Perhaps “single-cycle RMS” would be better than “instantaneous” Ralph McDiarmid Product Compliance Engineering Solar Business Schneider Electric
From: dward [mailto:dw...@pctestlab.com] Sent: Friday, March 03, 2017 10:10 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] CORRECTION (wrong page) Passive Loop Emissions [General Use] Well, first, instantaneous does not mean zero, it means done in a short duration of time. So, there is no such thing as averaging in zero time. Dennis Ward This communication and its attachements contain information from PCTEST Engineering Laboratory, Inc., and is intended for the exclusive use of the recipient(s) named above. It may contain information that is confidential and/or legally privileged. Any unauthorized use that may compromise that confidentiality via distribution or disclosure is prohibited. Please notify the sender immediately if you receive this communication in error, and delete it from your computer system. Usage of PCTEST email addresses for non-business related activities is strictly prohibited. No warranty is made that the e-mail or attachments(s) are free from computer virus or other defect. Thank you. From: Bill Owsley [mailto:000000f5a03f18eb-dmarc-requ...@ieee.org] Sent: Friday, March 3, 2017 9:27 AM To: mailto:EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] CORRECTION (wrong page) Passive Loop Emissions [General Use] The "convention" for Instantaneous RMS is trending towards 0.707, the square root of 2 times the Peak. ________________________________________ From: John Woodgate <mailto:jmw1...@btinternet.com> To: mailto:EMC-PSTC@LISTSERV.IEEE.ORG Sent: Thursday, March 2, 2017 3:10 AM Subject: Re: [PSES] CORRECTION (wrong page) Passive Loop Emissions [General Use] RMS means 'root-mean-square' and 'mean' means 'average. For 'instantaneous', the averaging time is zero, so the RMS value is also zero. No trouble in meeting any limits, then. (;-) 'Instantaneous' should be changed to 'single-cycle', since that is technically correct. With best wishes DESIGN IT IN! OOO – Own Opinions Only http://www.jmwa.demon.co.uk/ J M Woodgate and Associates Rayleigh England Sylvae in aeternum manent. From: Bill Owsley [mailto:000000f5a03f18eb-dmarc-requ...@ieee.org] Sent: Thursday, March 2, 2017 5:04 AM To: mailto:EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] CORRECTION (wrong page) Passive Loop Emissions [General Use] "...since the 51.5 is derived from 20*log(377)" to be even more accurate, the 377 is the ratio of E/H, and for actual numbers (if I get this right) permittivity / permeability in a vacuum or free space or air since all are really close. We have recently acquired an E-field and H-field all in one probe in order to measure our near fields around an antenna for exposure requirements at low frequencies. We have to figure out Instantaneous RMS units in this world. Another convention ! We also have to check our radiated emissions, usually harmonics of the fundamental, to the limits. Since generically, the source impedance is not known in the near field, and it is also changing very rapidly over short distances, certain assumptions, conventions, are made in order to be consistent in the industry. The approximate 51.5 db conversion is not accurate, but if everyone does it, and the standards do as well, the results are the same. ps. and the H-field does roll off by the 3rd order just as the physics seem to imply. The measurement uncertainty is rather large in this area, since the data seems to have a wide range of values, but given enough points over a wide range of measurements, and averaging, the roll off converges on the 3rd order, in the near field. And the environment has a noticeable effect on the results. Intuitive when thought about. For low frequencies, the environment is integral to the antenna. Dirt, wet or dry and in between, metal ground plane or something else, like dirt, or concrete, or something else. Way different environmental conductivities affecting the results. I suspect that early low frequency wireless transmissions science did not entirely carry forward for the rest of us to learn and understand. The early digital transmissions were wired and gave us the telegraphers equations, which are still valid. But the rest seem to have faded into the past. ________________________________________ From: "Sundstrom, Mike" <mailto:mike.sundst...@garmin.com> To: mailto:EMC-PSTC@LISTSERV.IEEE.ORG Sent: Tuesday, February 28, 2017 8:46 AM Subject: Re: [PSES] CORRECTION (wrong page) Passive Loop Emissions [General Use] Not much different from any other in situ testing I've ever done. Guess I looked like a mad scientist and didn't know it. Thanks, Michael Sundstrom Garmin Compliance Engineer 2-2606 (913) 440-1540 KB5UKT "We call it theory when we know much about something but nothing works, and practice when everything works but nobody knows why." -- Albert Einstein -----Original Message----- From: Cortland Richmond [mailto:mailto:k...@earthlink.net] Sent: Monday, February 27, 2017 8:14 PM To: mailto:EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] CORRECTION (wrong page) Passive Loop Emissions [General Use] On 2/27/2017 7:53 PM, Brent DeWitt wrote: > I think Ken's rational makes sense to me, since the 51.5 is derived from > 20*log(377). > > Sure, but now we're back to how close we are -- wavelengths -- to the emitter. 20*log(??) Low frequencies can be tricky, and I once had to double-check a test lab (not yours) results at a vendor, dragging the EUT out to their parking lot then wheeling a cart with a 6510 loop antenna, battery, AOR AR5000 receiver and RMS voltmeter [all mine] away to see how fast the signal dropped with distance compared to 3m. A fun time was NOT had, but I probably came across as a mad scientist. Again. At least no one ran out of a chamber... Cortland Richmond KA5S - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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