Amund, Open or connected screens? one theory states that the electric and magnetic field requirements are best served with opposing answers. However, we have found that when connecting a screen appears to cause a problem, it is worth persevering to track down the noise source and that keeping the screen connection is the best solution.
Where dissimilar connectors are used at the ends of a cable, there may not be a problem with leaving one screen connected. With identical connectors, BNC for example, then leaving one screen disconnected can be difficult to maintain. There is no guarantee that the installation engineers, maintenance engineers or customer will ensure the unconnected end is always positioned at the correct end. We had a similar problem a little while ago where a product that had been in production for some years was to be connected to a new design. In this instance, the screen was also used as the 0 volt dc return and connecting this to ground at the new product introduced all manner of ground loops. To overcome this, and enable a "standard" screened cable to be used, the BNC connector at the new interface was insulated from ground. Capacitors were then fitted at the inlet between the BNC "screen" and ground. This allowed the dc return to go unhindered to the power supply while shorting any rf induced onto the screen to ground. Testing the cable with BCI showed good rejection of interference at levels way above the specification. Regards, Neil Helsby ********************************************************************** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. This footnote also confirms that this email message has been swept by MIMEsweeper for the presence of computer viruses. www.mimesweeper.com ********************************************************************** ------------------------------------------- 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"
