Hello Derek - This sound like static induced in the system due to the liquid flow. Can you replace the oil with a different fluid and test again?
Best Regards Charles Grasso From: [email protected] [mailto:[email protected]] On Behalf Of Derek Walton Sent: Monday, May 03, 2010 8:04 AM To: IEEE EMC Discussion Group Subject: Puzzle with noise source 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]>
