I didn't understand John's answer; I thought he said the prototype unit was too early, the production units too late, and the pre-production phase doesn't happen anymore.
In the military world, one or two of the first systems are designated for compliance testing (possibly testing them to death). As a prime contractor, you might have a few systems "shipped" into the field before all compliance tests are successfully completed, but you understand that the compliance testing might reveal some required modifications, and you are responsible to re-build those "shipped" units. Production turns on once the documentation of the compliance testing is accepted. Your Quality group is tasked with monitoring the uniformity of the production run and the uniformity of the parts and materials used, all the way down to requiring Certificates of Compliance for nit-picking things like the alloy of the solders used. If a vendor of a filter or SMPS changes their design and doesn't tell you, then your company has pretty good basis for complaining. Not only can you sue the vendor for all costs of an unauthorized change, you can also bring down government attention on the vendor (who likely has other military contracts at risk if he plays like that with you). If your contract extends for quite a while, or quite a number of units, it's probable that it is split up into incremental "buys", where field experience might suggest design changes. A compliance control board is tasked with determining if the changes warrant a new set of compliance tests. For instance, a different paint color might trigger a re-test for sun fading, but not for EMC or vibration. A new SMPS wouldn't affect humidity tests, but certainly would trigger transportation shock, vibration, EMC, thermal and power quality re-testing. Also, new MTBF's and MTTR's would be needed. In any case, over the length of a contract, your Quality guys are responsible for deciding if a new set of compliance tests are needed somewhere along the production run, simply to demonstrate the control of the Quality system. I recognize that in the commercial world, the cycle moves faster and you may have less control of your vendors. But that's not an excuse to happily accept that situation; I have the feeling that quality obsessed companies, say like Apple, have controls on their vendors that look very similar to the military system. Ed Price Chula Vista, CA USA -----Original Message----- From: McInturff, Gary [mailto:[email protected]] Sent: Wednesday, October 31, 2012 7:47 AM To: [email protected] Subject: Re: [PSES] Possible Counterfeit EMC Components? Morning Ed, John has it correct. A company that produces thousands or even hundreds of thousands generally scales up its builds and inventory of parts as the design matures, but nothing can go to production release unless the company is sure that the design meets its goals. You wouldn't want to have order 10,000 input line filters only to find out that the compliance test identified a problem with that part and it needed a change. The logistics of returning and purchasing the correct parts is quite expensive. Obviously the design team tries to verify as much as early as possible, but it can't (or certainly shouldn't) go full blown production until after Engineering design verification is complete. There should be no known issues on a design when its thrown over the wall to mass production - and manufacturing shouldn't accept it until they are convinced that the design is complete. As I read it - the designer did exactly what he should have done, his manufacturing arm doesn't! seem tied into his quality or design process or Design change request process and changed his design to reduce cost with no regard to performance. This happens a lot with off shore suppliers that aren't poorly monitored. I had a SMPS from a very large vendor that for the first two years we used the supply performed well. It had been used in several designs and had gone through a series of compliance tests successful. A new end product design which also used the power supply was going through final tests and the supply failed an immunity test. Since the supply had been used and verified in many other designs I assume a bad unit. After swapping it out a couple of more times it was obvious that something had changed. When I called the supplier to inquire I got "Oh you wanted one of those supplies". They had made some cost reductions without telling the customer base and they knew the supply no longer met the requirements but shipped it without changing the part number etc. T! here was no way that our purchasing department could tell anything was different. The vendor knew it but not his customers, and we certainly weren't the only customer of this "off the shelf" supply. The cost of purging inventory and the line shutdown while correct power supplies were shipped was very expensive for us. It might be noted that the vendor saved themselves lots of money, but they certainly didn't pass on the cost savings nor did they reimburse us for the cost of the inventory purge and lots production time. Some countries are almost famous for making cost reductions without verifying them. I think someone earlier pointed out that their supplier thought they could cut the cost of a motherboard if they took off all of those pesky "bypass" caps etc. As a military guy you likely familiar with MIL-TFP-41 (Make it like the F*&#$ print for once!) Sometimes you don't get what you pay for. To amplify Johns comments just a bit, one should do production audits but that can be prohibitively costly to do effectively when lots of product lines are involved. Gary -----Original Message----- From: John Woodgate [mailto:[email protected]] Sent: Wednesday, October 31, 2012 3:55 AM To: [email protected] Subject: Re: [PSES] Possible Counterfeit EMC Components? In message <[email protected]>, dated Wed, 31 Oct 2012, Ed Price <[email protected]> writes: >I thought that compliance testing was supposed to be done on the >"as-shipped" product, not the designer's prototype. Neither: the prototype is not representative and 'as shipped' is too late. Maybe the 'pre-production' phase has been eliminated from modern manufacturing, but it used to produce 5 to 10 sample products using the purchased parts and built under as close to production conditions as possible. In those days, some moulded parts might be replaced by fabricated parts, but with 3D printing.... These samples not only increase confidence in the design, and eliminate bugs, but can be used for compliance testing. -- OOO - Own Opinions Only. See www.jmwa.demon.co.uk The longer it takes to make a point, the more obtuse it proves to be. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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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://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]> - ---------------------------------------------------------------- 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://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]>
