Ken, I think that your expectations from an EMI point of view are quite realistic and present no greater hazard or problem in the light of the explosive atmosphere.
However, from the explosive atmosphere perspective, I would be very surprised if you could get a device like this certified as intrinsically safe. As you observe, the backlight is quite likely to use a higher voltage if electroluminescent, or require high current if LED. You need to remember that intrinsic safety limits voltage, current AND (not OR) energy under fault conditions. Most intrinsically safe circuits require protection at various points to limit current under fault conditions and also require careful attention to capacitances to avoid stored energy hazards. It is unlikely that a device that has not been designed with these specific requirements in mind will incorporate suitable circuitry. Creepage and clearance distances can also pose a problem, and I would expect to encounter that in a small hand-held device. You will also need to consider the batteries that are used, because you will often find that the clearances in many battery designs are less than those permitted by intrinsic safety standards. My company has experience with similar sized intrinsically safe equipment, so if you want to contact me off-line I may be able to help you further. Best regards Neil R. Barker CEng MIET FSEE MIEEE Manager Quality Engineering e2v technologies (uk) ltd 106 Waterhouse Lane Chelmsford Essex CM1 2QU UK Tel: (+44) 1245 453616 Fax: (+44) 1245 453571 Mob: (+44) 7801 723735 From: Ken Javor [mailto:[email protected]] Sent: 18 December 2006 15:37 To: [email protected] Subject: PDA back lighting potential Forum Members, I am evaluating a PDA-like device for EMI/explosive atmosphere usage. The device has what appears to be an LCD type display, which means it has back-lighting. While the device runs off 4.2 Vdc batteries, which are deemed a safe potential, I expect that the back-light potential is at a much higher level, and that getting from 4.2 Vdc to that higher potential can be potentially noisy from an EMI point-of-view. Any commentary/experience to share? Thank you, Ken Javor - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
