Chris, The only other thing I can suggest doing is to trace the GPIB traffic to the instruments (particularly the signal generator) to determine the sequence of commands before and during the EUT failure. If you have a National Instruments GPIB interface, you can run the NI-Spy program and capture the GPIB traffic. You would use this information, along with the programming section of the sig-gen manual, to determine which commands are sent to the sig-gen. You should then be able to re-create the same sequence manually to determine if it is a specific squence that is causing the failure. However, this may not be conclusive since the timing of running it manually will not be the same as the automated sweep. We have an old copy of the Chase CIS9942 software, and it has a problem when stepping frequency. It will turn off modulation, step to the next frequency, check forward power, adjust sig-gen up/down if necessary, then turn modulation back on. It never drops the level until after it takes the forward power reading, and during that time it may overtest the product. Not usually a problem, since the level would have to drop more than 5dB for the peak of the modulation envelope to be less than the previous CW level, but it can happen. BTW, I have seen a couple of products fail a CW test but pass a modulation test, even when the peak modulation is 5dB higher than the CW level. Bob Richards, NCT
"Chileshe, Chris" <[email protected]> wrote: Group, On several occasions during radiated immunity EMC testing, I have observed products deviate or even fail and subsequent manual spot checks at the frequencies of interest have revealed no anomalous behaviour. I saw such behaviour on a product I was testing recently, and spent a long time conducting spot checks at the frequency and the immediate neighbourhood without much success replicating the failure. I tried turning the modulation on and off and even applying the modulated field instantly on and off without much success. I did a sweep again and the deviation was back like clockwork! What is the explanation for this and there are techniques for getting round this 'problem'? Rgds - Chris ---------------------------------------------------------------- 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/listserv/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: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
