Very well placed point Brian! A thing that makes a difference between the heavy industry and civil engineering, on one hand, and the electronics industry on the other is that in the heavy world you can compute almost everything. Based on stress, strain and safety coefficients, man has developped formulae that can be used to optimize constructions and you can get minimum material consumption at minimum labor costs. This is why we can build bridges, sky scrapers and roller coasters and know they will not collapse. This is not exactly true for the electronics world. With the exception of reliability, there doesn't seem to be much calculus involved. We cannot even compute if a panel will warp in the oven or not. Why? Maybe because the industry is still young and there is not enough empirical data for developping efficient models. So my bet is that you are right, we definately exaggerate, to buffer up for the unknown. Ioan -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Brian Ellis Sent: Thursday, June 01, 2006 10:02 AM To: [log in to unmask] Subject: [TN] Do we exaggerate? I have discovered that there is a real limit to the conditions of natural temperature and humidity that are possible. To put it simply, if the temperature and humidity are high at ground level, clouds will form at a given altitude, reflecting solar radiation. This will result in a lowering of the temperature. I haven't yet determined the exact limit conditions, but it would seem that (very roughly), you can obtain 100% RH only if the temperature is under about 15°C. At 25°C, the max humidity is ~85%. At 35°C, 75%. At 50°C, 55%. When I have more exact data, it is clear I'll be able to determine a limit curve, on the right side of which it will be impossible for natural conditions to exist. However, we can create conditions in climatic chambers which will be far to the right of the curve, and we use such conditions in SIR/ECMR testing. Are we exaggerating when we pump up the temperature and humidity to excessive levels, to create conditions which can never occur in real life? Is there even a rationale to do so? Remember that the inside of an enclosure with active electronics is warmer than ambient. The real dangerous conditions are with high humidities, which can occur only at artificially low temperatures, such as when going into a tropical rain forest conditions from an over-air-conditioned room (e.g., 20°C to 30°C/80% RH), when condensation may occur for a short time. Views are welcome, please. Brian -- http://www.cypenv.org Cyprus environment/energy http://www.cypenv.org/worldenv World environment/energy http://www.cypenv.org/weather Cyprus weather http://www.cypenv.org/smf/index.php Environment/energy forums http://groups.yahoo.com/group/cypnature/ Cyprus nature forum --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------