Having built several 'environmental' chambers on the cheap and ad-hoc, I am (somewhat) qualified to comment on this. I have also converted a toaster oven for use as an at-home re-flow machine (yeah right, I have no life...).
Control signals to solid-state relays must be conditioned with care. Solid-state relays are leaky - I prefer a good relay or a contactor. Many toaster ovens will not survive long if used for thermal cycling, but are ok for use at a constant temperature setting. Toaster ovens are constructed to provide the user with thermal insulation, they are not designed to provide precise internal temperature control within the whole internal volume; so toaster ovens will probably require some form of internal circulation control. Toaster ovens are constructed to protect the user from shock by severely controlling user access. For use as an environmental chamber - control, power, and sensor lines to the UUT must cross this safety boundary. To submit data to agency, the toaster oven controller must conform to ISO17025 and be a calibrated device; so simple bang-bang controler will probably not succeed. I prefer a microprocessor-controlled PI or PID. A single temperature sensor will not suffice. The typical life of a converted toaster oven seems to be, at best, 250 hours. What is your time worth compared to buying a Blue-M oven off of ebay that will last for thousands of hours? If you must, the following can give you some ideas: www.circuitcellar.com/library/print/0704/Lacoste_168/index.htm ftp.circuitcellar.com/pub/Circuit_Cellar/2004/168/Lacoste_168.zip ftp.circuitcellar.com/pub/Circuit_Cellar/2007/199/Ihara-199.zip www.huv.com/blog/2007_03_01_archive.html Reliable software development tools are free or cheap for commonly available AVR and MSP430 microcontrollers, which I highly recommend for this sort of hack. luck, Brian > -----Original Message----- > From: [email protected] [mailto:[email protected]]On Behalf Of Robert > Johnson > Sent: Monday, January 07, 2008 1:14 PM > To: [email protected] > Subject: Precision Temperature Controlled Chamber > > http://www.designnews.com/contents/pdf/DN010708_GFBuildInstru > ctions.pdf > http://www.designnews.com/article/CA6515794.html?industryid=4 > 3664&nid=2337&rid=909500283 > <http://www.designnews.com/article/CA6515794.html?industryid= > 43664&nid=2337&rid=909500283> > > The next issue will be how to sell UL's Client Test Data > Program on your toaster oven. > > Bob Johnson - 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
