David is right about the BOM to some extent, but one useful technique to avoid a lot of time, trouble and expense every time you adjust just one component value is to calculate the limiting values for each component and produce a separate Intrinsic Safety BOM that has all components at their limiting values. For the most part this means a maximum value for each capacitor as the total stored energy in each circuit is the critical factor. This does mean that you have two separate BOMs to maintain, but the certified one won't change nearly as often. Make sure your design is well proven (don't skimp on the verification of all parameters) before you finalise the certification to avoid the extra expense and disruption of design changes early in the production life. Remember that you cannot implement a change in production until it has been agreed by the certification body. Best regards
Neil R. Barker CEng MIEE FSEE MIEEE Manager Compliance Engineering e2v technologies (uk) ltd 106 Waterhouse Lane Chelmsford Essex CM1 2QU UK Tel: (+44) 1245 453616 Fax: (+44) 1245 453410 Mob: (+44) 7801 723735 From: David Heald [mailto:[email protected]] Sent: 09 December 2005 04:50 To: Barker, Neil Cc: Chris Maxwell; [email protected] Subject: Re: Zone 1 Exia area (Explosion protection) Chris, How's it going? Niel obviously knows a lot more about the process than I do, but I can offer one practical bit of advice - I'm pretty sure you'll need a set-in-stone BOM when you get approval, so if you go for it have your components group check your suppliers to ensure there's no planned obsolescence of any parts in your device (or buy a LOT on the last-time-buy). It's a major undertaking, but it could be worth it if you enjoy a good challenge and your company can actually turn a profit from the devices :). BTW, FM is Factory Mutual. Happy Holidays all!! Best Regards, -Dave Heald On 12/8/05, Barker, Neil < [email protected]> wrote: Chris, What you are referring to is Hazardous Area equipment, or otherwise Electrical Equipment for use in Potentially Explosive Atmospheres. Exia refers to the classification of the protection; Ex for Explosive atmospheres, ia denotes intrinsic safety. You can readily find more information by searching the websites of UL or FM under Hazardous Area. For Australia, you would be best to seek an IECEx scheme certification. The relevant standards are in the IEC 60079 series. You could use one of the US based approvals bodies, such as UL, FM, SGS or Intertek, or you could seek certification in Australia with a body such as Simtars or TestSafe. Intrinsic safety does not involve a great deal of testing, but a considerable amount of assessment of equipment design. It is vitally important to have a good understanding of the principles of intrinsic safety before you start designing such equipment. The main aspect is that of limiting voltage, current or energy under fault conditions, with two countable faults in the case of ia certification. Circuits inevitably acquire additional components to provide the protection, typically extra resistors, clamp diodes, overvoltage protection devices, fuses and so on. Separation of circuits is also generally greater than would be required in normal environments. All of these factors serve to make your circuits occupy a bit more real estate than you may be used to. There are some useful reference books on the subject, such as "Intrinsically Safe Instrumentation: a guide" by Robin Garside; ISBN 0 9516848 1 7; published by Hexagon Technology Limited, Aylesbury, Buckinghamshire, UK. Best regards Neil R. Barker CEng MIEE FSEE MIEEE Manager Compliance Engineering e2v technologies (uk) ltd 106 Waterhouse Lane Chelmsford Essex CM1 2QU UK Tel: (+44) 1245 453616 Fax: (+44) 1245 453410 Mob: (+44) 7801 723735 From: Chris Maxwell [mailto: <mailto:[email protected]> [email protected]] Sent: 08 December 2005 14:21 To: [email protected] Subject: Zone 1 Exia area (Explosion protection) Happy holidays list dwellers. Thanks for a job well done and Best wishes to Rich Nute as well. He has now officially become a member of TLGTABATR (The Last Generation To Actually Be Able To Retire) Now who's going to keep me in line? Anyway we have a customer in Australia asking if we have a product that is rated for Zone 1 Exia (maybe a typo...could that be "Exit"). They have explained that this rating deals with mine atmospheres where there could possibly be mixtures of explosive gases. We have never tested products for such a condition. Can anybody tell me what standard this rating is based on? Furthermore, does anybody know who performs such testing and what it entails?\ Thanks, Chris Maxwell, Design Engineer | Compliance Engineer Email: <mailto:[email protected]> [email protected], Desk Phone: 315-266-5128 Engineering Department Fax: 315-797-8024 NetTest (New York) Inc. 6 Rhoads Drive, Building 4, Utica, NY USA Web: <http://www.nettest.com/> www.nettest.com, Phone: 315-797-4449 NetTest, a Member of the Anritsu Group - ---------------------------------------------------------------- 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
