It’s the holiday season again, when we celebrate the serious things in life and have some fun too.When EMC engineers come bearing gifts...tis NOT the season to be jolly. Fa-la-la, le-la-la-laa. In fact, it’s time to be worried. For to the EMC engineer, GIFTS is an acronym for: Grounding, Isolation, Filtering, Transient suppression, and Shielding. Sometimes it takes … [Read more...]
CM Feeling Bad, Check its Pulse
The last post examined CM radiation. Wow, what a problem! Over 100,000 microvolts/meter from a 3.5 ma signal. If the DM is normally the intended signal, where does the big common mode signal come from? Let’s take a look at that. The whole world seems to be enamored with high speeds. I know I could hardly wait to get a 1 GHz notebook. Did it help me … [Read more...]
And The CM Currents Go Round and Round
When we were discussing green electron current (differential mode) in the last post, I mentioned that common mode (CM) currents (red electrons) are typically caused by unbalanced differential mode (DM) currents. It’s pretty easy to visualize that in an unbalanced differential transmission system, one of the traces is longer, has an extra via, needs a branch, the spacing … [Read more...]
Mom! Dad! Do Open & Short Circuits Really Exist?
I debated whether I should introduce radiated pickup by the DM loop area next and then dismissed it so that I could continue with radiated emission from common mode (CM) currents. These tend to be very mysterious because they are typically caused by unbalanced differential mode (DM) currents. Often these are caused by a few extra grounds floating around somewhere in … [Read more...]
Upcoming Revision to the Medical Standard
We asserted last time that the existing amplifiers in the current test set up might be used to generate the higher stress levels if the test distance was reduced from 3 meters to 1 meter. As a reminder, we argued that testing at 1 meter means testing takes place in the near field as is the case for the threats faced by medical equipment (nearby cellphones etc.). Using the same … [Read more...]
Radiated Emission from Green Electron Current
Well . . . I’m back. I hadn’t planned on being out of print so long and it will take a few paragraphs to bring everyone up to date.A number of you learned at the IEEE EMC Symposium in Pittsburgh that my family and I were taking our little travel trailer on an extended camping trip immediately after the symposium. There were several National Parks that we have wanted … [Read more...]
Comment from Blog Reader Plus Test Field Calculations
Before launching into calculating the power required to create the test fields proposed by the upcoming medical standard, we have a comment from a blog reader on the realistic threats faced by electronic equipment….Comment from blog reader:I think the real question here is valid for all testing. Do we test according a repeatable verifiable and implementable and above all safe … [Read more...]
What is Differential and Common Mode Current?
Answering the title question will be a hot topic at the IEEE 2012 EMC Symposium in Pittsburgh. Hopefully many of you will have the chance to attend it this year. There are always some really great technical papers presented at this show – some more practical than others. If you’re there look me up. I’ll be spending some time at the Interference Technology booth, #817.The … [Read more...]
Unwanted Conductive and Radiative Emissions
The last post indicated that RF signal energy coupling from the emitter to the receptor can be by conduction or by radiation and that we would discuss that later. Well it’s later! The two coupling processes are very closely linked. Radiative coupling always starts out as a conductive signal and ends up as a conductive signal. In between and especially at … [Read more...]
The EMC Community Perspective
As indicated in a previous blog post, it seems hard to justify the rationale behind testing medical equipment for RF immunity at 3m distance. It is this greater test distance (as opposed to the 1m test distance accepted in automotive and MIL-STD testing) that is driving the high price of the replacement amplifiers. A change from the current test field strength of 10v/m @ 3m to … [Read more...]
