RE: Comparing EMI test results
Hi All, Thanks everyone who replied and offerred their suggestions regarding this topic. Praveen I'm trying to setup a programme to compare test results (for Radiated Emissions) between test labs. The plan is to circulate a Artifact around the labs and compare the results. The test sites being compared are Semi-anechoic Chambers v/s OATS. The source used is a wideband RF comb generator. I would like to understand the concept fully before I initiate this programme. Is there any information readily available on this topic? Any help will be greatly appreciated. Thanks. Praveen Thanks for the response. The purpose is to test both, the facility (semi-anechoic v/s OATS) and the quality of results. The comb generator is my first approach. A standard test sample(with cables) will follow. Any procedures, data, results, experience on this issue ? --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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.
RE: Comparing EMI test results
We have also performed some experimentation with our compact semi-anechoic chamber (prescan) and OATS, both at 3 meters. Our experience correlates with Doug's. For devices as small as say a shoebox, our correlation is typically within 2 dB. For systems that are 1.5 meters and floor mounted with a few interconnecting cables, our correlation is typically within 4 dB. We have seen an occasional emissions in the chamber that did not show up on the site. As we use a bilog in the chamber and use bicon and log periodic on the site, we did not pursue the why. I would assume that it is related to the imperfect absorption of the chamber compared to the open space of the OATS. Another part that might make a difference in your measurements is the conditions at each site. Our chamber is a fairly constant 72 degrees, 50% humidity producing a constant NSA. The OATS, however, varies in its moisture content which we have learned contributes to the variation between chamber and OATS. When the site is dry, we get a down the middle NSA; when it is soaked, we get closer to the NSA limit and also a larger variation between the chamber and OATS as would be expected. We have not yet discovered why the moisture affects the NSA. On the other hand, the OATS is compliant and we have learned to deal with the degrees of variation, so at this point we live with it. Don Umbdenstock -- From: Doug McKean[SMTP:dmck...@auspex.com] Reply To: Doug McKean Sent: Monday, January 07, 2002 1:44 PM To: EMC-PSTC Discussion Group Subject: Re: Comparing EMI test results Not to rain on the parade, but be careful when comparing semi-anechoic chambers versus OATS that are of different distances, i.e. 3m vs. 10m. You may get not only widely different measurements even when compensating for the distances, but you may also obtain different frequencies. On two occasions, I've had frequencies show up rather prominently in the chamber prescan not to be seen to any significance at an OATS. In other words, to get a fairly reliable comparison between a chamber and a site, in my opinion, you'll first have to compare a 10m chamber with a 10m OATS. Then, work backwards to a 3m chamber. You will also have to develop a fudge factor for the size of the EUT. The size can effect results as well. You may get good correlation with a small tabletop EUT and terrible correlation to a much larger device. Possible reasons for this I'll leave to discussion. But suffice it to say, the closer the product is to a point source the better the correlation. The farther the product is from a point source, the worse the correlation. At least in my experience. Name the site with which you will be getting an official measurement as your standard, then work all the others in reference to it. The standard site will be the one which will have the final say. Sorta been there ... Done that ... etc ... Sorta gave up. - Doug McKean --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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.
Re: Comparing EMI test results
Not to rain on the parade, but be careful when comparing semi-anechoic chambers versus OATS that are of different distances, i.e. 3m vs. 10m. You may get not only widely different measurements even when compensating for the distances, but you may also obtain different frequencies. On two occasions, I've had frequencies show up rather prominently in the chamber prescan not to be seen to any significance at an OATS. In other words, to get a fairly reliable comparison between a chamber and a site, in my opinion, you'll first have to compare a 10m chamber with a 10m OATS. Then, work backwards to a 3m chamber. You will also have to develop a fudge factor for the size of the EUT. The size can effect results as well. You may get good correlation with a small tabletop EUT and terrible correlation to a much larger device. Possible reasons for this I'll leave to discussion. But suffice it to say, the closer the product is to a point source the better the correlation. The farther the product is from a point source, the worse the correlation. At least in my experience. Name the site with which you will be getting an official measurement as your standard, then work all the others in reference to it. The standard site will be the one which will have the final say. Sorta been there ... Done that ... etc ... Sorta gave up. - Doug McKean --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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.
