That reminds me of a time when testing a desktop computer with a monitor sitting on top. It exhibited large amounts of EMI when the turn table was running and it stopped when the turn table stopped. And yes, it was not the turn table. It turns out that the weight of the monitor and the springingness (is that a word?) of the desktop cover bowed the cover down to almost touching a support bar. The vibration of the table moving was just enough to cause the cover being pressed down by the monitor towards the support bar to just bump into it. This intermittent contact made a large amount of EMI. Solutions - 2. Make sure the top cover and support bar always made good contact, or make sure it never made contact. Either worked. Assured contact worked better as it provided a shorter internal path to return EMI than the longer path across the perimeter of the cover to base.
My imagined clue in all this is the the vertical motor loads one end to the point of making an intermittent contact somewhere. - Bill In the event of a national emergency, click on the following links to provide directions to your duly elected mis-representatives. http://www.usa.gov/Contact/Elected.shtml or... https://writerep.house.gov/writerep/welcome.shtml http://www.senate.gov/general/contact_information/senators_cfm.cfm --- On Fri, 6/18/10, [email protected] <[email protected]> wrote: From: [email protected] <[email protected]> Subject: Hydraulic pump noise update To: [email protected] Date: Friday, June 18, 2010, 10:59 AM Good day all, A while back I wrote about an electrically powered hydraulic pump that had horrible radiated emissions. This is a brief update on what was found: First, all motors of the same type exhibited similar noise. Second, loading had some, but small effect on the noise. Temperature had little or no effect on the noise. The hydraulic pump was systematically inhibited until there were no moving parts: no effect. A second CE motor was used with similar results. In desperation the motor was bolted to the bench horizontally to begin looking into what could be happening and all noise ceased. It was rotated vertically and all noise returned. The motors, ALL motors including CE marked showed this effect. I don't have the paperwork on the motor, but I'm sure there was no EMC testing done since this was an induction motor. So, I'd like to make folks aware that INDUCTION motors are NOT necessarily noise free, and some evaluation should be made if you use them in anything other than horizontal. <http://o.aolcdn.com/cdn.webmail.aol.com/31844/images/common/space.gif> If anyone wants some of the graphs please let me know. If anyone has a cure for this, I'd be very interested. Sincerely, Derek Walton L F Research. - ---------------------------------------------------------------- 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.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. 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]> - 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.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. 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]>
