Hi Grace, I'd like to take a little different stance to some of the other list member replies. Specifically I want to point out that the noise you see is NOT harmonics.
What is actually happening is that when the Triac turns on, there is a significant dV/dt that appears at the LISN terminal. While the wave produced is harmonic rich, the scanning receiver does not resolve spectral lines, it only draws a point on the graph each time the turn on occurs. When you are doing the formal sweep, you are scanning so slowly that it appears like you have a smooth(ish) line considerably above the noise floor. in reality, you are seeing pulses synchronized at the point in the line cycle. To show this happening what you need to so is speed the sweep rate very quickly, and observe th e effect of triggering the SA using the power line sync and ten free run. This shows exactly why you get the curve you do. I have charts somewhere here if you would like to see them, I cant attach them to this email. Of course, it follows the biggest spike follows the biggest transition which occurs at 90 and 270 degrees... Slowing the turn on time is the key to lowering the emissions, and that is more tricky than it sounds.... in practice. But usually, the noise dies on it's own by 5 or 6 MHz. I hope this helps. Sincerely, Derek Walton L F Research Grace Lin wrote: > Dear Members, > > Is there any specific instrument settings for taking power line > conducted emission? It seems the dimming function of a dimmer brings > up a lot of noise at low frequency such at 150 kHz. Disabling the > dimming function brings down the emission up to 30 dB at 150 kHz in > one case. > > Thank you. > > Best regards, > Grace Lin > - > ---------------------------------------------------------------- > 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] <mailto:[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] <mailto:[email protected]>> > Mike Cantwell <[email protected] <mailto:[email protected]>> > > For policy questions, send mail to: > Jim Bacher <[email protected] <mailto:[email protected]>> > David Heald <[email protected] <mailto:[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]>
