We did some EMC testing last week (radiated emission in a chamber) on a ventilation system with two fans. It exceeded the limits on 145MHz.
Then outside the camber, we shut down the fans, we found the 145MHz on a bus line from a controller (3rd part product). Connecting the fans back again, the noise increase with increasing speed on the fans. Broadband noise at 145MHz. The troubleshooting process have been carried out outside the chamber (due to costs). We had a current clamp connected to a spectrum analyzer and measured every internal cable. 145MHz was only visible on the bus line and the cables to the fans (which are 2 meters long, unshielded). We inserted a CM choke on the bus line, and the 145MHz on the fan cable decreased by approximate 5 dB (current clamp meas.). What this would mean in decreased level under a radiated test, it’s hard to say. We are planning to check it out in the chamber next time. During that exercise, we will also prepare a better bonding of the fan cables to the chassis in order to reduse the radiated fields from the fan cables. Also have a shielded harness. Do you agree that the current clamp + spectrum analyzer, is a good tool for finding the noise and the wires that may act as antennas? Best regards Amund - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
