Hi Brian:
This additional information is crucial to understanding the issue and providing suggestions for resolving the issue. As I interpret your explanation, your equipment triggers on the input voltage waveform. If that waveform is distorted, the triggering will be in error. The triggering switches on the ac at various points on the waveform; the circuits then control the furnace temperature. I believe it is impossible to anticipate all the various supply voltage distortions. Non-linear loads create harmonic distortion. Rotating machines create transient overvoltage distortion. Large loads turning on or off create short-term low or high voltages. I suggest you consider internally generating a sinusoidal voltage that tracks the input voltage and use that for triggering the actual line voltage. Since heating is proportional to the rms value of the voltage, you might want to continuously measure the rms of the distorted line voltage, and use that value together with the regenerated sine wave to determine the trigger point. Best regards, Rich > -----Original Message----- > From: [email protected] [mailto:[email protected]] On Behalf > Of Kunde, Brian > Sent: Wednesday, November 08, 2006 8:43 AM > To: David Cuthbert; [email protected] > Subject: RE: Worst Case AC Power Conditions > > > Dave, > > Thanks for the reply. > > I should have explained further. Our equipment is designed to > work only in the 230V nominal voltage range at both 50 and 60 > hz. Our equipment has furnaces that we must regulate the > temperature within a very tight spec. To do this we must fire > control relays (SSRs) either at the zero crossing or use > phase control method. These methods require us to monitor the > AC line so to fire the SSR properly. As you can image, such > methods would be susceptible to AC line noise, harmonics, > dips, etc.. So we design immunity to such noise into our > products, but sometimes it is not enough. > > The other Brian > > - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
