Brian: In general I agree with you. Let's not over test more than we have to. Although it may be hard to quantify what is excessive. I think part of the rationale for doing humidity/temperature exposures at higher than practical conditions is based on the product being built. Example: Your product has sensitive circuitry that can be influenced by moisture/high humidity condition resulting in leakage paths or signal alteration. Then instead of testing at 35C/75% you might want to use a slightly higher condition such as 35C/85% to prove out the design. Then use a similar approach to monitor material and processing conditions to provide an acceptable product. Set the bar a little higher than needed i.e. at 11/10ths to assure day in and day out product quality. Let me give you an example (similar to yours below) of where higher than ambient achievable testing conditions may be needed. If you are manufacturing HVAC test and measurement equipment you could be going from a -20C refrigerated environment to an outside 35C+ high humidity condition such as the Florida Keys. This can cause moisture conditions to form in the meter which can effect the measurement circuitry resulting in an inaccurate reading. In this case you should be testing at higher than the 35C/75% real world condition. Regards Michael Barmuta Staff Engineer Fluke Corp. Everett WA 425-446-6076 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis Sent: Thursday, June 01, 2006 7:02 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 ----------------------------------------------------- This message (including any attachments) contains confidential and/or proprietary information intended only for the addressee. Any unauthorized disclosure, copying, distribution or reliance on the contents of this information is strictly prohibited and may constitute a violation of law. If you are not the intended recipient, please notify the sender immediately by responding to this e-mail, and delete the message from your system. If you have any questions about this e-mail please notify the sender immediately. --------------------------------------------------- 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 -----------------------------------------------------