Hi all, We have personally experienced an interesting phenomenon. We build a certain circuit that detects a 20Khz tone. This circuit is housed in a product that has an EMI spray coated case. One of our engineers noticed that our techs on the manufacturing floor were having a difficult time setting up units on the floor. The tone detect circuit kept getting set off for apparantly no reason.
However, back in the engineering lab, we have no problems. So we did a little experiment. We took a unit out to the manufacturing floor and opened its case (which is how they work on them in manufacturing). We held it up near the lights. The tone detect circuit went crazy. We put the unit down on the bench. No problem. But, if you leave it opened up on the bench and hold your hand over the board, the circuit goes off again. When we close up the case work, all of these problems go away. So, our obvious solution is to make a modified casework with "tweaker holes" so that manufacturing personnel can tweak the amplifier pots with the casework closed. But.... I'm still curious. What's causing the interference? I was wondering if flourescent light ballasts could be giving off an emission in the KHz range. (Maybe that's why holding it to the lights sets it off.) But what about the hand waving? If I assume the ballasts are giving off emissions, can I also assume that the human body can change the local field pattern? Am I barking up the wrong tree? Maybe its the LAN cables in the ceiling? Anybody else have a similar experience or some insight into this? Thanks, Chris Maxwell | Design Engineer - Optical Division email chris.maxw...@nettest.com | 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