RE: Comparing EMI test results
I agree absolutely with Brent. Also, even if ALL the other variables are STRICTLY controlled you could conciveably get as much as 8 db variation between sites. I suggest ( as Brent has already done) getting Lowell Kolbs paper on site comparisons. From: Brent DeWitt bdew...@ix.netcom.com Reply-To: Brent DeWitt bdew...@ix.netcom.com To: Rao, Praveen praveen@fujitsu.com.au, emc-p...@majordomo.ieee.org Subject: RE: Comparing EMI test results Date: Sun, 6 Jan 2002 22:46:22 -0700 Rao, The comb generator is not a bad choice, but a few things should be checked (yes, I've done this). First, establish the base variation in the source. No antenna, just a direct connection to the receiver/SA that you will use for the evaluation under an expected, reasonable variation in temperature and battery condition. Take enough samples over enough days to make yourself statistically comfortable with the level of uncertainty you're targeting. Second, use the volumetric calibration procedure (as required for alternative test facilities) on both the SAC _and_ the OATS. Having done volumetric NSAs on high quality SACs and low quality OATS, I can say there is _no_ reason the OATS can be considered a gold standard in all instances. Lowell Kolb of Hewlett-Packard did an excellent paper on comparison of OATS sites a few years back. I would suggest looking up his paper for an idea of OATS site to site variation. Lastly, everything I've just said will, most likely, be totally swamped by variations in the EUT setup under real EUT testing unless you can _strictly_ control them. Don't go there. The more real the simulated EUT becomes, the more variables you introduce into the site evaluation. As more variables are introduced, the greater the number of data points will be required to resolve the result. While it is obvious to the most casual observer that the simple comb generator does not represent a real EUT, it does represent a single frequency component at a single phase component for each of the volumetric measurement points. The best work done in this area has used a VNA for evaluation of both quantities, but from the literature, this would appear to be most useful in diagnostic applications. Empirically, if the magnitude of the seven single planar volumetric points looks good, the site is _probably_ pretty good. Of course, if the SA is systematically off at all points, check the antenna calibration! Best regards, Brent DeWitt -Original Message- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of Rao, Praveen Sent: Sunday, January 06, 2002 6:16 PM To: emc-p...@majordomo.ieee.org Subject: Comparing EMI test results I'm trying to setup a programme to compare test results (for Radiated Emissions) between test labs. The plan is to circulate a Artifact around the labs and compare the results. The test sites being compared are Semi-anechoic Chambers v/s OATS. The source used is a wideband RF comb generator. I would like to understand the concept fully before I initiate this programme. Is there any information readily available on this topic? Any help will be greatly appreciated. Thanks. Praveen --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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. _ Send and receive Hotmail on your mobile device: http://mobile.msn.com
RE: Comparing EMI test results
Have the evaluation performed at both 3 meters and 10 meters. Should be interesting to see the results. John Shinn -Original Message- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of Rao, Praveen Sent: Sunday, January 06, 2002 7:14 PM To: Ken Javor; emc-p...@majordomo.ieee.org Subject: RE: Comparing EMI test results Thanks for the response. The purpose is to test both, the facility (semi-anechoic v/s OATS) and the quality of results. The comb generator is my first approach. A standard test sample(with cables) will follow. Any procedures, data, results, experience on this issue ? -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Monday, 7 January 2002 13:47 To: Rao, Praveen; emc-p...@majordomo.ieee.org Subject: Re: Comparing EMI test results Whether a comb generator is a good artifact depends somewhat on what your purpose is. If your purpose is to check how well calibrated the site is I think a comb generator is an excellent artifact because it is physically small and should generate the same radiation pattern at all facilities. But if your purpose is to check the quality of the testing done at different facilities including how good the test personnel are, then I believe you need a device with attached cables, since maximizing emissions will then involve not only height searches, but also rotation of the turntable and movement of the attached cables. Maybe you can attach a cable or two to the rf jack that normally seats the stub. on 1/6/02 8:16 PM, Rao, Praveen at praveen@fujitsu.com.au wrote: I'm trying to setup a programme to compare test results (for Radiated Emissions) between test labs. The plan is to circulate a Artifact around the labs and compare the results. The test sites being compared are Semi-anechoic Chambers v/s OATS. The source used is a wideband RF comb generator. I would like to understand the concept fully before I initiate this programme. Is there any information readily available on this topic? Any help will be greatly appreciated. Thanks. Praveen --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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.
