Cynthia Pleach wrote: > I don't know about all of you, but I am sick of arguing with > hardware engineering managers about what constitutes > a passing EMC test and what does not.
Hear! Hear! > I have seen companies impose a 6dB margin requirement, > some 5 dB, and some 3dB. > > I have made the recommendation that the minimum here > should be 3dB. I thought that this was fair. Now comes > the product that has 2.8dB margin. Being a stick by the > rules type of person, I listened to the engineer explain > that it was the lousy PC his card was in not his card. So > I suggested that we prove his theory, purchase a new > machine and check the old machine versus the new > one and if there is an improvement, that I would let > the 2.8dB stand. > > Of course the manager of the group tells me that as > a recommendation 3dB is good, but as a rule it > is IRRESPONSIBLE. Thus I end up with the "be > a b___ch" option of imposing the retest for the .2dB > or starting a precedence of well if .2 is okay, is .3 etc. > etc. > > What I would like to do is take a pole. (must be election > year in the USA!!!!!!!!!!!) I would like all of you to respond > as to what you feel is appropriate. Then I'll run the > stats and let you what the results are. This way I can > go back to the manager with the number of certification > experts that responded and what they thought was right. > > He or I will have a hard time arguing against stats. > (I am open to the possibility that I am wrong and > 0 margin is acceptable). > > Just reply with a number and I'll let you know what happens. > > Thanks > Cynthia > > [email protected] Cynthia, 6dB would be comfortable. Unfortunately, I have been in a lab that passed at only 0.5dB. To throw another angle on the subject, try this on for size. The 80/80 rule (80% of the products pass 80% of the time) falls under the vail of a Binomial Distribution: 1. Two outcomes during the trials: pass or fail. 2. Probability of success is constant throughout the trials. 3. Number of trials is constant. 4. Each trial is independent. Try running a binomial distribution calculation on N = 100 things, where x = 80 things succeed with a p = 0.8 succes rate. Cumulative answer here. In other words, calculate "at most". I think you'll be very surprised at the outcome. ******************************************************* Doug McKean [email protected] ------------------------------------------------------- The comments and opinions stated herein are mine alone, and do not reflect those of my employer. ------------------------------------------------------- *******************************************************
