EMC performance is not always just about meeting standards, it’s also (well, sometimes anyway) about producing a reliable, quality product. The former does not necessarily lead to the latter, and you often have to go beyond the requirements of the standards to achieve real-world immunity. I’ve been using the chattering relay, the DC motor, and other ‘real world’ interfering sources since the early 80's. Other EMI sources I use are switching banks of incandescent lamps on and off (high inrush surge), walkie-talkie or CB radio keying (common high field strength RF sources), switching AC motors on/off (inductive kick on switch-off), and piezo spark igniter from a domestic cooking hob operated in the proximity of the EUT (fast EM impulse). It often takes protection measures above and beyond those required just to meet the standardsto make products immune to these real-world interferring sources. Just as an aside, a DC motor will often produce different EMI profiles according to the direction (+/- vs. -/+) it is run. This caused me considerable consternation during radiated emissions testing when the EUT would easily pass with a motor running in one direction and fail with it running in the reverse direction. Investigation showed it was due to the brushes bouncing more in one direction than the other, see below. Considering a typical low cost DC motor, the ‘(O)’ represents the contacts on the rotating shaft, the ‘u’ & ‘n’ the brushes and the ‘- - -‘ the springy contacts which keep the brushes pressed to the shaft and come out of the motor as terminals 'x'. As shown below, the brushes will ‘bounce’ more with the shaft rotating CCW than when rotating CW. x---u (O) n---x ----- Original Message ----- From: Ken Wyatt Sent: 02/22/13 06:45 PM To: [email protected] Subject: [PSES] Try these unusual EMI sources to check immunity
Hi All, Try these unusual EMI sources to check the radiated or conducted immunity of your circuit or product! http://www.tmworld.com/electronics-blogs/the-emc-blog/4407544/Unusual-EMI-Sources Just posted on the Test & Measurement World "EMC Blog". Cheers, Ken ___________________ Kenneth Wyatt Wyatt Technical Services LLC Woodland Park, CO [email protected] Web http://www.emc-seminars.com Newsletter http://emc-seminars.us1.list-manage.com/subscribe?u=987f203d1f64dd89f06b0c3f5&id=a00f29a904 Connect with me on LinkedIn http://www.linkedin.com/in/kennethwyatt ! - ---------------------------------------------------------------- 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] > - ---------------------------------------------------------------- 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]>
