I can't offer quantitative experience, but I can offer some theory that has always made sense to me (and my results were usually quite repeatable at my last job where we employed these practices): While the measurement site itself probably has a defined ground plane for at least most of the ellipse, the surrounding earth also plays an important factor. For the best repeatability, an effective infinite ground plane is desirable. I remember we 'extended' our ground planes out and down into the ground around the sites. Due to our location over a town aquifer and the high water table (annoyingly high at times!), the effect was a good approximation of an infinite ground plane with very little fluctuation over time.
I could theorize that in Florida with sandy soil that would drain water/dry out more quickly, there would be more uncertainty due to the infinite ground plane property variations (does that phrase make sense?:). When it rained, the top surface would be a 'better' ground plane approximation and your site characteristics would change. When the top foot or so of sand dried out, it would cease to be a good infinite ground plane (- or at least change to a lossy one????) and your site characteristics would change again. Best Regards, Dave Heald -----Original Message----- From: richwo...@tycoint.com [mailto:richwo...@tycoint.com] Sent: Monday, July 08, 2002 8:11 AM To: emc-p...@ieee.org Subject: RE: Measurement Consistency of OATS We have noticed a change in our OATS characteristics depending upon the dampness of the area. It is especially noticeable this time of year when we get a lot of rain in Florida. Does anyone else experience this phenomena? More to your question Mat, the major contributors to the measurement uncertainty would be the repeatability of the setup of the EUT and test equipment (e.g., distance from EUT to antenna) and the stability/drift of the EUT and test equipment. Half of these parameters are human based (setup) and should vary less if the same person performs all of the tests. I have not seen a paper on this subject. Unually these variations are lighly covered in texts on measurement uncertainty. Richard Woods Sensormatic Electronics Tyco International -----Original Message----- From: Aschenberg, Mat [mailto:matt.aschenb...@echostar.com] Sent: Friday, July 05, 2002 10:49 AM To: emc-p...@ieee.org Subject: Measurement Consistency of OATS Hello, Have any of you seen a paper written on the measurement consistency of an OATS? If I were to have a product repeatedly measured at an OATS, how close should I expect the measurements to be? For sake of this example, there are no cables. All measurements are performed at the same OATS. The EUT is assumed not to change between tests. Mat ------------------------------------------- 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: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com 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: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list" ------------------------------------------- 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: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com 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: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list" ------------------------------------------- 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: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com 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: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
