EMC troubleshooting best done without EMC equipment

 Hi All,Now there is a provocative subject line, but to a large extent true in myexperience.Many engineers troubleshoot EMC problems using EMC measurements, such as inachamber, a conducted emission test setup, or ESD setup, after each proposedfix. This is a very slow way to proceed that does not yield as muchinformation possible about the mechanism. The chamber or other officialmeasurement should be used to confirm the fix one already has come up with.Ioften proceed at 10X or more the rate of narrowing down the problem thisway. It is very tempting to add fixes while still in the EMC lab but a lotofthe time this is not the way to proceed.I know some people who just spent a considerable amount of time over theholidays working on an EMC problem that could have been solved in a day,before the holidays, if they had stepped back from the EMC measurementitselfas a troubleshooting tool.I have found in my experience that about 90% of EMC failures should beinvestigated on the design bench and often using equipment that is notnormally used for EMC testing. Equipment and accessories like:* A good oscilloscope used in conjunction with a square plain wire loop(unshielded magnetic loop) and voltage probe together triggering on one orthe other and sometimes with the loop alone* A basic, low cost, spectrum analyzer used in conjunction with:   * A square plain wire loop (unshielded magnetic loop)   * Current probes   * Directional coupler and above loop or direct connection to measureresonant frequencies of physical structures * Good set of eyes! Anything movable in the equipment may lead touncertaintyin the emissions and should be tied down or otherwise renderedfixed. Effect to be measured by #1 and #2 above.* RF signal generator used in conjunction with a square loop and 3 WattClassA amplifier * A roll of "Slug and Snail" copper tape from the hardware store, sometimesused for shielding, grounding, or making half of a capacitor (problemcircuitis the other half). I don't think of the tape as a fix, but a"measurement" device, sometimes used with black electrical tape.* Pair of tweezers with insulated tips (bit of tape will do)* Random small pieces of cardboard * A collection of small value resistors of varying physical sizes, ~22 Ohms+/-50% * High voltage pulse generator with a big di/dt and coaxial output (not anESD simulator) Some of the above sounds like "MacGyver" stuff (remember the old televisionseries?), and it is!These are a few of the tools I use before going back to the EMC lab. Some ofthe items apply to emissions and others to immunity problems. Many of theabove make great live experiments for my courses.Doug-- University of Oxford Tutor Department for Continuing Education Oxford,Oxfordshire, United Kingdom
doug 5 years 8 months 24 days

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