Hi guys, Being that EMC is a side job for me. I have not been able to build an official ESD target.
We calibrate our EMC test equipment (which includes an ESD gun and a multifunction transient generator EFT, Surge...) on a yearly basis. Between calibrations, I have some relatively simple methods that I use to check the equipment. For the ESD generator, I put on the air discharge tip, charge it up to 8KV and SLOWLY approach it to the ground reference plane of our setup. When the tip gets close enough to the plane, the spark jumps. After doing this many times, I've developed a "feel" for how far away the gun should be before the spark jumps and a "feel" for how the snap sounds. I know that there is all sorts of room for error here. I also feel that there is all sorts of room for error in any home-grown verification setups. Of course, if you actually go through the trouble of building the official "target", use a 1GHz waveform capture scope in a Faraday cage... then you would have a verification method that is far more accurate than mine. But mine costs nothing. So my benefits/cost ratio is tough to compete with. My feeling is that the test method for ESD has more bearing on the results than equipment differences. This is where I spend my time and effort. For the EFT generator, I turn on a radio in the room. When the EFT generator is operating, the interference from the generator makes audible clicks in the music from the radio (it works for AM and FM). This saved my butt big time once. Our EFT generator had a relay failure and wasn't putting out any signal at all. There was no indication of this from the unit. However, I didn't hear interference from the radio. I immediately swapped out the DUT with an old unit that fails EFT miserably....no failure. I sent the unit back... sure enough, it was broken. If I didn't have the radio on, I would have tested eight more months worth of "passing" tests before I sent the unit back for cal and found out that it was broken. Again, a huge benefits/cost ratio. I have since refined this method. I now use our spectrum analyzer. It is in the same room as the EFT generator. I hook a homemade nearfield probe (a 1m length of coax with it's end cut and center conductor protruding) to the spectrum analyzer input. I then set the analyzer to a 100MHz span with a 50Mhz center frequency. When I use the EFT generator, I turn on this spectrum analyzer setup and observe the screen. The EFT generator interference from across the room produces a spectrum on the display that I am now familiar with. If I don't see this spectrum, then I know that something is up. This is still essentially free since I have the spectrum generator and near field probe anyway. One thing that I haven't figured out yet is how to easily verify the surge operation of the transient generator. (other than the brute force method below) My ultimate fallback confidence check is one of our good old LP-5000 series instruments. They were designed before the EMC directive came to be. So, they fail ESD, EFT, Surge... miserably. When in doubt, I hook one of them up. If it fails, then I at least have some confidence in my test equipment. Hey mon, got to get to work. Chris Maxwell | Design Engineer - Optical Division email [email protected] | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [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://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
