John, Somewhere around here I have a plot of background noise in a 'new' electronic lab, the type with metal conduits.
The fields were 'specular' flat out to around 2kHz then rolled off and down until you could see the specular tones of the horizontal flyback from the old PC Monitors sitting around the lab and in the other rooms. The AC mains started in the range of 10nT although I've seen as high as 300nT, but whatever it starts at the harmonics roll down starting around 2kHz as though there's a single RC filter on the line. The tones at 15kHz coming from the old PC monitors are pretty energetic and there harmoniccs are constant out to around 3rd and 5th harmonics. The reason I mention specular, is because bandwidth won't change peak reading much. only broadband noise, like white noise is changed by the BW setting. I'll see if I can find the plot, it is VERY representative. uh, the A/m is of course, at 50/60Hz, B/uo = 10nT/(4 pi 1e-7) or about 78 dBuA/m assume the roll off at 2kHz, by 20kHz that should be 40 dB down, until the flyback F we're talking around 38 dBuA/m up to some maximum of 68 dBuA/m for our lab, which used knob and tubes in a wood building. I'll look for the plot Regards, Robert --- [email protected] wrote: From: John Woodgate <[email protected]> To: [email protected] Subject: [PSES] Magnetic noise level around 10 kHz Date: Fri, 6 Jul 2012 21:47:15 +0100 If you measured the background magnetic noise level in dBμA in a typical office at around 15 kHz, using an RBW of 300 Hz and a VBW of 1 kHz, what would be a typical result? Measurements at 3 kHz and every 3 kHz up to 24 kHz would be helpful but not essential. A result using a Schwartz beck FMB 1538 magnetic antenna would be particularly pertinent. I have an ill-informed agitator to combat. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk Instead of saying that the government is doing too little, too late or too much, too early, say they've got is exactly right, thus throwing them into total confusion. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - - ---------------------------------------------------------------- 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]>
