The heaters are good, but 40F is probably below the dewpoint, so if it is sealed well (RTV on the back the LED and power connector possibly?) put a decent sized desicant package and seal it up in a dry environment. Though a conformal coating couldnt hurt either. On Tue, Nov 18, 2008 at 4:34 PM, Carl Denk wrote: > I have a 18F1320 PIC with a temperature sensor and 2 pressure sensors > mounted in a waterproof gasketed aluminum box. There are sealed > penetrations for weatherproof connectors, except the power from a wall > wart with the usual concentric connector on the bottom face of the box, > and a LED and temperature sensor sticking through a tight fitting rubber > grommets.The sensors are potted in epoxy coated with 3 part urethane > paint. All this is mounted in an insulated enclosure with several backup > heaters that maintains temperature above 40F (4.4C) minimum. > > This is twice now, that the one pressure sensor (Motorola Freescale > MPX5700GP), after having the enclosure open for inspection for say 1/2 > hour in near freezing temperatures, that the pressure reading was what I > would think a maximum reading (110 PSI.). The sensor output is 0 - 5 > VDC, and appears to me that I'm getting a short from the 5VDC power > supply for the sensor to the signal pin. The first time, I replaced the > sensor immediately, but today, I waited a couple of hours, doing other > chores, and when I checked, pressure reading was normal (30 PSI.). The > board is thru the hole with solder mask double sided. After soldering, I > took special attention to clean the board of flux. The board has no > additional coating. > > I'm thinking it's condensation since the last time the aluminum box was > open, was much warmer temperatures and might have been light rain. What > would be appropriate actions- Coat most of the board with say a > catalyzed urethane clear paint (have stock of lots of it), let the > inside of the aluminum box open with cold low humidity ambient air (that > won't help if I open later in the summer though)? or?? > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- Jonathan Hallameyer -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist