Yeah, it's a good lead into finding where the rpm related noise might be coming from. I was sure it was the alternator, but when it was sitting on the bench and I still had the noise, I went and bought a 6, no make that a 12 pack to forgot I ever got curious about chasing some little old EMI. And now I know the rest of the story... - Bill In the event of a national emergency, click on the following links to provide directions to your duly elected mis-representative.
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 ________________________________ From: Fred Townsend <[email protected]> To: Derek Walton <[email protected]> Cc: IEEE EMC Discussion Group <[email protected]> Sent: Mon, May 3, 2010 12:12:57 PM Subject: Re: Puzzle with noise source Derek, I agree with Ed's comments. I recall passing a Diesel Truck on the open highway. When I approached the rear of the semi trailer the squelch broke on my ham radio VHF transceiver. By the time I got along side the engine I could see the hood cover was missing. At the same time my receiver S-meter was pegged. With no ignition circuits what could be generating the terrific broad band noise. The fuel pump and super charger were on the top of my suspect list. Of course I never got to track down the source of the noise so I have wondered ever since. Fred Townsend Derek Walton wrote: > Good day folks, > > I have been investigating a radiated noise issue with an electrically driven Hydraulic pump. The INDUCTION motor is directly coupled to the pump which generates 10,000 psi at relatively low flow rates. The motor sits above the lid of a plastic tank: inside the tank sits the pump and the oil. > > NORMALLY, induction motors make little noise, so I was surprised to see emissions over the class A limit. In a nutshell I found: > > The noise looks like brush noise, but there are no brushes. It is not in sync with the power frequency, nor does it look like pole noise from the slots on the rotor. > > The motor when run seperately on the bench while initally noisey, becomes quiet as a mouse after bot 30 seconds, ever since it has been very quiet. A second motor exhibited this same performance. > > So, suspicions return to the hydraulic pump. Wrapping the plastic tank in AL foil ( even with nothing really to bond to ) knocks emissions down 10dB plus. The only thing in the tank is the pump and oil. So, is it possible for pumps to charge and discharge while moving the oil? The noise we see in real time on the SA is like rapid ESD events. To prove or eliminate this, is there a static disapative oil, or oil additive? > > Any other ideas of what could be the cause? > > We have eliminated the room as the source. > > Many thanks for suggestions, > > 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]> - 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]>