Re: Comparing EMI test results
I read in !emc-pstc that Rao, Praveen praveen@fujitsu.com.au wrote (in e2eb942b4dd0db4c9ec86c89e592c958084...@mel0691.au.fjanz.com) about 'Comparing EMI test results', on Mon, 7 Jan 2002: I'm trying to setup a programme to compare test results (for Radiated Emissions) between test labs. The plan is to circulate a Artifact around the labs and compare the results. The test sites being compared are Semi-anechoic Chambers v/s OATS. The source used is a wideband RF comb generator. I would like to understand the concept fully before I initiate this programme. Is there any information readily available on this topic? Any help will be greatly appreciated. Thanks. Praveen Such tests are called 'round-robin tests', from an early form of subversive/samizdat communication - a letter bearing the signatures of several dissenters arranged in a circle so it was not possible to determine the order in which the signatures were added. A web search is likely to produce a lot of information. The main point that I remember about the protocol is that no results shall be disclosed by the testers until the circulation is complete, when all results are sent to the co-ordinators for consolidation. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk After swimming across the Hellespont, I felt like a Hero. --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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.
RE: Comparing EMI test results
Thanks for the response. The purpose is to test both, the facility (semi-anechoic v/s OATS) and the quality of results. The comb generator is my first approach. A standard test sample(with cables) will follow. Any procedures, data, results, experience on this issue ? -Original Message- From: Ken Javor [mailto:ken.ja...@emccompliance.com] Sent: Monday, 7 January 2002 13:47 To: Rao, Praveen; emc-p...@majordomo.ieee.org Subject: Re: Comparing EMI test results Whether a comb generator is a good artifact depends somewhat on what your purpose is. If your purpose is to check how well calibrated the site is I think a comb generator is an excellent artifact because it is physically small and should generate the same radiation pattern at all facilities. But if your purpose is to check the quality of the testing done at different facilities including how good the test personnel are, then I believe you need a device with attached cables, since maximizing emissions will then involve not only height searches, but also rotation of the turntable and movement of the attached cables. Maybe you can attach a cable or two to the rf jack that normally seats the stub. on 1/6/02 8:16 PM, Rao, Praveen at praveen@fujitsu.com.au wrote: I'm trying to setup a programme to compare test results (for Radiated Emissions) between test labs. The plan is to circulate a Artifact around the labs and compare the results. The test sites being compared are Semi-anechoic Chambers v/s OATS. The source used is a wideband RF comb generator. I would like to understand the concept fully before I initiate this programme. Is there any information readily available on this topic? Any help will be greatly appreciated. Thanks. Praveen --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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.
Re: Comparing EMI test results
Whether a comb generator is a good artifact depends somewhat on what your purpose is. If your purpose is to check how well calibrated the site is I think a comb generator is an excellent artifact because it is physically small and should generate the same radiation pattern at all facilities. But if your purpose is to check the quality of the testing done at different facilities including how good the test personnel are, then I believe you need a device with attached cables, since maximizing emissions will then involve not only height searches, but also rotation of the turntable and movement of the attached cables. Maybe you can attach a cable or two to the rf jack that normally seats the stub. on 1/6/02 8:16 PM, Rao, Praveen at praveen@fujitsu.com.au wrote: I'm trying to setup a programme to compare test results (for Radiated Emissions) between test labs. The plan is to circulate a Artifact around the labs and compare the results. The test sites being compared are Semi-anechoic Chambers v/s OATS. The source used is a wideband RF comb generator. I would like to understand the concept fully before I initiate this programme. Is there any information readily available on this topic? Any help will be greatly appreciated. Thanks. Praveen --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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.
