IF the resulting current is higher than what the voltage would cause to flow into 150 ohms is the drive reduced to adjust the injection current. This means that for cables to the EUT that present a load above 150 ohms, there is no adjustment to the drive. So it is conceivable that if the cable layout in the clamp does not match the cable layout used when calibrating the drive to the clamp, then the induced voltage might be lower than if the cable layout did match the calibration layout. And since the current measured with the current probe is too low, the drive is not adjusted.
Let me say again that this is straining gnats. There are too many variables. The cable to the EUT seldom matches that used during calibration. The source impedance of the drive from the clamp is not as well controlled as that of a CDN. If it has a source impedance higher than 150 ohms, and the cable into the EUT presents an impedance higher than 150 ohms, the voltage induced onto the cable will be higher than if the clamp had a nice source impedance of 150 ohms. Thus we are over testing. To the current probe everything looks OK, so we don't know we are over testing. All of us (including auditors) just need to get over it. Let's make a good effort at doing the test properly, and not get too excited about these fine points until someone can show that they really matter a bunch, and can come up with a better, reasonable procedure (or better clamp). Cheers, Donald Borowski EMC Compliance Engineer Schweitzer Engineering Labs Pullman, WA, USA From: "Kunde, Brian" <[email protected]> To: "[email protected]" <[email protected]> Date: 11/20/2012 09:53 AM Subject: RE: Fischer CC EM Clamp F-203I-32mm Sent by: [email protected] Our clamp has three half moon shaped spring loaded ferrite pieces that holds the cable in the bottom of the clamp’s ferrite cores, so such spacers would not work for me. I can make an argument that the cable is run the same way that it is when my clamp is calibrated so any alteration to that setup would be wrong to apply. Plus, if you use the feedback method where you are reading back the injected rf with a current clamp then what does it matter how the cable goes through the clamp? Some of these auditors really drive me nuts. Brian From: Sundstrom, Michael [mailto:[email protected]] Sent: Tuesday, November 20, 2012 12:42 PM To: Kunde, Brian; [email protected] Subject: RE: Fischer CC EM Clamp F-203I-32mm I once had an auditor who dinged me on not keeping the cables centered in the injection clamp. Next day I had foam cell material in the clamp, pretty much kept the cables centered. I don’t think it made much difference??? Well, no difference that I could see… Michael Sundstrom OHD TREQ Dallas Electronic Lab Analyst EMC Lead (214) 579 6312 office (940) 390 3644 cell マイク KB5UKT From: Kunde, Brian [mailto:[email protected]] Sent: Tuesday, November 20, 2012 11:15 AM To: [email protected] Subject: Re: [PSES] Fischer CC EM Clamp F-203I-32mm Wendy, Who makes an EM Clamp that has a cable entry of 30mm? The size of the cores needed to handle a cable diameter of any size will be large enough to make this difficult if not impossible. Plus you have to have room for the input ‘N’ connector mounted under the cores. I have never seen an EM Clamp where the cable entry wasn’t 50mm or greater though I’m not saying one doesn’t exist. Typically they are more like 75mm. I don’t know where your supplier got this requirement. I don’t have the latest version of the 4-6 standard but the copy I have only states in section 7.2, “The cable between the AE and the injection clamp shall be kept between 30mm and 50mm above the ground reference plane”. The text doesn’t say anything about the height of the clamps or the cable height between the clamp and EUT, though the picture in figure 6 shows it as 30mm. I don’t see where the short distance the cable has to run higher than 30-50mm coming in and out of the clamp would have much impact on the test results. The Other Brian From: [email protected] [mailto:[email protected]] On Behalf Of Wendy Nya Sent: Tuesday, November 20, 2012 7:50 AM To: EMC- PSTC Subject: Fischer CC EM Clamp F-203I-32mm Dear All, We have a very old Fischer CC F-203I-32mm EM Clamp. A supplier pointed out that it does not comply to the 61000-4-6 standard's requirement - the height of the cable entry is more than the standard's requirement of 30-50mm. I just checked Fischer CC website. They are still selling this model. Is anyone still using it? Regards, Wendy - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ 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]>
