Let me add a bit to Doug Nix's comments. For the United States, the applicable standard is UL 1998. http://ulstandardsinfonet.ul.com/scopes/scopes.asp?fn=1998.html I strongly recommend implementing interlocks in hardware. The UL group that handles software and firmware testing is backlogged and works slowly. There will also be limits on what you can do to update electronics and firmware. The amount of testing required is very extensive because there are may types of single faults that could occur that may result in a hazards.
Search for "Therac 25" at Google or some other search engine and you will see one of the worst-case results of a reliance on silicon for interlocks. Ted Eckert American Power Conversion/MGE http://www.apc.com/ The items contained in this e-mail reflect the personal opinions of the writer and are only provided for the assistance of the reader. The writer is not speaking in an official capacity for APC-MGE or Schneider Electric. The speaker does not represent APC-MGE's or Schneider Electric's official position on any matter. "Kunde, Brian" <brian_kunde@leco tc.com> To Sent by: <[email protected]> [email protected] cc Subject 07/20/2007 08:29 Interlock Circuits Firmware/Silicon AM Controlled I have limited experience working with industrial machines with moving parts so I would appreciate any help you can provide. To protect an operator from moving parts, my understanding is that I have to use an approved interlock device (in this case a switch) and it has to directly control the device that makes the motion (pneumatic solenoid). But on a future project, we would like to have the interlock switch talk to an FPGA (silicon) and have firmware and software controls the motion device after many sensor checks are made. These "checks" are quite complex where many things have to be just right in the right sequence for the motion to occur. Engineering is saying that the sequence is too complex to limit with a simple interlock switch system. Is it possible to use silicon chips, firmware, and software in such a circuit? Can such an approach be used and if so what is involved in qualifying it? Thanks, The Other Brian LECO Corporation Notice: This communication may contain confidential information intended for the named recipient(s) only. If you received this by mistake, please destroy it and notify us of the error. Thank you. - 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 ______________________________________________________________________
